Make rebase_path("//foo", "//foo") resolve to "." (not "../foo")

tools/gn/function_rebase_path.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include "tools/gn/build_settings.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
@@ skipping 80 matching lines @@
 
   result = Value(function, Value::STRING);
   if (looks_like_dir) {
     result.string_value() = RebasePath(
         from_dir.ResolveRelativeDir(value, err,
             scope->settings()->build_settings()->root_path_utf8()).value(),
         to_dir,
         scope->settings()->build_settings()->root_path_utf8());
     MakeSlashEndingMatchInput(string_value, &result.string_value());
   } else {
-    result.string_value() = RebasePath(
+    SourceFile resolved_file =
         from_dir.ResolveRelativeFile(value, err,
-            scope->settings()->build_settings()->root_path_utf8()).value(),
-        to_dir,
-        scope->settings()->build_settings()->root_path_utf8());
+            scope->settings()->build_settings()->root_path_utf8());
     if (err->has_error())
       return Value();
+    // Special case:
+    //   rebase_path("//foo", "//bar") ==> "../foo"
+    //   rebase_path("//foo", "//foo") ==> "." and not "../foo"
+    if (resolved_file.value() ==
+        to_dir.value().substr(0, to_dir.value().size() - 1)) {
+      result.string_value() = ".";
+    } else {
+      result.string_value() = RebasePath(
+          resolved_file.value(),
+          to_dir,
+          scope->settings()->build_settings()->root_path_utf8());
+    }
   }
 
   return result;
 }
 
 }  // namespace
 
 const char kRebasePath[] = "rebase_path";
 const char kRebasePath_HelpShort[] =
     "rebase_path: Rebase a file or directory to another location.";
@@ skipping 162 matching lines @@
     }
     return result;
   }
 
   *err = Err(function->function(),
              "rebase_path requires a list or a string.");
   return result;
 }
 
 }  // namespace functions