fs: make replace_suffix not expand file to absolute path, just manipulate the string

docs/markdown/Fs-module.md

@@ -73,7 +73,7 @@ fs.samefile(x, z)  # true
 The `replace_suffix` method is a *string manipulation* convenient for filename modifications.
 It allows changing the filename suffix like:
 
-## swap suffix
+#### swap suffix
 
 ```meson
 original = '/opt/foo.ini'

mesonbuild/modules/fs.py

@@ -114,7 +114,7 @@ class FSModule(ExtensionModule):
     def replace_suffix(self, state: 'ModuleState', args: typing.Sequence[str], kwargs: dict) -> ModuleReturnValue:
         if len(args) != 2:
             MesonException('method takes exactly two arguments.')
-        original = PurePath(state.source_root) / state.subdir / args[0]
+        original = PurePath(args[0])
         new = original.with_suffix(args[1])
         return ModuleReturnValue(str(new), [])
 

test cases/common/227 fs module/meson.build

@@ -25,19 +25,19 @@ assert(not fs.is_file('~'), 'expanduser not working')
 
 original = 'foo.txt'
 new = fs.replace_suffix(original, '.ini')
-assert(new.endswith('foo.ini') and not new.contains('.txt'), 'replace_suffix failed')
+assert(new == 'foo.ini', 'replace_suffix failed')
 
 original = 'foo'
 new = fs.replace_suffix(original, '.ini')
-assert(new.endswith('foo.ini'), 'replace_suffix did not add suffix to suffixless file')
+assert(new == 'foo.ini', 'replace_suffix did not add suffix to suffixless file')
 
 original = 'foo.dll.a'
 new = fs.replace_suffix(original, '.so')
-assert(new.endswith('foo.dll.so'), 'replace_suffix did not only modify last suffix')
+assert(new == 'foo.dll.so', 'replace_suffix did not only modify last suffix')
 
 original = 'foo.dll'
 new = fs.replace_suffix(original, '')
-assert(new.endswith('foo'), 'replace_suffix did not only delete last suffix')
+assert(new == 'foo',  'replace_suffix did not only delete last suffix')
 
 # `/` on windows is interpreted like `.drive` which in general may not be `c:/`
 # the files need not exist for fs.replace_suffix()