ISSUE-16731: "msvc" compatibility with "Visual Studio" is broken (#16732

)

In case cppstd is set in the Conan profile for "Visual Studio", it is badly
migrated to "msvc". This change solves: #16731

The change also takes care of to handle the case when the 'default' cppstd is
set, in this case, it will be erased from the compatible package as well.

conans/model/info.py

@@ -591,15 +591,28 @@ def msvc_compatible(self):
         version = compatible.settings.compiler.version
         runtime = compatible.settings.compiler.runtime
         runtime_type = compatible.settings.compiler.runtime_type
+        cppstd = compatible.settings.compiler.get_safe("cppstd")
 
         compatible.settings.compiler = "Visual Studio"
+
+        if cppstd is not None:
+            # Restore cppstd, as switching to 'Visual Studio' clears it
+            compatible.settings.compiler.cppstd = cppstd
+
         from conan.tools.microsoft.visual import msvc_version_to_vs_ide_version
         visual_version = msvc_version_to_vs_ide_version(version)
         compatible.settings.compiler.version = visual_version
         runtime = "MT" if runtime == "static" else "MD"
         if runtime_type == "Debug":
             runtime = "{}d".format(runtime)
         compatible.settings.compiler.runtime = runtime
+
+        # Some 'final adjustment'
+        # In case the cppstd is the 'default' for the compiler, it will actually be erased
+        default_cppstd = cppstd_default(compatible.settings)
+        if default_cppstd is not None and compatible.settings.compiler.get_safe("cppstd") == default_cppstd:
+            del compatible.settings.compiler.cppstd
+
         return compatible
 
     def apple_clang_compatible(self):

conans/test/integration/package_id/compatible_test.py

@@ -604,25 +604,45 @@ def package_id(self):
 def test_msvc_visual_incompatible():
     conanfile = GenConanfile().with_settings("os", "compiler", "build_type", "arch")
     client = TestClient()
-    profile = textwrap.dedent("""
+    # First we need to make sure to test that a 'non-default' cppstd is actually preserved
+    # and we can match that
+    profile1 = textwrap.dedent("""
         [settings]
         os=Windows
         compiler=msvc
         compiler.version=191
         compiler.runtime=dynamic
-        compiler.cppstd=14
+        compiler.cppstd=17
         build_type=Release
         arch=x86_64
         """)
     client.save({"conanfile.py": conanfile,
-                 "profile": profile})
+                 "profile1": profile1})
     client.run('create . pkg/0.1@ -s os=Windows -s compiler="Visual Studio" -s compiler.version=15 '
+               '-s compiler.cppstd=17 -s compiler.runtime=MD -s build_type=Release -s arch=x86_64')
+    client.run("install pkg/0.1@ -pr=profile1")
+    assert "Using compatible package" in client.out
+
+    # Now we need to test the 'default' cppstd case, in this case, this will be lost in the package id
+    profile2 = textwrap.dedent("""
+        [settings]
+        os=Windows
+        compiler=msvc
+        compiler.version=191
+        compiler.runtime=dynamic
+        compiler.cppstd=14
+        build_type=Release
+        arch=x86_64
+        """)
+    client.save({"profile2": profile2})
+    client.run('create . pkg/0.2@ -s os=Windows -s compiler="Visual Studio" -s compiler.version=15 '
                '-s compiler.runtime=MD -s build_type=Release -s arch=x86_64')
-    client.run("install pkg/0.1@ -pr=profile")
+    client.run("install pkg/0.2@ -pr=profile2")
     assert "Using compatible package" in client.out
+
     new_config = "core.package_id:msvc_visual_incompatible=1"
     save(client.cache.new_config_path, new_config)
-    client.run("install pkg/0.1@ -pr=profile", assert_error=True)
+    client.run("install pkg/0.1@ -pr=profile1", assert_error=True)
     assert "ERROR: Missing prebuilt package for 'pkg/0.1'" in client.out