Fix cppstd_compat migration for 2.12

conan/api/subapi/config.py

@@ -208,7 +208,7 @@ def clean(self):
         packages_folder = self.global_conf.get("core.cache:storage_path") or os.path.join(self.home(), "p")
         for content in contents:
             content_path = os.path.join(self.home(), content)
-            if content_path == packages_folder or content == "version.txt":
+            if content_path == packages_folder:
                 continue
             ConanOutput().debug(f"Removing {content_path}")
             if os.path.isdir(content_path):

conans/client/graph/compatibility.py

@@ -1,17 +1,47 @@
 import os
 from collections import OrderedDict
 
+from conan.api.output import ConanOutput
 from conan.internal.cache.home_paths import HomePaths
 from conans.client.graph.compute_pid import run_validate_package_id
 from conans.client.loader import load_python_file
 from conan.internal.errors import conanfile_exception_formatter, scoped_traceback
 from conan.errors import ConanException
+from conans.client.migrations import remove_if_guarded
 
 # TODO: Define other compatibility besides applications
 _default_compat = """\
 # This file was generated by Conan. Remove this comment if you edit this file or Conan
 # will destroy your changes.
-from cppstd_compat import cppstd_compat
+
+from conan.tools.build import supported_cppstd, supported_cstd
+from conan.errors import ConanException
+
+
+def cppstd_compat(conanfile):
+    # It will try to find packages with all the cppstd versions
+    extension_properties = getattr(conanfile, "extension_properties", {})
+    compiler = conanfile.settings.get_safe("compiler")
+    compiler_version = conanfile.settings.get_safe("compiler.version")
+    cppstd = conanfile.settings.get_safe("compiler.cppstd")
+    if not compiler or not compiler_version:
+        return []
+    factors = []  # List of list, each sublist is a potential combination
+    if cppstd is not None and extension_properties.get("compatibility_cppstd") is not False:
+        cppstd_possible_values = supported_cppstd(conanfile)
+        if cppstd_possible_values is None:
+            conanfile.output.warning(f'No cppstd compatibility defined for compiler "{compiler}"')
+        else: # The current cppst must be included in case there is other factor
+            factors.append([{"compiler.cppstd": v} for v in cppstd_possible_values])
+
+    cstd = conanfile.settings.get_safe("compiler.cstd")
+    if cstd is not None and extension_properties.get("compatibility_cstd") is not False:
+        cstd_possible_values = supported_cstd(conanfile)
+        if cstd_possible_values is None:
+            conanfile.output.warning(f'No cstd compatibility defined for compiler "{compiler}"')
+        else:
+            factors.append([{"compiler.cstd": v} for v in cstd_possible_values if v != cstd])
+    return factors
 
 
 def compatibility(conanfile):
@@ -51,48 +81,16 @@ def _factors_combinations(factors):
     return combinations
 """
 
-
-_default_cppstd_compat = """\
-# This file was generated by Conan. Remove this comment if you edit this file or Conan
-# will destroy your changes.
-from conan.tools.build import supported_cppstd, supported_cstd
-from conan.errors import ConanException
-
-
-def cppstd_compat(conanfile):
-    # It will try to find packages with all the cppstd versions
-    extension_properties = getattr(conanfile, "extension_properties", {})
-    compiler = conanfile.settings.get_safe("compiler")
-    compiler_version = conanfile.settings.get_safe("compiler.version")
-    cppstd = conanfile.settings.get_safe("compiler.cppstd")
-    if not compiler or not compiler_version:
-        return []
-    factors = []  # List of list, each sublist is a potential combination
-    if cppstd is not None and extension_properties.get("compatibility_cppstd") is not False:
-        cppstd_possible_values = supported_cppstd(conanfile)
-        if cppstd_possible_values is None:
-            conanfile.output.warning(f'No cppstd compatibility defined for compiler "{compiler}"')
-        else: # The current cppst must be included in case there is other factor
-            factors.append([{"compiler.cppstd": v} for v in cppstd_possible_values])
-
-    cstd = conanfile.settings.get_safe("compiler.cstd")
-    if cstd is not None and extension_properties.get("compatibility_cstd") is not False:
-        cstd_possible_values = supported_cstd(conanfile)
-        if cstd_possible_values is None:
-            conanfile.output.warning(f'No cstd compatibility defined for compiler "{compiler}"')
-        else:
-            factors.append([{"compiler.cstd": v} for v in cstd_possible_values if v != cstd])
-    return factors
-"""
-
-
 def migrate_compatibility_files(cache_folder):
     from conans.client.migrations import update_file
     compatible_folder = HomePaths(cache_folder).compatibility_plugin_path
     compatibility_file = os.path.join(compatible_folder, "compatibility.py")
     cppstd_compat_file = os.path.join(compatible_folder, "cppstd_compat.py")
     update_file(compatibility_file, _default_compat)
-    update_file(cppstd_compat_file, _default_cppstd_compat)
+    if not remove_if_guarded(cppstd_compat_file):
+        ConanOutput().warning('The "cppstd_compat.py" file is deprecated. Its contents have been moved '
+                              'to the "compatibility.py" file. Please remove it from your project, '
+                              'carrying over any modifications to the new location.')
 
 
 class BinaryCompatibility:

conans/client/migrations.py

@@ -6,7 +6,7 @@
 from conan.internal.default_settings import migrate_settings_file
 from conans.migrations import Migrator
 from conans.util.dates import timestamp_now
-from conans.util.files import load, save
+from conans.util.files import load, save, remove
 
 CONAN_GENERATED_COMMENT = "This file was generated by Conan"
 
@@ -33,6 +33,28 @@ def update_file(file_path, new_content):
             save(file_path, new_content)
             out.success(f"Migration: Successfully updated {file_name}")
 
+def remove_if_guarded(file_path):
+    """
+    Remove the file if it contains the ``CONAN_GENERATED_COMMENT``.
+
+    :param file_path: ``str`` path to the file.
+    """
+    out = ConanOutput()
+    file_name = os.path.basename(file_path)
+
+    if not os.path.exists(file_path):
+        return True
+
+    content = load(file_path)
+
+    first_line = content.lstrip().split("\n", 1)[0]
+
+    if CONAN_GENERATED_COMMENT in first_line:
+        remove(file_path)
+        out.success(f"Migration: Successfully removed {file_name}")
+        return True
+    return False
+
 
 class ClientMigrator(Migrator):
 

test/integration/command/config_test.py

@@ -232,7 +232,8 @@ def test_config_clean(storage_path):
     assert "bar" not in tc.out
     tc.run("config show core.upload:retry")
     assert "7" not in tc.out
-    assert not os.path.exists(os.path.join(tc.cache_folder, "extensions"))
+    assert os.path.exists(os.path.join(tc.cache_folder, "extensions"))
+    assert not os.path.exists(os.path.join(tc.cache_folder, "extensions", "compatibility", "mycomp.py"))
     assert os.path.exists(absolut_storage_path)
 
 

test/integration/test_migrations.py

@@ -151,3 +151,29 @@ def test_back_default_compatibility_migration():
     with patch('conan.api.conan_api.ClientMigrator', new=lambda *args, **kwargs: migrator):
         t.run("-v")  # Fire the backward migration
         assert f"WARN: Downgrading cache from Conan {conan_version} to 2.3.2" in t.out
+
+def test_migration_cppstd_compat_different_file():
+    t = TestClient()
+    t.run("-v")
+    assert 'WARN: The "cppstd_compat.py" file is deprecated' not in t.out
+
+    version_txt_file_path = os.path.join(t.cache_folder, "version.txt")
+    save(version_txt_file_path, "2.11")
+
+    cppstd_compat_file = os.path.join(t.cache_folder, "extensions", "plugins", "compatibility", "cppstd_compat.py")
+    save(cppstd_compat_file, "custom file content")
+
+    t.run("-v")
+    assert 'WARN: The "cppstd_compat.py" file is deprecated' in t.out
+    # Exists because it was not the default one
+    assert os.path.exists(cppstd_compat_file)
+
+    save(version_txt_file_path, "2.11")
+    cppstd_compat_file = os.path.join(t.cache_folder, "extensions", "plugins", "compatibility",
+                                      "cppstd_compat.py")
+    save(cppstd_compat_file, "# This file was generated by Conan. Remove this comment if you edit this file or Conan")
+
+    t.run("-v")
+    assert 'Migration: Successfully removed cppstd_compat.py' in t.out
+    # Removed because it was the default
+    assert not os.path.exists(cppstd_compat_file)