expand tilde when looking up libraries -Dfoo=~/mylib

It is often desirable to use ~ for home directory in -D compilation args.

Why the transform to pathlib.Path and back to str? Because this is one of many
places where the list(map(str,..))) will be eliminated upon Python 3.6 being
minimum Meson Python requirement.

mesonbuild/interpreter.py

@@ -33,6 +33,7 @@ from .interpreterbase import ObjectHolder
 from .modules import ModuleReturnValue
 from .cmake import CMakeInterpreter
 
+from pathlib import Path
 import os, shutil, uuid
 import re, shlex
 import subprocess
@@ -1543,9 +1544,12 @@ class CompilerHolder(InterpreterObject):
                 return self.notfound_library(libname)
 
         search_dirs = mesonlib.stringlistify(kwargs.get('dirs', []))
-        for i in search_dirs:
-            if not os.path.isabs(i):
-                raise InvalidCode('Search directory %s is not an absolute path.' % i)
+        search_dirs = [Path(d).expanduser() for d in search_dirs]
+        for d in search_dirs:
+            if not d.is_absolute():
+                raise InvalidCode('Search directory {} is not an absolute path.'.format(d))
+        search_dirs = list(map(str, search_dirs))
+
         libtype = mesonlib.LibType.PREFER_SHARED
         if 'static' in kwargs:
             if not isinstance(kwargs['static'], bool):