fix: install @babel/preset-typescript for TypeScript transformation when only Babel is available

codeflash/languages/javascript/test_runner.py

@@ -219,6 +219,150 @@ def _has_ts_jest_dependency(project_root: Path) -> bool:
         return False
 
 
+def _ensure_babel_preset_typescript(project_root: Path) -> bool:
+    """Ensure @babel/preset-typescript is installed if @babel/core is present.
+
+    Args:
+        project_root: Root of the project.
+
+    Returns:
+        True if @babel/preset-typescript is available (already installed or just installed),
+        False if installation failed or @babel/core is not present.
+
+    """
+    package_json = project_root / "package.json"
+    if not package_json.exists():
+        return False
+
+    try:
+        content = json.loads(package_json.read_text())
+        deps = {**content.get("dependencies", {}), **content.get("devDependencies", {})}
+
+        # Only proceed if @babel/core is installed
+        if "@babel/core" not in deps:
+            return False
+
+        # Check if already available
+        if "@babel/preset-typescript" in deps:
+            return True
+
+        # Check if actually resolvable (might be transitively installed)
+        check_cmd = [
+            "node",
+            "-e",
+            "try { require.resolve('@babel/preset-typescript'); process.exit(0); } catch { process.exit(1); }",
+        ]
+        result = subprocess.run(check_cmd, cwd=project_root, capture_output=True, timeout=5, check=False)
+        if result.returncode == 0:
+            logger.debug("@babel/preset-typescript available transitively")
+            return True
+
+        # Not available - install it
+        logger.info("Installing @babel/preset-typescript for TypeScript transformation...")
+        install_cmd = get_package_install_command(project_root, "@babel/preset-typescript", dev=True)
+        result = subprocess.run(install_cmd, check=False, cwd=project_root, capture_output=True, text=True, timeout=120)
+
+        if result.returncode == 0:
+            logger.debug(f"Installed @babel/preset-typescript using {install_cmd[0]}")
+            return True
+
+        logger.warning(f"Failed to install @babel/preset-typescript: {result.stderr}")
+        return False
+
+    except Exception as e:
+        logger.warning(f"Error ensuring @babel/preset-typescript: {e}")
+        return False
+
+
+def _detect_typescript_transformer(project_root: Path) -> tuple[str | None, str]:
+    """Detect the TypeScript transformer configured in the project.
+
+    Checks package.json for common TypeScript transformers and returns
+    the transformer name and its configuration string for Jest config.
+
+    If no transformer is found but @babel/core is installed, attempts to
+    install @babel/preset-typescript and returns a babel-jest config.
+
+    Args:
+        project_root: Root of the project.
+
+    Returns:
+        Tuple of (transformer_name, config_string) where:
+        - transformer_name is the package name (e.g., "@swc/jest", "ts-jest")
+        - config_string is the Jest transform config snippet to inject
+        Returns (None, "") if no TypeScript transformer is found.
+
+    """
+    package_json = project_root / "package.json"
+    if not package_json.exists():
+        return (None, "")
+
+    try:
+        content = json.loads(package_json.read_text())
+        deps = {**content.get("dependencies", {}), **content.get("devDependencies", {})}
+
+        # Check for various TypeScript transformers in order of preference
+        if "ts-jest" in deps:
+            config = """
+  // Ensure TypeScript files are transformed using ts-jest
+  transform: {
+    '^.+\\\\.(ts|tsx)$': ['ts-jest', { isolatedModules: true }],
+    // Use ts-jest for JS files in ESM packages too
+    '^.+\\\\.js$': ['ts-jest', { isolatedModules: true }],
+  },"""
+            return ("ts-jest", config)
+
+        if "@swc/jest" in deps:
+            config = """
+  // Ensure TypeScript files are transformed using @swc/jest
+  transform: {
+    '^.+\\\\.(ts|tsx)$': '@swc/jest',
+  },"""
+            return ("@swc/jest", config)
+
+        if "babel-jest" in deps and "@babel/preset-typescript" in deps:
+            config = """
+  // Ensure TypeScript files are transformed using babel-jest
+  transform: {
+    '^.+\\\\.(ts|tsx)$': 'babel-jest',
+  },"""
+            return ("babel-jest", config)
+
+        if "esbuild-jest" in deps:
+            config = """
+  // Ensure TypeScript files are transformed using esbuild-jest
+  transform: {
+    '^.+\\\\.(ts|tsx)$': 'esbuild-jest',
+  },"""
+            return ("esbuild-jest", config)
+
+        # Fallback: If @babel/core is installed but no TypeScript transformer found,
+        # try to ensure @babel/preset-typescript is available and use babel-jest.
+        # This handles projects that have Babel but no TypeScript-specific setup.
+        if "@babel/core" in deps:
+            # Ensure preset-typescript is available (install if needed)
+            if _ensure_babel_preset_typescript(project_root):
+                config = """
+  // Fallback: Use babel-jest with TypeScript preset
+  // @babel/preset-typescript was installed by codeflash for TypeScript transformation
+  transform: {
+    '^.+\\\\.(ts|tsx)$': ['babel-jest', {
+      presets: [
+        ['@babel/preset-typescript', { allowDeclareFields: true }]
+      ]
+    }],
+  },"""
+                return ("babel-jest (fallback)", config)
+            logger.warning(
+                "@babel/core is installed but @babel/preset-typescript could not be installed. "
+                "TypeScript files may fail to transform. Consider installing ts-jest or @swc/jest."
+            )
+
+        return (None, "")
+    except (json.JSONDecodeError, OSError):
+        return (None, "")
+
+
 def _create_codeflash_jest_config(
     project_root: Path, original_jest_config: Path | None, *, for_esm: bool = False
 ) -> Path | None:
@@ -278,21 +422,13 @@ def _create_codeflash_jest_config(
     ]
     esm_pattern = "|".join(esm_packages)
 
-    # Check if ts-jest is available in the project
-    has_ts_jest = _has_ts_jest_dependency(project_root)
+    # Detect TypeScript transformer in the project
+    transformer_name, transform_config = _detect_typescript_transformer(project_root)
 
-    # Build transform config only if ts-jest is available
-    if has_ts_jest:
-        transform_config = """
-  // Ensure TypeScript files are transformed using ts-jest
-  transform: {
-    '^.+\\\\.(ts|tsx)$': ['ts-jest', { isolatedModules: true }],
-    // Use ts-jest for JS files in ESM packages too
-    '^.+\\\\.js$': ['ts-jest', { isolatedModules: true }],
-  },"""
+    if transformer_name:
+        logger.debug(f"Detected TypeScript transformer: {transformer_name}")
     else:
-        transform_config = ""
-        logger.debug("ts-jest not found in project dependencies, skipping transform config")
+        logger.debug("No TypeScript transformer found in project dependencies")
 
     # Create a wrapper Jest config
     if original_jest_config:

tests/test_languages/test_typescript_babel_fallback.py

@@ -0,0 +1,167 @@
+"""Test that TypeScript files can be transformed when Babel is installed but no TS transformer exists.
+
+This tests the fix for the bug where projects with @babel/core but no TypeScript
+transformer would fail with "experimental syntax 'flow'" error when Jest tried
+to transform TypeScript files.
+
+Related trace IDs: 26117bae-39bb-4f2f-9047-f2eb6594b7eb, and 3 others
+"""
+import json
+import tempfile
+from pathlib import Path
+import pytest
+
+
+def test_typescript_transform_with_babel_no_preset():
+    """
+    Test that _detect_typescript_transformer() returns a working config
+    when @babel/core is present but no TypeScript transformer is installed.
+
+    This fixes the bug where Jest would use babel-jest by default (when @babel/core
+    is installed) but fail to transform TypeScript because Babel didn't have
+    preset-typescript configured.
+    """
+    from codeflash.languages.javascript.test_runner import _detect_typescript_transformer
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        project_root = Path(tmpdir)
+
+        # Create a package.json with @babel/core but no TS transformer
+        package_json = {
+            "name": "test-project",
+            "devDependencies": {
+                "@babel/core": "^7.22.5",
+                "@babel/preset-env": "^7.22.5",
+                # NO ts-jest, @swc/jest, @babel/preset-typescript, or esbuild-jest
+            }
+        }
+        (project_root / "package.json").write_text(json.dumps(package_json))
+
+        # Test the detection
+        transformer_name, transform_config = _detect_typescript_transformer(project_root)
+
+        # With the fix: should return babel-jest with inline preset-typescript
+        assert transformer_name == "babel-jest (fallback)"
+        assert transform_config != ""
+        assert "babel-jest" in transform_config
+        assert "@babel/preset-typescript" in transform_config
+        assert "\\.(ts|tsx)" in transform_config or r"\.(ts|tsx)" in transform_config
+
+
+def test_generated_jest_config_handles_typescript_with_babel():
+    """
+    Test that the generated Jest config can transform TypeScript when only Babel is available.
+
+    This verifies the end-to-end fix: the config should include a transform
+    directive that uses babel-jest with preset-typescript.
+    """
+    from codeflash.languages.javascript.test_runner import _create_codeflash_jest_config
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        project_root = Path(tmpdir)
+
+        # Setup: project with @babel/core but no TS transformer
+        package_json = {
+            "name": "test-babel-ts",
+            "devDependencies": {
+                "@babel/core": "^7.22.5",
+                "@babel/preset-env": "^7.22.5",
+            }
+        }
+        (project_root / "package.json").write_text(json.dumps(package_json))
+
+        # Create a TypeScript source file (for realism, not used by config generation)
+        src_dir = project_root / "src"
+        src_dir.mkdir()
+        (src_dir / "example.ts").write_text("""
+export interface User {
+    name: string;
+    age: number;
+}
+
+export function greet(user: User): string {
+    return `Hello, ${user.name}!`;
+}
+""")
+
+        # Generate codeflash Jest config
+        config_path = _create_codeflash_jest_config(project_root, None, for_esm=False)
+
+        assert config_path is not None
+        assert config_path.exists()
+
+        config_content = config_path.read_text()
+
+        # The config should include a transform directive
+        assert "transform:" in config_content, (
+            "Generated Jest config must include a transform directive to handle "
+            "TypeScript files when @babel/core is installed"
+        )
+
+        # Should use babel-jest with preset-typescript
+        assert "babel-jest" in config_content
+        assert "@babel/preset-typescript" in config_content
+
+        # Should handle .ts and .tsx files (may be escaped as \. in regex)
+        assert "ts" in config_content and "tsx" in config_content
+
+
+def test_fallback_not_triggered_when_explicit_transformer_exists():
+    """
+    Test that the Babel fallback is NOT used when an explicit TypeScript transformer exists.
+
+    When ts-jest, @swc/jest, etc. are installed, those should take precedence.
+    """
+    from codeflash.languages.javascript.test_runner import _detect_typescript_transformer
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        project_root = Path(tmpdir)
+
+        # Project with both @babel/core AND ts-jest
+        package_json = {
+            "name": "test-project",
+            "devDependencies": {
+                "@babel/core": "^7.22.5",
+                "ts-jest": "^29.0.0",
+            }
+        }
+        (project_root / "package.json").write_text(json.dumps(package_json))
+
+        transformer_name, transform_config = _detect_typescript_transformer(project_root)
+
+        # Should prefer ts-jest over babel fallback
+        assert transformer_name == "ts-jest"
+        assert "ts-jest" in transform_config
+        assert "babel-jest" not in transform_config
+
+
+def test_no_transformer_when_babel_not_installed():
+    """
+    Test that no transformer is returned when neither Babel nor TypeScript transformers exist.
+
+    This ensures the fallback only triggers when @babel/core is present.
+    """
+    from codeflash.languages.javascript.test_runner import _detect_typescript_transformer
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        project_root = Path(tmpdir)
+
+        # Project with no transformers at all
+        package_json = {
+            "name": "test-project",
+            "devDependencies": {
+                "jest": "^29.0.0",
+                # NO @babel/core, NO ts-jest, etc.
+            }
+        }
+        (project_root / "package.json").write_text(json.dumps(package_json))
+
+        transformer_name, transform_config = _detect_typescript_transformer(project_root)
+
+        # Should return no transformer (Jest will use default behavior)
+        assert transformer_name is None
+        assert transform_config == ""
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])