feat(logger): add opt-in multi-line log alignment

preview/index.ts

@@ -1,4 +1,4 @@
-import { logger } from '../dist/index.js';
+import { createLogger, logger } from '../dist/index.js';
 import { getErrorCause } from './cause.ts';
 
 logger.greet(`\n➜ Rslog v1.0.0\n`);
@@ -16,3 +16,32 @@ logger.error(
     cause: getErrorCause(),
   }),
 );
+
+// multi-line alignment demo
+const alignLogger = createLogger({ alignMultiline: true });
+const prefixAlignLogger = createLogger({
+  alignMultiline: true,
+  prefix: '[web]',
+});
+
+alignLogger.info(`User profile updated:
+- Name: John Doe
+- Email: john@example.com
+- Phone: +1234567890`);
+
+prefixAlignLogger.info(`User profile updated:
+- Name: John Doe
+- Email: john@example.com`);
+
+// error stacks stay top-aligned even with alignMultiline
+alignLogger.error(`Something failed:
+- reason A
+    at /rslog/foo/bar.js:29:0
+- reason B`);
+
+// pre-formatted JSON content (demonstrates the double-indent trade-off)
+alignLogger.info(`Config loaded:
+{
+  "port": 3000,
+  "host": "localhost"
+}`);

src/createLogger.ts

@@ -1,8 +1,10 @@
 import { boldMint, color } from './color.js';
 import { LOG_LEVEL, LOG_TYPES } from './constants.js';
-import { isErrorStackMessage } from './utils.js';
+import { isErrorStackMessage, stripAnsi } from './utils.js';
 import type { Options, LogMessage, Logger, LogMethods } from './types.js';
 
+const LABEL_WIDTH = 7;
+
 const normalizeErrorMessage = (err: Error) => {
   if (err.stack) {
     const [rawName, ...rest] = err.stack.split('\n');
@@ -14,7 +16,12 @@ const normalizeErrorMessage = (err: Error) => {
 };
 
 export const createLogger = (options: Options = {}) => {
-  const { level = 'info', prefix, console = globalThis.console } = options;
+  const {
+    level = 'info',
+    prefix,
+    console = globalThis.console,
+    alignMultiline,
+  } = options;
 
   let maxLevel = level;
 
@@ -32,8 +39,11 @@ export const createLogger = (options: Options = {}) => {
 
     const label = 'label' in logType ? logType.label : '';
     let text = '';
+    const hasLabel = Boolean(label);
+
+    const isErrorObject = message instanceof Error;
 
-    if (message instanceof Error) {
+    if (isErrorObject) {
       text += normalizeErrorMessage(message);
 
       const { cause } = message;
@@ -57,6 +67,21 @@ export const createLogger = (options: Options = {}) => {
       text = `${prefix} ${text}`;
     }
 
+    if (alignMultiline && hasLabel && !isErrorObject && text.includes('\n')) {
+      const indent = ' '.repeat(
+        LABEL_WIDTH + 1 + (prefix ? stripAnsi(prefix).length + 1 : 0),
+      );
+      const skipStack = level === 'error';
+      text = text
+        .split('\n')
+        .map((line, i) =>
+          i === 0 || line === '' || (skipStack && isErrorStackMessage(line))
+            ? line
+            : indent + line,
+        )
+        .join('\n');
+    }
+
     const method = level === 'error' || level === 'warn' ? level : 'log';
     console[method](label ? `${label} ${text}` : text, ...args);
   };

src/types.ts

@@ -29,6 +29,13 @@ export interface Options {
    * @default globalThis.console
    */
   console?: Pick<Console, 'log' | 'warn' | 'error'>;
+  /**
+   * Aligns continuation lines of multi-line messages to the first line's
+   * content column (label + prefix). Error object stacks keep their original
+   * top-aligned formatting.
+   * @default false
+   */
+  alignMultiline?: boolean;
 }
 
 export type LogMethods = keyof typeof LOG_TYPES;

src/utils.ts

@@ -1,5 +1,12 @@
+const ANSI_REGEXP = new RegExp(`${String.fromCharCode(27)}\\[[0-9;]*m`, 'g');
+
+export const stripAnsi = (text: string): string =>
+  text.replace(ANSI_REGEXP, '');
+
 const errorStackRegExp =
   /at [^\r\n]{0,200}(?::\d+:\d+[\s)]*|\(<anonymous>\)|\(index\s\d+\))$/;
 
-export const isErrorStackMessage = (message: string) =>
-  errorStackRegExp.test(message);
+export const isErrorStackMessage = (message: string) => {
+  const stripped = stripAnsi(message);
+  return errorStackRegExp.test(stripped);
+};

tests/__snapshots__/logger.test.ts.snap

@@ -1,5 +1,25 @@
 // Rstest Snapshot v1
 
+exports[`logger > should align multi-line messages to label + prefix column 1`] = `
+[
+  [
+    "info    [web] User profile updated:
+              - Name: John Doe
+              - Email: john@example.com",
+  ],
+]
+`;
+
+exports[`logger > should align multi-line messages when alignMultiline is enabled 1`] = `
+[
+  [
+    "info    User profile updated:
+        - Name: John Doe
+        - Email: john@example.com",
+  ],
+]
+`;
+
 exports[`logger > should create new logger with info level correctly 1`] = `
 [
   [
@@ -53,6 +73,17 @@ exports[`logger > should create new logger with warn level correctly 2`] = `
 ]
 `;
 
+exports[`logger > should keep error stacks top-aligned when alignMultiline is enabled 1`] = `
+[
+  [
+    "error   Something failed:
+        - reason A
+    at /rslog/foo/bar.js:29:0
+        - reason B",
+  ],
+]
+`;
+
 exports[`logger > should log as expected 1`] = `
 [
   [
@@ -102,6 +133,13 @@ exports[`logger > should log error with stack correctly 1`] = `
 "
 `;
 
+exports[`logger > should not align Error object output when alignMultiline is enabled 1`] = `
+"error       at /rslog/foo/bar.js:29:0
+
+  [cause]:     at /rslog/foo/bar.js:29:0
+"
+`;
+
 exports[`logger > should prepend prefix correctly 1`] = `
 [
   [

tests/logger.test.ts

@@ -267,4 +267,125 @@ describe('logger', () => {
       rs.resetModules();
     }
   });
+
+  test('should align multi-line messages when alignMultiline is enabled', () => {
+    console.log = rs.fn();
+    console.error = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    alignLogger.info(`User profile updated:
+- Name: John Doe
+- Email: john@example.com`);
+
+    expect(
+      (console.log as Mock).mock.calls.map((items) =>
+        items.map((item) => stripAnsi(item.toString())),
+      ),
+    ).toMatchSnapshot();
+  });
+
+  test('should align multi-line messages to label + prefix column', () => {
+    console.log = rs.fn();
+
+    const alignLogger = createLogger({
+      alignMultiline: true,
+      prefix: '[web]',
+    });
+
+    alignLogger.info(`User profile updated:
+- Name: John Doe
+- Email: john@example.com`);
+
+    expect(
+      (console.log as Mock).mock.calls.map((items) =>
+        items.map((item) => stripAnsi(item.toString())),
+      ),
+    ).toMatchSnapshot();
+  });
+
+  test('should keep error stacks top-aligned when alignMultiline is enabled', () => {
+    console.error = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    alignLogger.error(`Something failed:
+- reason A
+    at /rslog/foo/bar.js:29:0
+- reason B`);
+
+    expect(
+      (console.error as Mock).mock.calls.map((items) =>
+        items.map((item) => stripAnsi(item.toString())),
+      ),
+    ).toMatchSnapshot();
+  });
+
+  test('should not align Error object output when alignMultiline is enabled', () => {
+    console.error = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    const err = new Error('this is an error message with cause', {
+      cause: getErrorCause(),
+    });
+    err.stack = '    at /rslog/foo/bar.js:29:0';
+
+    alignLogger.error(err);
+
+    expect(
+      stripAnsi((console.error as Mock).mock.calls[0][0].toString()),
+    ).toMatchSnapshot();
+  });
+
+  test('should keep grayed error stack un-indented and colored when alignMultiline is enabled', () => {
+    console.error = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    alignLogger.error(`Something failed:
+    at /rslog/foo/bar.js:29:0
+- reason B`);
+
+    const raw = (console.error as Mock).mock.calls[0][0].toString();
+    const lines = raw.split('\n');
+
+    expect(lines[1]).toContain(String.fromCharCode(27));
+    expect(stripAnsi(lines[1]).startsWith('    at ')).toBe(true);
+    expect(stripAnsi(lines[2]).startsWith('        - reason B')).toBe(true);
+  });
+
+  test('should align stack-like lines in non-error levels (no stack exemption)', () => {
+    console.log = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    alignLogger.info(`Deploy summary:
+- deployed at server:443:8080
+- status: ok`);
+
+    const lines = stripAnsi(
+      (console.log as Mock).mock.calls[0][0].toString(),
+    ).split('\n');
+
+    expect(lines[0].startsWith('info    Deploy summary:')).toBe(true);
+    expect(lines[1].startsWith('        - deployed at server:443:8080')).toBe(
+      true,
+    );
+    expect(lines[2].startsWith('        - status: ok')).toBe(true);
+  });
+
+  test('should not add trailing whitespace on blank lines when alignMultiline is enabled', () => {
+    console.log = rs.fn();
+
+    const alignLogger = createLogger({ alignMultiline: true });
+
+    alignLogger.info(`Part 1
+
+Part 2`);
+
+    const lines = (console.log as Mock).mock.calls[0][0].toString().split('\n');
+
+    expect(lines[1]).toBe('');
+  });
 });