feat: group format messages into one

src/analyze/publint.ts

@@ -1,7 +1,26 @@
 import {publint} from 'publint';
 import {formatMessage} from 'publint/utils';
+import type {Message as PublintMessage} from 'publint';
 import type {ReportPluginResult, AnalysisContext} from '../types.js';
 
+type FormatMessage = Extract<
+  PublintMessage,
+  {code: 'FILE_INVALID_FORMAT' | 'FILE_INVALID_EXPLICIT_FORMAT'}
+>;
+
+function groupFormatMessages(messages: FormatMessage[]): string {
+  const [first] = messages;
+  const count = messages.length;
+  const {actualFormat, expectFormat, actualExtension, expectExtension} =
+    first.args;
+
+  if (first.code === 'FILE_INVALID_EXPLICIT_FORMAT') {
+    return `${count} files end with the ${actualExtension} extension, but the code is written in ${actualFormat}. Consider using the ${expectExtension} extension.`;
+  }
+
+  return `${count} files are written in ${actualFormat}, but are interpreted as ${expectFormat}. Consider using the ${expectExtension} extension.`;
+}
+
 export async function runPublint(
   context: AnalysisContext
 ): Promise<ReportPluginResult> {
@@ -11,14 +30,46 @@ export async function runPublint(
 
   try {
     const publintResult = await publint({pack: 'auto', pkgDir: context.root});
+
+    const groups = new Map<string, FormatMessage[]>();
     for (const problem of publintResult.messages) {
+      if (
+        problem.code === 'FILE_INVALID_FORMAT' ||
+        problem.code === 'FILE_INVALID_EXPLICIT_FORMAT'
+      ) {
+        const {actualFormat, expectFormat, expectExtension} = problem.args;
+        const key = `${problem.code}:${actualFormat}:${expectFormat}:${expectExtension}`;
+        const group = groups.get(key);
+        if (group) {
+          group.push(problem);
+        } else {
+          groups.set(key, [problem]);
+        }
+        continue;
+      }
+
       result.messages.push({
         severity: problem.type,
         score: 0,
         file: 'package.json',
         message: formatMessage(problem, publintResult.pkg) ?? ''
       });
     }
+
+    for (const group of groups.values()) {
+      const [first] = group;
+      const message =
+        group.length === 1
+          ? (formatMessage(first, publintResult.pkg) ?? '')
+          : groupFormatMessages(group);
+
+      result.messages.push({
+        severity: first.type,
+        score: 0,
+        file: 'package.json',
+        message
+      });
+    }
   } catch (error) {
     console.error(`Failed to run publint: ${error}`);
   }

src/test/analyze/publint.test.ts

@@ -0,0 +1,53 @@
+import {describe, it, expect} from 'vitest';
+import path from 'node:path';
+import {runPublint} from '../../analyze/publint.js';
+import {LocalFileSystem} from '../../local-file-system.js';
+import type {AnalysisContext} from '../../types.js';
+
+function makeContext(root: string): AnalysisContext {
+  return {
+    fs: new LocalFileSystem(root),
+    root,
+    messages: [],
+    stats: {
+      name: 'test-package',
+      version: '1.0.0',
+      dependencyCount: {production: 0, development: 0},
+      extraStats: []
+    },
+    lockfile: {
+      type: 'npm',
+      packages: [],
+      root: {
+        name: 'test-package',
+        version: '1.0.0',
+        dependencies: [],
+        devDependencies: [],
+        optionalDependencies: [],
+        peerDependencies: []
+      }
+    },
+    packageFile: {
+      name: 'test-package',
+      version: '1.0.0'
+    }
+  };
+}
+
+describe('runPublint', () => {
+  it('groups per-file format warnings into a single message', async () => {
+    const fixture = path.join(__dirname, '../../../test/fixtures/lazy-esm-cjs');
+
+    const result = await runPublint(makeContext(fixture));
+
+    const formatMessages = result.messages.filter((m) =>
+      m.message.includes('are interpreted as')
+    );
+
+    expect(formatMessages).toHaveLength(1);
+    expect(formatMessages[0]?.severity).toBe('warning');
+    expect(formatMessages[0]?.message).toBe(
+      '4 files are written in ESM, but are interpreted as CJS. Consider using the .mjs extension.'
+    );
+  });
+});

test/fixtures/lazy-esm-cjs/a.js

@@ -0,0 +1 @@
+export const a = 1;

test/fixtures/lazy-esm-cjs/b.js

@@ -0,0 +1 @@
+export const b = 2;

test/fixtures/lazy-esm-cjs/c.js

@@ -0,0 +1 @@
+export const c = 3;

test/fixtures/lazy-esm-cjs/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "lazy-esm-cjs",
+  "version": "1.0.0",
+  "type": "commonjs",
+  "main": "./a.js"
+}