install_subdir: Also copy dangling symlinks

Fixes https://github.com/mesonbuild/meson/issues/3914

mesonbuild/minstall.py

@@ -191,12 +191,16 @@ class Installer:
     def should_preserve_existing_file(self, from_file, to_file):
         if not self.options.only_changed:
             return False
+        # Always replace danging symlinks
+        if os.path.islink(from_file) and not os.path.isfile(from_file):
+            return False
         from_time = os.stat(from_file).st_mtime
         to_time = os.stat(to_file).st_mtime
         return from_time <= to_time
 
     def do_copyfile(self, from_file, to_file):
-        if not os.path.isfile(from_file):
+        outdir = os.path.split(to_file)[0]
+        if not os.path.isfile(from_file) and not os.path.islink(from_file):
             raise RuntimeError('Tried to install something that isn\'t a file:'
                                '{!r}'.format(from_file))
         # copyfile fails if the target file already exists, so remove it to
@@ -210,11 +214,13 @@ class Installer:
                 append_to_log(self.lf, '# Preserving old file %s\n' % to_file)
                 print('Preserving existing file %s.' % to_file)
                 return False
-            os.unlink(to_file)
-        outdir = os.path.split(to_file)[0]
+            os.remove(to_file)
         print('Installing %s to %s' % (from_file, outdir))
-        shutil.copyfile(from_file, to_file)
-        shutil.copystat(from_file, to_file)
+        if os.path.islink(from_file):
+            shutil.copy(from_file, outdir, follow_symlinks=False)
+        else:
+            shutil.copyfile(from_file, to_file)
+            shutil.copystat(from_file, to_file)
         selinux_updates.append(to_file)
         append_to_log(self.lf, to_file)
         return True
@@ -277,7 +283,7 @@ class Installer:
                 if os.path.isdir(abs_dst):
                     print('Tried to copy file %s but a directory of that name already exists.' % abs_dst)
                 if os.path.exists(abs_dst):
-                    os.unlink(abs_dst)
+                    os.remove(abs_dst)
                 parent_dir = os.path.dirname(abs_dst)
                 if not os.path.isdir(parent_dir):
                     os.mkdir(parent_dir)
@@ -438,7 +444,7 @@ class Installer:
                 try:
                     symlinkfilename = os.path.join(outdir, alias)
                     try:
-                        os.unlink(symlinkfilename)
+                        os.remove(symlinkfilename)
                     except FileNotFoundError:
                         pass
                     os.symlink(to, symlinkfilename)

run_unittests.py

@@ -3779,6 +3779,32 @@ endian = 'little'
             # Ensure that the otool output does not contain self.installdir
             self.assertNotRegex(out, self.installdir + '.*dylib ')
 
+    def test_install_subdir_symlinks(self):
+        '''
+        Test that installation of broken symlinks works fine.
+        https://github.com/mesonbuild/meson/issues/3914
+        '''
+        testdir = os.path.join(self.common_test_dir, '66 install subdir')
+        subdir = os.path.join(testdir, 'sub/sub1')
+        curdir = os.getcwd()
+        os.chdir(subdir)
+        # Can't distribute broken symlinks in the source tree because it breaks
+        # the creation of zipapps. Create it dynamically and run the test by
+        # hand.
+        src = '../../nonexistent.txt'
+        os.symlink(src, 'test.txt')
+        try:
+            self.init(testdir)
+            self.build()
+            self.install()
+            link = os.path.join(self.installdir, 'usr', 'share', 'sub1', 'test.txt')
+            self.assertTrue(os.path.islink(link), msg=link)
+            self.assertEqual(src, os.readlink(link))
+            self.assertFalse(os.path.isfile(link), msg=link)
+        finally:
+            os.remove(os.path.join(subdir, 'test.txt'))
+            os.chdir(curdir)
+
 
 class LinuxCrossArmTests(BasePlatformTests):
     '''