Add language service support for action.yml files (#275)

- Add validation, completion, hover, and document links for action.yml files
- Implement document type detection to route action.yml to action-specific handlers
- Add expression context for composite actions (inputs, steps, github, runner, etc.)
- Add schema validation for required fields, branding, and composite step requirements
- Support JavaScript (node20/node24), Docker, and composite action types
- Validate action references in composite action uses steps
- Add JSDoc comments to parser and template functions
- Refactor hover to use hoverToken consistently
- Fix lint errors and add return type annotations

languageservice/src/validate-action-reference.ts

@@ -0,0 +1,103 @@
+import {isMapping} from "@actions/workflow-parser";
+import {isActionStep} from "@actions/workflow-parser/model/type-guards";
+import {Step} from "@actions/workflow-parser/model/workflow-template";
+import {ScalarToken} from "@actions/workflow-parser/templates/tokens/scalar-token";
+import {TemplateToken} from "@actions/workflow-parser/templates/tokens/template-token";
+import {Diagnostic, DiagnosticSeverity} from "vscode-languageserver-types";
+import {parseActionReference} from "./action.js";
+import {mapRange} from "./utils/range.js";
+import {ValidationConfig} from "./validate.js";
+
+/**
+ * Validates action references in workflow steps, checking for valid inputs and required inputs.
+ */
+export async function validateActionReference(
+  diagnostics: Diagnostic[],
+  stepToken: TemplateToken,
+  step: Step | undefined,
+  config: ValidationConfig | undefined
+): Promise<void> {
+  if (!isMapping(stepToken) || !step || !isActionStep(step) || !config?.actionsMetadataProvider) {
+    return;
+  }
+
+  // Parse the action reference (e.g., "actions/checkout@v4" -> {owner, name, ref})
+  const action = parseActionReference(step.uses.value);
+  if (!action) {
+    return;
+  }
+
+  // Fetch the action's metadata (action.yml) to get input definitions
+  const actionMetadata = await config.actionsMetadataProvider.fetchActionMetadata(action);
+  if (actionMetadata === undefined) {
+    diagnostics.push({
+      severity: DiagnosticSeverity.Error,
+      range: mapRange(step.uses.range),
+      message: `Unable to resolve action \`${step.uses.value}\`, repository or version not found`
+    });
+    return;
+  }
+
+  // Find the "with" key in the step token to get the inputs passed to the action
+  let withKey: ScalarToken | undefined;
+  let withToken: TemplateToken | undefined;
+  for (const {key, value} of stepToken) {
+    if (key.toString() === "with") {
+      withKey = key;
+      withToken = value;
+      break;
+    }
+  }
+
+  // Collect the inputs provided in the step's "with" block
+  const stepInputs = new Map<string, ScalarToken>();
+  if (withToken && isMapping(withToken)) {
+    for (const {key} of withToken) {
+      stepInputs.set(key.toString(), key);
+    }
+  }
+
+  // Skip validation if the action doesn't define any inputs
+  const actionInputs = actionMetadata.inputs;
+  if (actionInputs === undefined) {
+    return;
+  }
+
+  // Check each provided input is valid and not deprecated
+  for (const [input, inputToken] of stepInputs) {
+    if (!actionInputs[input]) {
+      diagnostics.push({
+        severity: DiagnosticSeverity.Error,
+        range: mapRange(inputToken.range),
+        message: `Invalid action input '${input}'`
+      });
+    }
+
+    const deprecationMessage = actionInputs[input]?.deprecationMessage;
+    if (deprecationMessage) {
+      diagnostics.push({
+        severity: DiagnosticSeverity.Warning,
+        range: mapRange(inputToken.range),
+        message: deprecationMessage
+      });
+    }
+  }
+
+  // Check for required inputs that weren't provided and don't have defaults
+  const missingRequiredInputs = Object.entries(actionInputs).filter(
+    ([inputName, input]) => input.required && !stepInputs.has(inputName) && input.default === undefined
+  );
+
+  // Report missing required inputs
+  if (missingRequiredInputs.length > 0) {
+    const message =
+      missingRequiredInputs.length === 1
+        ? `Missing required input \`${missingRequiredInputs[0][0]}\``
+        : `Missing required inputs: ${missingRequiredInputs.map(input => `\`${input[0]}\``).join(", ")}`;
+    diagnostics.push({
+      severity: DiagnosticSeverity.Error,
+      range: mapRange((withKey || stepToken).range), // Highlight the whole step if we don't have a with key
+      message: message
+    });
+  }
+}