build: Provide backward compatability for targets with path separators

When a target name includes a path separator, extract the basename and
assign that to the 'install_name' property. Then replace the path
separators with '_' to 'flatten' the name, avoiding incidental
creation of directories inside the build tree.

Projects which depend on this behavior can be converted to use
'install_name' directly, once they depend on a version of meson with
that feature.

Signed-off-by: Keith Packard <[email protected]>

mesonbuild/build.py

@@ -37,6 +37,7 @@
     get_filenames_templates_dict, substitute_values, has_path_sep,
     OptionKey, PerMachineDefaultable, OptionOverrideProxy,
     MesonBugException, EnvironmentVariables, pickle_load,
+    flatten_path,
 )
 from .compilers import (
     is_object, clink_langs, sort_clink, all_languages,
@@ -538,13 +539,9 @@ def __post_init__(self, overrides: T.Optional[T.Dict[OptionKey, str]]) -> None:
         else:
             ovr = {}
         self.options = OptionOverrideProxy(ovr, self.environment.coredata.options, self.subproject)
-        # XXX: this should happen in the interpreter
         if has_path_sep(self.name):
-            # Fix failing test 53 when this becomes an error.
-            mlog.warning(textwrap.dedent(f'''\
-                Target "{self.name}" has a path separator in its name.
-                This is not supported, it can cause unexpected failures and will become
-                a hard error in the future.'''))
+            self.install_name = os.path.basename(self.name)
+            self.name = flatten_path(self.name)
 
     # dataclass comparators?
     def __lt__(self, other: object) -> bool:

mesonbuild/utils/universal.py

@@ -112,6 +112,7 @@ class _VerPickleLoadable(Protocol):
     'expand_arguments',
     'extract_as_list',
     'first',
+    'flatten_path',
     'generate_list',
     'get_compiler_for_source',
     'get_filenames_templates_dict',
@@ -1091,6 +1092,16 @@ def has_path_sep(name: str, sep: str = '/\\') -> bool:
     return False
 
 
+def flatten_path(name: str, sep: str = '/\\', replace: str = '_') -> str:
+    'Replaces any specified @sep path separators in @name with @replace'
+    result = ''
+    for char in name:
+        if char in sep:
+            char = replace
+        result = result + char
+    return result
+
+
 if is_windows():
     # shlex.split is not suitable for splitting command line on Window (https://bugs.python.org/issue1724822);
     # shlex.quote is similarly problematic. Below are "proper" implementations of these functions according to