Only Run npm-package-json-lint When package.json is Present (#2280)

* Link to a PR rather than an issue in changelog

* Prefer list.append(x) to list += [x]

The former is slightly faster as it generally doesn't create a new list.

* Don't warn that REPOSITORY linters are missing

Some REPOSITORY linters are intentionally omitted from flavors to keep
their size small and performance fast. Hence, their absence from a
flavor isn't considered an error when FAIL_IF_MISSING_LINTER_IN_FLAVOR
is true. Therefore, omit them from the list of missing linters displayed
to the user to avoid confusion.

* Simplify check_active_linters_match_flavor

Reduce indentation by inverting test, and prefer the more Pythonic test
not list to len(list) == 0 for simplicity. Remove some comments rendered
unnecessary via this more direct expression of our intent.

* Correct capitalization of Docker in a warning

* Only lint package.json when present (#2279)

npm-package-json-lint only lints Node.js package.json files, so only run
it when package.json is present. npm-package-json-lint is correctly
omitted from most flavors. Many non-Node.js projects contain other JSON
files, so this change prevents false positives when
FAIL_IF_MISSING_LINTER_IN_FLAVOR is true.

Author: Kurt-von-Laven

CHANGELOG.md

@@ -16,7 +16,9 @@ Note: Can be used with `oxsecurity/megalinter@beta` in your GitHub Action mega-l
   - Change name of config file for powershell formatter to avoid collision with powershell linter config
   - Enhance find SARIF json in stdout output
   - Pass --show-context, --show-suggestions, and --no-must-find-files to CSpell for friendlier UX
-    by @Kurt-von-Laven in [#2271](https://github.com/oxsecurity/megalinter/issues/2271).
+    by @Kurt-von-Laven in [#2275](https://github.com/oxsecurity/megalinter/pull/2275).
+  - Only run npm-package-json-lint when package.json is present by @Kurt-von-Laven in
+    [#2280](https://github.com/oxsecurity/megalinter/pull/2280).
 
 - Documentation
   - Configure jsonschema documentation formatting (see [Descriptor schema](https://megalinter.io/latest/json-schemas/descriptor.html), [Configuration schema](https://megalinter.io/latest/json-schemas/configuration.html)), by @echoix in [#2270](https://github.com/oxsecurity/megalinter/pull/2270)

megalinter/descriptors/json.megalinter-descriptor.yml

@@ -233,6 +233,8 @@ linters:
       - salesforce
     file_names_regex:
       - "package\\.json"
+    active_only_if_file_found:
+      - "package.json"
     cli_lint_mode: project
     cli_executable: npmPkgJsonLint
     cli_config_arg_name: --configFile

megalinter/flavor_factory.py

@@ -84,31 +84,31 @@ def check_active_linters_match_flavor(active_linters):
     missing_linters = []
     for active_linter in active_linters:
         if active_linter.name not in flavor_linters:
-            missing_linters += [active_linter.name]
             active_linter.is_active = False
-    # Manage cases where linters are missing in flavor
-    if len(missing_linters) > 0:
-        # Do not warn/stop if missing linters are repository ones (mostly OX.security related)
-        if not are_all_repository_linters(missing_linters):
-            missing_linters_str = ",".join(missing_linters)
-            logging.warning(
-                f"MegaLinter flavor [{flavor}] does not contain linters {missing_linters_str}.\n"
-                "As they are not available in this docker image, they will not be processed\n"
-                "To solve this problem, please either: \n"
-                f"- use default flavor {ML_REPO}\n"
-                "- add ignored linters in DISABLE or DISABLE_LINTERS variables in your .mega-linter.yml config file "
-                "located in your root directory\n"
-                "- ignore this message by setting config variable FLAVOR_SUGGESTIONS to false"
-            )
-            # Stop the process if user wanted so in case of missing linters
-            if config.get("FAIL_IF_MISSING_LINTER_IN_FLAVOR", "") == "true":
-                logging.error(
-                    'Missing linter and FAIL_IF_MISSING_LINTER_IN_FLAVOR has been set to "true": Stop run'
-                )
-                sys.exit(84)
-        return False
-    # All good !
-    return True
+            # Ignore linters that shouldn't trigger failure when missing.
+            if not active_linter.name.startswith("REPOSITORY"):
+                missing_linters.append(active_linter.name)
+
+    if not missing_linters:
+        return True
+
+    missing_linters_str = ",".join(missing_linters)
+    logging.warning(
+        f"MegaLinter flavor [{flavor}] does not contain linters {missing_linters_str}.\n"
+        "As they are not available in this Docker image, they will not be processed\n"
+        "To solve this problem, please either: \n"
+        f"- use default flavor {ML_REPO}\n"
+        "- add ignored linters in DISABLE or DISABLE_LINTERS variables in your .mega-linter.yml config file "
+        "located in your root directory\n"
+        "- ignore this message by setting config variable FLAVOR_SUGGESTIONS to false"
+    )
+    # Stop the process if user wanted so in case of missing linters
+    if config.get("FAIL_IF_MISSING_LINTER_IN_FLAVOR", "") == "true":
+        logging.error(
+            'Missing linter and FAIL_IF_MISSING_LINTER_IN_FLAVOR has been set to "true": Stop run'
+        )
+        sys.exit(84)
+    return False
 
 
 # Compare active linters with available flavors to make suggestions to improve CI performances
@@ -147,13 +147,3 @@ def get_megalinter_flavor_suggestions(active_linters):
     )
     new_flavor_linters_names = map(lambda linter: linter.name, new_flavor_linters)
     return ["new", new_flavor_linters_names]
-
-
-def are_all_repository_linters(linter_names: list[str]) -> bool:
-    if len(linter_names) == 0:
-        return False
-    result = True
-    for linter_name in linter_names:
-        if not linter_name.startswith("REPOSITORY"):
-            result = False
-    return result