fix(eslint-factory): exempt console.error/console.warn from prefer-core-logging

eslint-factory/README.md

@@ -26,6 +26,7 @@ This project hosts custom ESLint linters for `/actions/setup/js`.
 | [`no-unsafe-catch-error-property`](#no-unsafe-catch-error-property) | Disallow unsafe property access on `catch` error bindings |
 | [`no-unsafe-promise-catch-error-property`](#no-unsafe-promise-catch-error-property) | Disallow unsafe property access in promise rejection handlers |
 | [`prefer-get-error-message`](#prefer-get-error-message) | Prefer `getErrorMessage(err)` over the inline ternary pattern |
+| [`prefer-core-logging`](#prefer-core-logging) | Prefer `@actions/core` logging over `console.log` / `console.info` / `console.debug` |
 | [`prefer-number-isnan`](#prefer-number-isnan) | Prefer `Number.isNaN()` over global `isNaN()` |
 | [`require-async-entrypoint-catch`](#require-async-entrypoint-catch) | Require `.catch(...)` on bare async entrypoint calls |
 | [`require-await-core-summary-write`](#require-await-core-summary-write) | Require `await` on `core.summary.write()` calls |
@@ -382,3 +383,21 @@ Why: when `spawnSync` cannot spawn the child process (e.g. `ENOENT`, `ETIMEDOUT`
 - Passing the result object to a helper function that internally checks `.error` is not recognized.
 - Mutable aliases (`let e = result.error; e = undefined; if (e) throw e`) are rejected because the original value may have been discarded before the guard.
 
+### `prefer-core-logging`
+
+Prefer `@actions/core` logging methods (`core.info`, `core.debug`) over `console.log`, `console.info`, and `console.debug`.
+
+`core.*` logging methods integrate with the GitHub Actions annotation system (errors and warnings appear as file annotations in the UI) and produce structured log output. `global.core` is always available via `shim.cjs` in the Node.js context and via `github-script` in the Actions context.
+
+**Covered methods and their replacements:**
+
+| `console.*` method | Suggested replacement |
+|---|---|
+| `console.log` | `core.info` |
+| `console.info` | `core.info` |
+| `console.debug` | `core.debug` |
+
+**Intentionally excluded: `console.error` and `console.warn`**
+
+`console.error` and `console.warn` write to **`process.stderr`**, while `core.error` and `core.warning` emit GitHub Actions workflow commands to **`process.stdout`**. For processes that own stdout as a data/protocol channel — such as stdio MCP servers and transports — replacing stderr logging with stdout logging would corrupt the JSON-RPC stream. Because the stream change is not behavior-preserving, the rule never reports `console.error` or `console.warn` and offers no suggestion to replace them.
+

eslint-factory/src/rules/prefer-core-logging.test.ts

@@ -28,16 +28,6 @@ describe("prefer-core-logging", () => {
             { messageId: "preferCoreLogging", data: { method: "log", replacement: "core.info" }, suggestions: [{ messageId: "replaceWithCoreMethod", data: { replacement: "core.info", args: `"hello"` }, output: `core.info("hello");` }] },
           ],
         },
-        {
-          code: `console.error("bad thing");`,
-          errors: [
-            {
-              messageId: "preferCoreLogging",
-              data: { method: "error", replacement: "core.error" },
-              suggestions: [{ messageId: "replaceWithCoreMethod", data: { replacement: "core.error", args: `"bad thing"` }, output: `core.error("bad thing");` }],
-            },
-          ],
-        },
         {
           code: `const foo = "bar"; console.log(foo);`,
           errors: [
@@ -100,39 +90,29 @@ describe("prefer-core-logging", () => {
     });
   });
 
-  it("invalid: console.error when core is in scope", () => {
+  it("valid: console.error is not flagged — writes to stderr, not stdout", () => {
     ruleTester.run("prefer-core-logging", preferCoreLoggingRule, {
-      valid: [],
-      invalid: [
-        {
-          code: `const core = require("@actions/core"); console.error("bad thing");`,
-          errors: [
-            {
-              messageId: "preferCoreLogging",
-              data: { method: "error", replacement: "core.error" },
-              suggestions: [{ messageId: "replaceWithCoreMethod", data: { replacement: "core.error", args: `"bad thing"` }, output: `const core = require("@actions/core"); core.error("bad thing");` }],
-            },
-          ],
-        },
+      valid: [
+        // console.error writes to stderr; core.error writes workflow commands to stdout.
+        // Replacing stderr logging with stdout logging would corrupt stdio-protocol
+        // channels (e.g. MCP servers), so the rule intentionally exempts console.error.
+        `console.error("bad thing");`,
+        `const core = require("@actions/core"); console.error("bad thing");`,
+        `console.error("MCP transport error:", new Error("oops"));`,
       ],
+      invalid: [],
     });
   });
 
-  it("invalid: console.warn when core is in scope", () => {
+  it("valid: console.warn is not flagged — writes to stderr, not stdout", () => {
     ruleTester.run("prefer-core-logging", preferCoreLoggingRule, {
-      valid: [],
-      invalid: [
-        {
-          code: `const core = require("@actions/core"); console.warn("warning");`,
-          errors: [
-            {
-              messageId: "preferCoreLogging",
-              data: { method: "warn", replacement: "core.warning" },
-              suggestions: [{ messageId: "replaceWithCoreMethod", data: { replacement: "core.warning", args: `"warning"` }, output: `const core = require("@actions/core"); core.warning("warning");` }],
-            },
-          ],
-        },
+      valid: [
+        // console.warn writes to stderr; core.warning writes workflow commands to stdout.
+        // Same stream-semantics rationale as console.error above.
+        `console.warn("warning");`,
+        `const core = require("@actions/core"); console.warn("warning");`,
       ],
+      invalid: [],
     });
   });
 

eslint-factory/src/rules/prefer-core-logging.ts

@@ -2,12 +2,16 @@ import { AST_NODE_TYPES, ESLintUtils, TSESTree } from "@typescript-eslint/utils"
 
 const createRule = ESLintUtils.RuleCreator(name => `https://github.com/github/gh-aw/tree/main/eslint-factory#${name}`);
 
-// Maps console method → recommended core replacement
+// Maps console method → recommended core replacement.
+// NOTE: console.error and console.warn are intentionally excluded.
+// Those methods write to process.stderr, while core.error / core.warning emit
+// GitHub Actions workflow commands to process.stdout. For processes that own
+// stdout as a data/protocol channel (e.g. stdio MCP servers), rewriting
+// stderr logging to stdout would corrupt the stream. The substitution is not
+// behavior-preserving and must not be auto-applied.
 const CONSOLE_TO_CORE: Record<string, string> = {
   log: "core.info",
   info: "core.info",
-  warn: "core.warning",
-  error: "core.error",
   debug: "core.debug",
 };