test(language/lint): add unit tests for unreachable-code pass

packages/language/src/lint/unreachable-code.test.ts

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2026, Salesforce, Inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ * For full license text, see the LICENSE file in the repo root or https://www.apache.org/licenses/LICENSE-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { parse } from '@agentscript/parser';
+import { Dialect } from '../core/dialect.js';
+import { NamedBlock, NamedCollectionBlock } from '../core/block.js';
+import { StringValue, ProcedureValue } from '../core/primitives.js';
+import { LintEngine } from '../core/analysis/lint-engine.js';
+import { createSchemaContext } from '../core/analysis/scope.js';
+import { unreachableCodePass } from './unreachable-code.js';
+
+const ProcBlock = NamedBlock('ProcBlock', {
+  label: StringValue.describe('Label'),
+  body: ProcedureValue.describe('Procedure body'),
+});
+
+const TestSchema = {
+  proc: NamedCollectionBlock(ProcBlock),
+};
+
+const schemaCtx = createSchemaContext({ schema: TestSchema, aliases: {} });
+
+function getDiagnostics(source: string) {
+  const { rootNode: root } = parse(source);
+  const mappingNode =
+    root.namedChildren.find(n => n.type === 'mapping') ?? root;
+
+  const dialect = new Dialect();
+  const result = dialect.parse(mappingNode, TestSchema);
+
+  const engine = new LintEngine({
+    passes: [unreachableCodePass()],
+    source: 'test',
+  });
+  const { diagnostics } = engine.run(result.value, schemaCtx);
+  return diagnostics.filter(d => d.code === 'unreachable-code');
+}
+
+describe('unreachable-code lint pass', () => {
+  it('flags code after a transition', () => {
+    const diags = getDiagnostics(`
+proc one:
+  label: "one"
+  body: ->
+    transition to @subagent.next
+    | this line is unreachable
+`);
+    expect(diags).toHaveLength(1);
+    expect(diags[0].message).toContain('transition');
+  });
+
+  it('does not flag a procedure whose last statement is a transition', () => {
+    const diags = getDiagnostics(`
+proc one:
+  label: "one"
+  body: ->
+    | greet the user
+    transition to @subagent.next
+`);
+    expect(diags).toHaveLength(0);
+  });
+
+  it('flags code after an if/else where both branches transition', () => {
+    const diags = getDiagnostics(`
+proc one:
+  label: "one"
+  body: ->
+    if @variables.x == "a":
+      transition to @subagent.left
+    else:
+      transition to @subagent.right
+    | this line is unreachable
+`);
+    expect(diags).toHaveLength(1);
+    expect(diags[0].message).toContain("'if'");
+  });
+
+  it('does not flag code after an if/else where only one branch transitions', () => {
+    const diags = getDiagnostics(`
+proc one:
+  label: "one"
+  body: ->
+    if @variables.x == "a":
+      transition to @subagent.left
+    else:
+      | stay here
+    | this line still runs in the else case
+`);
+    expect(diags).toHaveLength(0);
+  });
+
+  it('flags unreachable code inside a nested if body', () => {
+    const diags = getDiagnostics(`
+proc one:
+  label: "one"
+  body: ->
+    if @variables.x == "a":
+      transition to @subagent.left
+      | unreachable inside the if
+    | still reachable here
+`);
+    expect(diags).toHaveLength(1);
+  });
+});