fs: add expanduser method

this should help users specify leading `~` in various Meson options and variables
without refactoring lots of places inside Meson itself.

docs/markdown/Fs-module.md

@@ -37,7 +37,7 @@ by the string is a symbolic link.
 
 ### is_absolute
 
-Return a boolean indicating if the path string specified is absolute for this computer, WITHOUT expanding `~`.
+Return a boolean indicating if the path string specified is absolute, WITHOUT expanding `~`.
 
 Examples:
 
@@ -96,7 +96,19 @@ fs.is_samepath(p, s)  # false
 
 ## Filename modification
 
-The files need not actually exist yet for these methods, as they are just string manipulation.
+The files need not actually exist yet for these path string manipulation methods.
+
+### expanduser
+
+A path string with a leading `~` is expanded to the user home directory
+
+Examples:
+
+```meson
+fs.expanduser('~')  # home directory
+
+fs.expanduser('~/foo')  # <homedir>/foo
+```
 
 ### as_posix
 

mesonbuild/modules/fs.py

@@ -14,7 +14,7 @@
 
 import typing as T
 import hashlib
-from pathlib import Path, PurePath
+from pathlib import Path, PurePath, PureWindowsPath
 
 from .. import mlog
 from . import ExtensionModule
@@ -60,6 +60,13 @@ class FSModule(ExtensionModule):
             val = str(val)
         return ModuleReturnValue(val, [])
 
+    @stringArgs
+    @noKwargs
+    def expanduser(self, state: 'ModuleState', args: T.Sequence[str], kwargs: dict) -> ModuleReturnValue:
+        if len(args) != 1:
+            raise MesonException('fs.expanduser takes exactly one argument.')
+        return ModuleReturnValue(str(Path(args[0]).expanduser()), [])
+
     @stringArgs
     @noKwargs
     def is_absolute(self, state: 'ModuleState', args: T.Sequence[str], kwargs: dict) -> ModuleReturnValue:

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

@@ -30,8 +30,12 @@ assert(fs.is_dir('subprojects'), 'Dir not detected correctly.')
 assert(not fs.is_dir('meson.build'), 'File detected as a dir.')
 assert(not fs.is_dir('nonexisting'), 'Bad path detected as a dir.')
 
-assert(fs.is_dir('~'), 'expanduser not working')
-assert(not fs.is_file('~'), 'expanduser not working')
+assert(fs.is_dir('~'), 'home directory not detected')
+assert(not fs.is_file('~'), 'home directory detected as file')
+
+# -- expanduser
+assert(fs.expanduser('~') != '~','expanduser failed')
+assert(fs.expanduser('~/foo').endswith('foo'), 'expanduser with tail failed')
 
 # -- as_posix
 assert(fs.as_posix('/') == '/', 'as_posix idempotent')