Validate expression block-scalar chomping

2025-11-22 05:43:40 +00:00
12 changed files with 2923 additions and 10 deletions
@@ -0,0 +1,58 @@
+import {registerLogger} from "./log";
+import {createDocument} from "./test-utils/document";
+import {TestLogger} from "./test-utils/logger";
+import {clearCache} from "./utils/workflow-cache";
+import {validate} from "./validate";
+
+registerLogger(new TestLogger());
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("block scalar chomping - allowed cases", () => {
+  it("does NOT warn for step.run with clip chomping (exception)", async () => {
+    const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: |
+          echo \${{ github.event_name }}
+`;
+    const result = await validate(createDocument("wf.yaml", input));
+
+    expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+  });
+
+  it("does not warn for inline expression", async () => {
+    const input = `
+on: push
+jobs:
+  build:
+    if: \${{ github.event_name == 'push' }}
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+    const result = await validate(createDocument("wf.yaml", input));
+
+    expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+  });
+
+  it("does not warn for quoted string", async () => {
+    const input = `
+on: push
+jobs:
+  build:
+    if: "\${{ github.event_name == 'push' }}"
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+    const result = await validate(createDocument("wf.yaml", input));
+
+    expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+  });
+});
@@ -0,0 +1,142 @@
+import {DiagnosticSeverity} from "vscode-languageserver-types";
+import {registerLogger} from "./log";
+import {createDocument} from "./test-utils/document";
+import {TestLogger} from "./test-utils/logger";
+import {clearCache} from "./utils/workflow-cache";
+import {validate} from "./validate";
+
+registerLogger(new TestLogger());
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("block scalar chomping - boolean fields", () => {
+  describe("job continue-on-error", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    continue-on-error: |
+      \${{ matrix.experimental }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    continue-on-error: |+
+      \${{ matrix.experimental }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    continue-on-error: |-
+      \${{ matrix.experimental }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("step continue-on-error", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        continue-on-error: |
+          \${{ matrix.experimental }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        continue-on-error: |+
+          \${{ matrix.experimental }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        continue-on-error: |-
+          \${{ matrix.experimental }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+});
@@ -0,0 +1,188 @@
+import {DiagnosticSeverity} from "vscode-languageserver-types";
+import {registerLogger} from "./log";
+import {createDocument} from "./test-utils/document";
+import {TestLogger} from "./test-utils/logger";
+import {clearCache} from "./utils/workflow-cache";
+import {validate} from "./validate";
+
+registerLogger(new TestLogger());
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("block scalar chomping - if fields", () => {
+  describe("job-if", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    if: |
+      \${{ github.event_name == 'push' }}
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    if: |+
+      \${{ github.event_name == 'push' }}
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    if: |-
+      \${{ github.event_name == 'push' }}
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+
+    it("errors without ${{ }} (isExpression)", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    if: |
+      github.event_name == 'push'
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("uses > indicator in error message for folded scalars", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    if: >
+      \${{ github.event_name == 'push' }}
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '>-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+  });
+
+  describe("step-if", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: |
+          \${{ github.event_name == 'push' }}
+        run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: |+
+          \${{ github.event_name == 'push' }}
+        run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks boolean evaluation. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - if: |-
+          \${{ github.event_name == 'push' }}
+        run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+});
@@ -0,0 +1,428 @@
+import {DiagnosticSeverity} from "vscode-languageserver-types";
+import {registerLogger} from "./log";
+import {createDocument} from "./test-utils/document";
+import {TestLogger} from "./test-utils/logger";
+import {clearCache} from "./utils/workflow-cache";
+import {validate} from "./validate";
+
+registerLogger(new TestLogger());
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("block scalar chomping - number fields", () => {
+  describe("job timeout-minutes", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: |
+      \${{ matrix.timeout }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: |+
+      \${{ matrix.timeout }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: |-
+      \${{ matrix.timeout }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("container.ports", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      ports: |
+        \${{ fromJSON('[80, 443]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      ports: |+
+        \${{ fromJSON('[8080, 9090]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      ports: |-
+        \${{ fromJSON('[80, 443]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("container.volumes", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      volumes: |
+        \${{ fromJSON('["/data:/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      volumes: |+
+        \${{ fromJSON('["/data:/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: node:16
+      volumes: |-
+        \${{ fromJSON('["/data:/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("services.ports", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        ports: |
+          \${{ fromJSON('[5432]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        ports: |+
+          \${{ fromJSON('[5432]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        ports: |-
+          \${{ fromJSON('[5432]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("services.volumes", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        volumes: |
+          \${{ fromJSON('["/var/lib/postgresql/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        volumes: |+
+          \${{ fromJSON('["/var/lib/postgresql/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:14
+        volumes: |-
+          \${{ fromJSON('["/var/lib/postgresql/data"]') }}
+    steps:
+      - run: echo hi
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+
+  describe("step timeout-minutes", () => {
+    it("errors with clip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        timeout-minutes: |
+          \${{ matrix.timeout }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("errors with keep chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        timeout-minutes: |+
+          \${{ matrix.timeout }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result).toContainEqual(
+        expect.objectContaining({
+          message:
+            "Block scalar adds trailing newline which breaks number parsing. Use '|-' to strip trailing newlines.",
+          code: "expression-block-scalar-chomping",
+          severity: DiagnosticSeverity.Error
+        })
+      );
+    });
+
+    it("does not error with strip chomping", async () => {
+      const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo hi
+        timeout-minutes: |-
+          \${{ matrix.timeout }}
+`;
+      const result = await validate(createDocument("wf.yaml", input));
+
+      expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+    });
+  });
+});
@@ -0,0 +1,227 @@
+import {DiagnosticSeverity} from "vscode-languageserver-types";
+import {registerLogger} from "./log";
+import {createDocument} from "./test-utils/document";
+import {TestLogger} from "./test-utils/logger";
+import {clearCache} from "./utils/workflow-cache";
+import {validate} from "./validate";
+
+registerLogger(new TestLogger());
+
+beforeEach(() => {
+  clearCache();
+});
+
+describe("expression validation", () => {
+  describe("block scalar chomping - fields that warn only for clip", () => {
+    describe("env", () => {
+      it("warns with clip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: |
+          echo $VAR
+        env:
+          VAR: |
+            \${{ matrix.value }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result).toContainEqual(
+          expect.objectContaining({
+            message:
+              "Block scalar adds trailing newline to expression result. Use '|-' to strip or '|+' to keep trailing newlines.",
+            code: "expression-block-scalar-chomping",
+            severity: DiagnosticSeverity.Warning
+          })
+        );
+      });
+
+      it("does not warn with keep chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: |
+          echo $VAR
+        env:
+          VAR: |+
+            \${{ matrix.value }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+
+      it("does not warn with strip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: |
+          echo $VAR
+        env:
+          VAR: |-
+            \${{ matrix.value }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+
+      it("uses > indicator in warning message for folded scalars", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: |
+          echo $VAR
+        env:
+          VAR: >
+            \${{ matrix.value }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result).toContainEqual(
+          expect.objectContaining({
+            message:
+              "Block scalar adds trailing newline to expression result. Use '>-' to strip or '>+' to keep trailing newlines.",
+            code: "expression-block-scalar-chomping",
+            severity: DiagnosticSeverity.Warning
+          })
+        );
+      });
+    });
+
+    describe("action input", () => {
+      it("warns with clip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: |
+            \${{ github.ref }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result).toContainEqual(
+          expect.objectContaining({
+            message:
+              "Block scalar adds trailing newline to expression result. Use '|-' to strip or '|+' to keep trailing newlines.",
+            code: "expression-block-scalar-chomping",
+            severity: DiagnosticSeverity.Warning
+          })
+        );
+      });
+
+      it("does not warn with keep chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: |+
+            \${{ github.ref }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+
+      it("does not warn with strip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: |-
+            \${{ github.ref }}
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+    });
+
+    describe("matrix value", () => {
+      it("warns with clip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: |
+          \${{ fromJSON('[1, 2, 3]') }}
+    steps:
+      - run: echo hi
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result).toContainEqual(
+          expect.objectContaining({
+            message:
+              "Block scalar adds trailing newline to expression result. Use '|-' to strip or '|+' to keep trailing newlines.",
+            code: "expression-block-scalar-chomping",
+            severity: DiagnosticSeverity.Warning
+          })
+        );
+      });
+
+      it("does not warn with keep chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: |+
+          \${{ fromJSON('[1, 2, 3]') }}
+    steps:
+      - run: echo hi
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+
+      it("does not warn with strip chomping", async () => {
+        const input = `
+on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: |-
+          \${{ fromJSON('[1, 2, 3]') }}
+    steps:
+      - run: echo hi
+`;
+        const result = await validate(createDocument("wf.yaml", input));
+
+        expect(result.filter(d => d.code === "expression-block-scalar-chomping")).toEqual([]);
+      });
+    });
+  });
+});
@@ -3,12 +3,14 @@ import {Expr} from "@actions/expressions/ast";
 import {ParseWorkflowResult, WorkflowTemplate, isBasicExpression, isString} from "@actions/workflow-parser";
 import {ErrorPolicy} from "@actions/workflow-parser/model/convert";
 import {splitAllowedContext} from "@actions/workflow-parser/templates/allowed-context";
+import {Definition} from "@actions/workflow-parser/templates/schema/definition";
 import {BasicExpressionToken} from "@actions/workflow-parser/templates/tokens/basic-expression-token";
 import {StringToken} from "@actions/workflow-parser/templates/tokens/string-token";
 import {TemplateToken} from "@actions/workflow-parser/templates/tokens/template-token";
 import {TokenRange} from "@actions/workflow-parser/templates/tokens/token-range";
 import {File} from "@actions/workflow-parser/workflows/file";
 import {FileProvider} from "@actions/workflow-parser/workflows/file-provider";
+import {Scalar} from "yaml";
 import {TextDocument} from "vscode-languageserver-textdocument";
 import {Diagnostic, DiagnosticSeverity, URI} from "vscode-languageserver-types";
 import {ActionMetadata, ActionReference} from "./action";
@@ -106,6 +108,8 @@ async function additionalValidations(
        config?.contextProviderConfig,
        getProviderContext(documentUri, template, root, token.range)
      );
+
+      validateChomp(diagnostics, token, parent, key, validationDefinition);
    }

    if (token.definition?.key === "regular-step" && token.range) {
@@ -217,3 +221,98 @@ async function validateExpression(
    );
  }
 }
+
+function validateChomp(
+  diagnostics: Diagnostic[],
+  token: BasicExpressionToken,
+  parent: TemplateToken | undefined,
+  key: TemplateToken | undefined,
+  validationDefinition: Definition | undefined
+): void {
+  // Not "clip" or "keep" chomp style?
+  if (token.chompStyle !== "clip" && token.chompStyle !== "keep") {
+    return;
+  }
+
+  // No definition? This can happen when the token is in an invalid position or the workflow has parse errors.
+  if (!validationDefinition) {
+    return;
+  }
+
+  // Step "run"?
+  if (parent?.definition?.key === "run-step" && key?.isScalar && key.toString() === "run") {
+    return;
+  }
+
+  // Block scalar indicator, i.e. | or >
+  const scalarIndicator = token.scalarType === Scalar.BLOCK_LITERAL ? "|" : ">";
+
+  const defKey = validationDefinition.key;
+  const parentDefKey = parent?.definition?.key;
+
+  // Error for boolean fields
+  if (
+    defKey === "job-if" ||
+    defKey === "step-if" ||
+    defKey === "step-continue-on-error" ||
+    (parentDefKey === "job-factory" && key?.isScalar && key.toString() === "continue-on-error")
+  ) {
+    diagnostics.push({
+      message: `Block scalar adds trailing newline which breaks boolean evaluation. Use '${scalarIndicator}-' to strip trailing newlines.`,
+      range: mapRange(token.range),
+      severity: DiagnosticSeverity.Error,
+      code: "expression-block-scalar-chomping",
+      source: "github-actions"
+    });
+  }
+  // Error for number fields
+  else if (
+    defKey === "step-timeout-minutes" ||
+    (parentDefKey === "container-mapping" && key?.isScalar && ["ports", "volumes"].includes(key.toString())) ||
+    (parentDefKey === "job-factory" && key?.isScalar && key.toString() === "timeout-minutes")
+  ) {
+    diagnostics.push({
+      message: `Block scalar adds trailing newline which breaks number parsing. Use '${scalarIndicator}-' to strip trailing newlines.`,
+      range: mapRange(token.range),
+      severity: DiagnosticSeverity.Error,
+      code: "expression-block-scalar-chomping",
+      source: "github-actions"
+    });
+  }
+  // Error for specific string fields
+  else if (
+    defKey === "run-name" ||
+    defKey === "step-name" ||
+    defKey === "container" ||
+    defKey === "services-container" ||
+    defKey === "job-environment" ||
+    defKey === "job-environment-name" ||
+    defKey === "runs-on" ||
+    defKey === "runs-on-labels" ||
+    (parentDefKey === "container-mapping" && key?.isScalar && ["image", "credentials"].includes(key.toString())) ||
+    (parentDefKey === "job-defaults-run" && key?.isScalar && ["shell", "working-directory"].includes(key.toString())) ||
+    (parentDefKey === "job-environment-mapping" && key?.isScalar && key.toString() === "url") ||
+    (parentDefKey === "job-factory" && key?.isScalar && key.toString() === "name") ||
+    (parentDefKey === "workflow-job" && key?.isScalar && key.toString() === "name") ||
+    (parentDefKey === "run-step" && key?.isScalar && key.toString() === "working-directory") ||
+    (parentDefKey === "runs-on-mapping" && key?.isScalar && key.toString() === "group")
+  ) {
+    diagnostics.push({
+      message: `Block scalar adds trailing newline. Use '${scalarIndicator}-' to strip trailing newlines.`,
+      range: mapRange(token.range),
+      severity: DiagnosticSeverity.Error,
+      code: "expression-block-scalar-chomping",
+      source: "github-actions"
+    });
+  }
+  // Warning for everything else, but only on clip (default)
+  else if (token.chompStyle === "clip") {
+    diagnostics.push({
+      message: `Block scalar adds trailing newline to expression result. Use '${scalarIndicator}-' to strip or '${scalarIndicator}+' to keep trailing newlines.`,
+      range: mapRange(token.range),
+      severity: DiagnosticSeverity.Warning,
+      code: "expression-block-scalar-chomping",
+      source: "github-actions"
+    });
+  }
+}
@@ -200,4 +200,284 @@ jobs:
      throw new Error("expected if to be a basic expression");
    }
  });
+
+  describe("Block scalar chomp style preservation", () => {
+    it("preserves clip chomping (|) for literal block scalar", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("clip");
+    });
+
+    it("preserves strip chomping (|-) for literal block scalar", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |-
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("strip");
+    });
+
+    it("preserves keep chomping (|+) for literal block scalar", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |+
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("keep");
+    });
+
+    it("preserves folded clip (>) chomping", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: >
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_FOLDED");
+      expect(ifToken.chompStyle).toBe("clip");
+    });
+
+    it("preserves folded strip (>-) chomping", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: >-
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_FOLDED");
+      expect(ifToken.chompStyle).toBe("strip");
+    });
+
+    it("preserves with explicit indent (|2)", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |2
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("clip");
+    });
+
+    it("preserves with explicit indent and strip (|-2)", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |-2
+      \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("strip");
+    });
+
+    it("handles flow scalars (no chomp info for inline)", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: \${{ github.event_name == 'push' }}
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBeUndefined();
+      expect(ifToken.chompStyle).toBeUndefined();
+    });
+
+    it("handles job-if without ${{ }} (isExpression case)", () => {
+      const result = parseWorkflow(
+        {
+          name: "test.yaml",
+          content: `on: push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: |
+      github.event_name == 'push'
+    steps:
+      - run: echo hi`
+        },
+        nullTrace
+      );
+
+      expect(result.context.errors.getErrors()).toHaveLength(0);
+
+      const workflowRoot = result.value!.assertMapping("root")!;
+      const jobs = workflowRoot.get(1).value.assertMapping("jobs");
+      const build = jobs.get(0).value.assertMapping("job");
+      const ifToken = build.get(1).value;
+
+      if (!isBasicExpression(ifToken)) {
+        throw new Error("expected if to be a basic expression");
+      }
+
+      expect(ifToken.scalarType).toBe("BLOCK_LITERAL");
+      expect(ifToken.chompStyle).toBe("clip");
+    });
+  });
 });
@@ -1,6 +1,7 @@
 // template-reader *just* does schema validation
 /* eslint-disable @typescript-eslint/no-non-null-assertion */

+import {Scalar} from "yaml";
 import {ObjectReader} from "./object-reader";
 import {TemplateSchema} from "./schema";
 import {DefinitionInfo} from "./schema/definition-info";
@@ -459,7 +460,20 @@ class TemplateReader {
      // Doesn't contain "${{"
      // Check if value should still be evaluated as an expression
      if (definitionInfo.definition instanceof StringDefinition && definitionInfo.definition.isExpression) {
-        const expression = this.parseIntoExpressionToken(token.range!, raw, allowedContext, token, definitionInfo);
+        // For isExpression fields (e.g., 'if' conditions), parse token.value (not raw).
+        // Example YAML:
+        //   if: |
+        //     github.event_name == 'push'
+        // token.source/raw = "|\n  github.event_name == 'push'\n" (includes block scalar header)
+        // token.value = "github.event_name == 'push'\n" (clean expression content)
+        // We need token.value because the '|' would interfere with expression parsing.
+        const expression = this.parseIntoExpressionToken(
+          token.range!,
+          token.value,
+          allowedContext,
+          token,
+          definitionInfo
+        );
        if (expression) {
          return expression;
        }
@@ -606,13 +620,17 @@ class TemplateReader {
      }
    }

+    const blockScalarInfo = parseBlockScalarInfo(token);
    return new BasicExpressionToken(
      this._fileId,
      token.range,
      `format('${format.join("")}'${args.join("")})`,
      definitionInfo,
      expressionTokens,
-      raw
+      raw,
+      undefined,
+      blockScalarInfo.scalarType,
+      blockScalarInfo.chompStyle
    );
  }

@@ -686,6 +704,7 @@ class TemplateReader {
    };

    // Return the expression
+    const blockScalarInfo = parseBlockScalarInfo(token);
    return <ParseExpressionResult>{
      expression: new BasicExpressionToken(
        this._fileId,
@@ -694,7 +713,9 @@ class TemplateReader {
        definitionInfo,
        undefined,
        token.source,
-        expressionRange
+        expressionRange,
+        blockScalarInfo.scalarType,
+        blockScalarInfo.chompStyle
      ),
      error: undefined
    };
@@ -801,3 +822,53 @@ interface MatchDirectiveResult {
  parameters: string[];
  error: Error | undefined;
 }
+
+interface BlockScalarInfo {
+  scalarType: Scalar.Type | undefined;
+  chompStyle: "clip" | "strip" | "keep" | undefined;
+}
+
+/**
+ * Parse the block scalar info from the StringToken
+ * @param token The StringToken that may contain block scalar information
+ * @returns The scalar type and chomp style
+ */
+function parseBlockScalarInfo(token: StringToken): BlockScalarInfo {
+  const scalarType = token.scalarType;
+
+  // Only block scalars have chomp styles
+  if (scalarType !== Scalar.BLOCK_LITERAL && scalarType !== Scalar.BLOCK_FOLDED) {
+    return {scalarType: undefined, chompStyle: undefined};
+  }
+
+  // Parse chomp style from the block scalar header
+  // Look for block scalar indicators at the start: | or >
+  // Followed by optional chomp indicator (-, +) and/or explicit indent (digit)
+  // Examples: |, |-, |+, |2, |-2, |+2, >, >-, >+, >2, >-2, >+2
+  const header = token.blockScalarHeader;
+  if (!header) {
+    // If there's no header, assume clip (default)
+    return {scalarType, chompStyle: "clip"};
+  }
+
+  const blockScalarMatch = header.match(/^(\||>)([-+])?(\d)?/);
+
+  if (!blockScalarMatch) {
+    // Assume clip if we can't parse the indicator
+    return {scalarType, chompStyle: "clip"};
+  }
+
+  const chompIndicator = blockScalarMatch[2];
+
+  let chompStyle: "clip" | "strip" | "keep";
+  if (chompIndicator === "-") {
+    chompStyle = "strip";
+  } else if (chompIndicator === "+") {
+    chompStyle = "keep";
+  } else {
+    // No chomp indicator means clip (default)
+    chompStyle = "clip";
+  }
+
+  return {scalarType, chompStyle};
+}
@@ -1,3 +1,4 @@
+import {Scalar} from "yaml";
 import {DefinitionInfo} from "../schema/definition-info";

 import {CLOSE_EXPRESSION, OPEN_EXPRESSION} from "../template-constants";
@@ -23,6 +24,16 @@ export class BasicExpressionToken extends ExpressionToken {
   */
  public readonly expressionRange: TokenRange | undefined;

+  /**
+   * The YAML scalar type (e.g., BLOCK_LITERAL, BLOCK_FOLDED, PLAIN, etc.) if the expression was parsed from a block scalar.
+   */
+  public readonly scalarType: Scalar.Type | undefined;
+
+  /**
+   * The chomp style of the block scalar: 'clip' (default, keeps one newline), 'strip' (removes all), or 'keep' (keeps all).
+   */
+  public readonly chompStyle: "clip" | "strip" | "keep" | undefined;
+
  /**
   * @param originalExpressions If the basic expression was transformed from individual expressions, these will be the original ones
   */
@@ -33,13 +44,17 @@ export class BasicExpressionToken extends ExpressionToken {
    definitionInfo: DefinitionInfo | undefined,
    originalExpressions: BasicExpressionToken[] | undefined,
    source: string | undefined,
-    expressionRange?: TokenRange | undefined
+    expressionRange?: TokenRange | undefined,
+    scalarType?: Scalar.Type | undefined,
+    chompStyle?: "clip" | "strip" | "keep" | undefined
  ) {
    super(TokenType.BasicExpression, file, range, undefined, definitionInfo);
    this.expr = expression;
    this.source = source;
    this.originalExpressions = originalExpressions;
    this.expressionRange = expressionRange;
+    this.scalarType = scalarType;
+    this.chompStyle = chompStyle;
  }

  public get expression(): string {
@@ -55,7 +70,9 @@ export class BasicExpressionToken extends ExpressionToken {
          this.definitionInfo,
          this.originalExpressions,
          this.source,
-          this.expressionRange
+          this.expressionRange,
+          this.scalarType,
+          this.chompStyle
        )
      : new BasicExpressionToken(
          this.file,
@@ -64,7 +81,9 @@ export class BasicExpressionToken extends ExpressionToken {
          this.definitionInfo,
          this.originalExpressions,
          this.source,
-          this.expressionRange
+          this.expressionRange,
+          this.scalarType,
+          this.chompStyle
        );
  }

@@ -1,3 +1,4 @@
+import {Scalar} from "yaml";
 import {LiteralToken, TemplateToken} from ".";
 import {DefinitionInfo} from "../schema/definition-info";
 import {TokenRange} from "./token-range";
@@ -6,23 +7,45 @@ import {TokenType} from "./types";
 export class StringToken extends LiteralToken {
  public readonly value: string;
  public readonly source: string | undefined;
+  public readonly scalarType: Scalar.Type | undefined;
+  public readonly blockScalarHeader: string | undefined;

  public constructor(
    file: number | undefined,
    range: TokenRange | undefined,
    value: string,
    definitionInfo: DefinitionInfo | undefined,
-    source?: string
+    source?: string,
+    scalarType?: Scalar.Type,
+    blockScalarHeader?: string
  ) {
    super(TokenType.String, file, range, definitionInfo);
    this.value = value;
    this.source = source;
+    this.scalarType = scalarType;
+    this.blockScalarHeader = blockScalarHeader;
  }

  public override clone(omitSource?: boolean): TemplateToken {
    return omitSource
-      ? new StringToken(undefined, undefined, this.value, this.definitionInfo, this.source)
-      : new StringToken(this.file, this.range, this.value, this.definitionInfo, this.source);
+      ? new StringToken(
+          undefined,
+          undefined,
+          this.value,
+          this.definitionInfo,
+          this.source,
+          this.scalarType,
+          this.blockScalarHeader
+        )
+      : new StringToken(
+          this.file,
+          this.range,
+          this.value,
+          this.definitionInfo,
+          this.source,
+          this.scalarType,
+          this.blockScalarHeader
+        );
  }

  public override toString(): string {
@@ -117,11 +117,28 @@ export class YamlObjectReader implements ObjectReader {
        return new BooleanToken(fileId, range, value, undefined);
      case "string": {
        let source: string | undefined;
+        const scalarType = token.type;
+        let blockScalarHeader: string | undefined;
+
        if (token.srcToken && "source" in token.srcToken) {
          source = token.srcToken.source;
+          // Extract block scalar header. For example |-, |+, >-
+          //
+          // This relies on undocumented internal behavior (srcToken.props).
+          // Feature request for official support: https://github.com/eemeli/yaml/issues/643
+          if (token.srcToken.type === "block-scalar" && "props" in token.srcToken) {
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            const props = token.srcToken.props as any[];
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-unsafe-member-access
+            const headerProp = props.find((p: any) => p.type === "block-scalar-header");
+            if (headerProp && "source" in headerProp) {
+              // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment, @typescript-eslint/no-unsafe-member-access
+              blockScalarHeader = headerProp.source;
+            }
+          }
        }

-        return new StringToken(fileId, range, value, undefined, source);
+        return new StringToken(fileId, range, value, undefined, source, scalarType, blockScalarHeader);
      }
      default:
        throw new Error(`Unexpected value type '${typeof value}' when reading object`);