Fix corner-case in stdlib linting

conda_smithy/linter/lints.py

@@ -796,8 +796,15 @@ def flatten_reqs(reqs):
     # this check needs to be done per output --> use separate (unflattened) requirements
     for build_reqs in all_build_reqs:
         has_compiler = any(pat_compiler_stub.match(rq) for rq in build_reqs)
-        stdlib_stub = "c_stdlib_stub" if recipe_version == 0 else "${{ stdlib"
-        if has_compiler and stdlib_stub not in build_reqs:
+        stdlib_regex = (
+            # we need the C stdlib, not just any invocation of the stdlib jinja
+            "c_stdlib_stub"
+            if recipe_version == 0
+            else r"\$\{\{ stdlib\(['\"]c['\"]"
+        )
+        if has_compiler and not any(
+            re.search(stdlib_regex, x) for x in build_reqs
+        ):
             if stdlib_lint not in lints:
                 lints.append(stdlib_lint)
 

news/2041-stdlib_corner_case.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* Fixed a corner-case in stdlib-linting (#2042)
+
+**Security:**
+
+* <news item>

tests/test_lint_recipe.py

@@ -74,6 +74,27 @@ def test_stdlib_lint(comp_lang):
         assert any(lint.startswith(expected_message) for lint in lints)
 
 
+def test_m2w64_stdlib_legal():
+    # allow recipes that _only_ depend on {{ stdlib("m2w64_c") }}
+    avoid_message = "This recipe is using a compiler"
+
+    with tmp_directory() as recipe_dir:
+        with open(os.path.join(recipe_dir, "meta.yaml"), "w") as fh:
+            fh.write(
+                """
+                package:
+                   name: foo
+                requirements:
+                  build:
+                    - {{ stdlib("m2w64_c") }}
+                    - {{ compiler("m2w64_c") }}
+                """
+            )
+
+        lints, _ = linter.main(recipe_dir, return_hints=True)
+        assert not any(lint.startswith(avoid_message) for lint in lints)
+
+
 @pytest.mark.parametrize(
     "comp_lang",
     ["c", "cxx", "fortran", "rust", "m2w64_c", "m2w64_cxx", "m2w64_fortran"],