Fix cppstd_compat migration for 2.12 (#17647)

* Remove cppstdcompat if guarded, warn otherwise, move to main compatibility file

* Conan config clean is better if it regenerates default files

* Add migration test for compatibility

* Fix conan config clean test

* Remove initial try

* Franchu was right

* Move to its own RP

* wip

* fix test

* fixed tests

---------

Co-authored-by: memsharded <[email protected]>

conans/client/graph/compatibility.py

@@ -1,17 +1,49 @@
 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 CONAN_GENERATED_COMMENT
 
 # TODO: Define other compatibility besides applications
+from conans.util.files import load, save
+
 _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):
@@ -52,47 +84,24 @@ def _factors_combinations(factors):
 """
 
 
-_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)
+
+    def _should_migrate_file(file_path):
+        if not os.path.exists(file_path):
+            return True
+        content = load(file_path)
+        first_line = content.lstrip().split("\n", 1)[0]
+        return CONAN_GENERATED_COMMENT in first_line
+
+    if _should_migrate_file(compatibility_file) and _should_migrate_file(cppstd_compat_file):
+        if os.path.exists(compatibility_file) and load(compatibility_file) != _default_compat:
+            ConanOutput().success("Migration: Successfully updated compatibility.py}")
+        save(compatibility_file, _default_compat)
+        if os.path.exists(cppstd_compat_file):
+            os.remove(cppstd_compat_file)
 
 
 class BinaryCompatibility:

test/integration/test_migrations.py

@@ -31,8 +31,7 @@ def _drop_lru_column(db_folder):
 
 @pytest.mark.parametrize(["plugin_path", "string_replace", "new_string"],
                          [("profile.py", "msvc", "EME_ESE_VC"),
-                          ("compatibility/compatibility.py", "conanfile", "conian_file"),
-                          ("compatibility/cppstd_compat.py", "conanfile", "conian_file")])
+                          ("compatibility/compatibility.py", "conanfile", "conian_file")])
 def test_migration_profile_checker_plugin(plugin_path, string_replace, new_string):
     t = TestClient()
     # Any command that checks the package cache generates the DB
@@ -151,3 +150,44 @@ 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
+
+
+class TestMigrationCppstdCompat:
+    def test_migration(self):
+        t = TestClient()
+        t.run("-v")
+        cppstd_compat_path = "extensions/plugins/compatibility/cppstd_compat.py"
+        compatibility_path = "extensions/plugins/compatibility/compatibility.py"
+
+        # both files exist and not modified
+        t.save_home({"version.txt": "2.11"})
+        t.run("-v")
+        assert "def cppstd_compat(conanfile)" in t.load_home(compatibility_path)
+        assert not os.path.exists(os.path.join(t.cache_folder, cppstd_compat_path))
+
+    def test_cppstd_modified(self):
+        t = TestClient()
+        t.run("-v")
+        cppstd_compat_path = "extensions/plugins/compatibility/cppstd_compat.py"
+        compatibility_path = "extensions/plugins/compatibility/compatibility.py"
+        # cppstd_compat modified
+        t.save_home({"version.txt": "2.11",
+                     compatibility_path: "# This file was generated by Conan",
+                     cppstd_compat_path: "custom file content"})
+        t.run("-v")
+        assert t.load_home(cppstd_compat_path) == "custom file content"
+        # compatibility not migrated, keeps the old content
+        assert "def cppstd_compat(conanfile)" not in t.load_home(compatibility_path)
+
+    def test_compatibility_modified(self):
+        t = TestClient()
+        t.run("-v")
+        cppstd_compat_path = "extensions/plugins/compatibility/cppstd_compat.py"
+        compatibility_path = "extensions/plugins/compatibility/compatibility.py"
+        t.save_home({"version.txt": "2.11",
+                     cppstd_compat_path: "# This file was generated by Conan POTATO",
+                     compatibility_path: "Modified file"})
+        t.run("-v")
+        assert t.load_home(compatibility_path) == "Modified file"
+        # not Removed because compatibility was modified
+        assert "POTATO" in t.load_home(cppstd_compat_path)