GitNexus/gitnexus/test/unit/esm-extension-resolution.test.ts

/**
 * Unit tests for TypeScript ESM .js extension resolution.
 *
 * TypeScript ESM requires imports to use .js extensions even when source
 * files are .ts. The resolver must map .js → .ts (and .jsx → .tsx,
 * .mjs → .mts, .cjs → .cts) when the literal .js file does not exist.
 */

import { describe, it, expect } from 'vitest';
import { resolveImportPath } from '../../src/core/ingestion/import-resolvers/standard.js';
import { stripJsExtension } from '../../src/core/ingestion/import-resolvers/standard.js';
import { buildSuffixIndex } from '../../src/core/ingestion/import-resolvers/utils.js';
import { SupportedLanguages } from 'gitnexus-shared';

function makeCtx(files: string[]) {
  // Match production normalization: only replace backslashes with forward slashes
  const normalized = files.map((f) => f.replace(/\\/g, '/'));
  const allFilesSet = new Set(files);
  const index = buildSuffixIndex(normalized, files);
  const cache = new Map<string, string | null>();
  return { files, normalized, allFilesSet, index, cache };
}

function resolve(
  currentFile: string,
  importPath: string,
  language: SupportedLanguages,
  ctx: ReturnType<typeof makeCtx>,
): string | null {
  return resolveImportPath(
    currentFile,
    importPath,
    ctx.allFilesSet,
    ctx.files,
    ctx.normalized,
    ctx.cache,
    language,
    null,
    ctx.index,
  );
}

describe('TypeScript ESM .js extension resolution', () => {
  it('resolves ./utils.js to ./utils.ts when .js does not exist', () => {
    const ctx = makeCtx(['src/index.ts', 'src/utils.ts']);
    const result = resolve('src/index.ts', './utils.js', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/utils.ts');
  });

  it('resolves ./component.jsx to ./component.tsx', () => {
    const ctx = makeCtx(['src/app.ts', 'src/component.tsx']);
    const result = resolve('src/app.ts', './component.jsx', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/component.tsx');
  });

  it('resolves ./config.mjs to ./config.mts', () => {
    const ctx = makeCtx(['src/index.ts', 'src/config.mts']);
    const result = resolve('src/index.ts', './config.mjs', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/config.mts');
  });

  it('resolves ./legacy.cjs to ./legacy.cts', () => {
    const ctx = makeCtx(['src/index.ts', 'src/legacy.cts']);
    const result = resolve('src/index.ts', './legacy.cjs', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/legacy.cts');
  });

  it('prefers actual .js file when it exists', () => {
    const ctx = makeCtx(['src/index.ts', 'src/utils.js', 'src/utils.ts']);
    const result = resolve('src/index.ts', './utils.js', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/utils.js');
  });

  it('resolves relative path with ../ and .js extension', () => {
    const ctx = makeCtx(['src/helpers/token.ts', 'src/core/engine.ts']);
    const result = resolve(
      'src/core/engine.ts',
      '../helpers/token.js',
      SupportedLanguages.TypeScript,
      ctx,
    );
    expect(result).toBe('src/helpers/token.ts');
  });

  it('works for JavaScript language too', () => {
    const ctx = makeCtx(['src/index.js', 'src/utils.ts']);
    const result = resolve('src/index.js', './utils.js', SupportedLanguages.JavaScript, ctx);
    expect(result).toBe('src/utils.ts');
  });

  it('does NOT apply ESM fallback for non-TS/JS languages', () => {
    const ctx = makeCtx(['src/main.py', 'src/utils.ts']);
    const result = resolve('src/main.py', './utils.js', SupportedLanguages.Python, ctx);
    expect(result).toBeNull();
  });

  it('returns null when neither .js nor .ts exists', () => {
    const ctx = makeCtx(['src/index.ts']);
    const result = resolve('src/index.ts', './missing.js', SupportedLanguages.TypeScript, ctx);
    expect(result).toBeNull();
  });
});

describe('ESM extension resolution — .mjs/.cjs with competing siblings', () => {
  it('resolves ./config.mjs to .ts when only .ts exists (no .mts)', () => {
    const ctx = makeCtx(['src/index.ts', 'src/config.ts']);
    const result = resolve('src/index.ts', './config.mjs', SupportedLanguages.TypeScript, ctx);
    // .ts wins because EXTENSIONS order tries .ts before .mts
    expect(result).toBe('src/config.ts');
  });

  it('resolves ./config.mjs to .mts when both .ts and .mts exist', () => {
    // Note: EXTENSIONS order is .tsx, .ts, .mts, .cts — so .ts wins over .mts.
    // This is intentional for a source-analysis tool: we resolve to the first
    // matching source file. In practice, having both config.ts and config.mts
    // in the same directory is extremely rare.
    const ctx = makeCtx(['src/index.ts', 'src/config.ts', 'src/config.mts']);
    const result = resolve('src/index.ts', './config.mjs', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/config.ts');
  });

  it('resolves ./config.cjs to .cts when only .cts exists', () => {
    const ctx = makeCtx(['src/index.ts', 'src/config.cts']);
    const result = resolve('src/index.ts', './config.cjs', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/config.cts');
  });
});

describe('ESM extension resolution — directory index boundary', () => {
  it('resolves ./dir.js to dir/index.ts when dir/ exists (bundler-mode)', () => {
    // After stripping .js from "dir.js" → "dir", tryResolveWithExtensions probes
    // "/index.ts" suffix. This matches bundler-mode behavior where bare directory
    // imports resolve to index files. Intentional for source-analysis compatibility.
    const ctx = makeCtx(['src/index.ts', 'src/dir/index.ts']);
    const result = resolve('src/index.ts', './dir.js', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/dir/index.ts');
  });

  it('resolves ./dir/index.js to dir/index.ts', () => {
    const ctx = makeCtx(['src/index.ts', 'src/dir/index.ts']);
    const result = resolve('src/index.ts', './dir/index.js', SupportedLanguages.TypeScript, ctx);
    expect(result).toBe('src/dir/index.ts');
  });
});

describe('stripJsExtension', () => {
  it('strips .js', () => expect(stripJsExtension('foo/bar.js')).toBe('foo/bar'));
  it('strips .jsx', () => expect(stripJsExtension('foo/bar.jsx')).toBe('foo/bar'));
  it('strips .mjs', () => expect(stripJsExtension('foo/bar.mjs')).toBe('foo/bar'));
  it('strips .cjs', () => expect(stripJsExtension('foo/bar.cjs')).toBe('foo/bar'));
  it('returns null for .ts', () => expect(stripJsExtension('foo/bar.ts')).toBeNull());
  it('returns null for no extension', () => expect(stripJsExtension('foo/bar')).toBeNull());
});

describe('ESM extension resolution — path aliases with .js extensions', () => {
  const aliasAtToSrc = new Map<string, string>([['@/', 'src/']]);
  const aliasTildeToSrc = new Map<string, string>([['~/', 'src/']]);

  function resolveWithAlias(
    currentFile: string,
    importPath: string,
    ctx: ReturnType<typeof makeCtx>,
    aliases: Map<string, string>,
    baseUrl = '.',
  ): string | null {
    return resolveImportPath(
      currentFile,
      importPath,
      ctx.allFilesSet,
      ctx.files,
      ctx.normalized,
      ctx.cache,
      SupportedLanguages.TypeScript,
      { aliases, baseUrl },
      ctx.index,
    );
  }

  it('resolves @/utils.js to src/utils.ts via alias', () => {
    const ctx = makeCtx(['src/index.ts', 'src/utils.ts']);
    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, aliasAtToSrc, '.');
    expect(result).toBe('src/utils.ts');
  });

  it('resolves @/component.jsx to src/component.tsx via alias', () => {
    const ctx = makeCtx(['src/index.ts', 'src/component.tsx']);
    const result = resolveWithAlias('src/index.ts', '@/component.jsx', ctx, aliasAtToSrc, '.');
    expect(result).toBe('src/component.tsx');
  });

  it('resolves @/config.mjs to src/config.mts via alias', () => {
    const ctx = makeCtx(['src/index.ts', 'src/config.mts']);
    const result = resolveWithAlias('src/index.ts', '@/config.mjs', ctx, aliasAtToSrc, '.');
    expect(result).toBe('src/config.mts');
  });

  it('resolves @/legacy.cjs to src/legacy.cts via alias', () => {
    const ctx = makeCtx(['src/index.ts', 'src/legacy.cts']);
    const result = resolveWithAlias('src/index.ts', '@/legacy.cjs', ctx, aliasAtToSrc, '.');
    expect(result).toBe('src/legacy.cts');
  });

  it('prefers actual .js file over TS fallback in alias resolution', () => {
    const ctx = makeCtx(['src/index.ts', 'src/utils.js', 'src/utils.ts']);
    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, aliasAtToSrc, '.');
    expect(result).toBe('src/utils.js');
  });

  it('resolves alias with baseUrl prefix', () => {
    const ctx = makeCtx(['app/src/index.ts', 'app/src/helpers/token.ts']);
    const result = resolveWithAlias(
      'app/src/index.ts',
      '~/helpers/token.js',
      ctx,
      aliasTildeToSrc,
      'app',
    );
    expect(result).toBe('app/src/helpers/token.ts');
  });

  it('returns null when alias .js import has no matching source', () => {
    const ctx = makeCtx(['src/index.ts']);
    const result = resolveWithAlias('src/index.ts', '@/missing.js', ctx, aliasAtToSrc, '.');
    expect(result).toBeNull();
  });
});