Reference written files relatively when possible.

tools/gn/filesystem_utils_unittest.cc

Index: tools/gn/filesystem_utils_unittest.cc
diff --git a/tools/gn/filesystem_utils_unittest.cc b/tools/gn/filesystem_utils_unittest.cc
index 14bc9515307e3767a108ff2f358a7789b68eb7a5..44b0fa5895331a9c0c612cfa6eda7197a93d8ba1 100644
--- a/tools/gn/filesystem_utils_unittest.cc
+++ b/tools/gn/filesystem_utils_unittest.cc
@@ -119,6 +119,51 @@ TEST(FilesystemUtils, EnsureStringIsInOutputDir) {
   EXPECT_TRUE(err.has_error());
 }
 
+TEST(FilesystemUtils, ComputeStringInOutputDir) {
+  SourceDir out_d("//out/Debug/");
+  SourceFile foo("//foo");
+  SourceFile debugit("//out/Debugit");
+  SourceFile out_less("//out/Debug");
+
+  // Some outside.
+  Err err;
+  EXPECT_EQ("", ComputeStringInOutputDir(out_d, foo, &err));
+  EXPECT_TRUE(err.has_error());
+
+  err = Err();
+  EXPECT_EQ("", ComputeStringInOutputDir(out_d, debugit, &err));
+  EXPECT_TRUE(err.has_error());
+
+  // Some inside.
+  err = Err();
+  EXPECT_EQ("", ComputeStringInOutputDir(out_d, out_less, &err));
+  EXPECT_TRUE(err.has_error());
+
+  err = Err();
+  const char * const r_a = "a";
+  SourceFile a("//out/Debug/a");
+  EXPECT_EQ(r_a, ComputeStringInOutputDir(out_d, a, &err));
+  EXPECT_FALSE(err.has_error());
+
+  err = Err();
+  const char * const r_ofoo = "foo";
+  SourceFile ofoo("//out/Debug/foo");
+  EXPECT_EQ(r_ofoo, ComputeStringInOutputDir(out_d, ofoo, &err));
+  EXPECT_FALSE(err.has_error());
+
+  err = Err();
+  const char * const r_olong = "super-cal/bong/pas";
+  SourceFile olong("//out/Debug/super-cal/bong/pas");
+  EXPECT_EQ(r_olong, ComputeStringInOutputDir(out_d, olong, &err));
+  EXPECT_FALSE(err.has_error());
+
+  // Pattern but no template expansions are allowed.
+  SourceFile wrong("//{{source_gen_dir}}");
+  EXPECT_EQ("", ComputeStringInOutputDir(out_d, wrong, &err));
+  EXPECT_TRUE(err.has_error());
+
+}
+
 TEST(FilesystemUtils, IsPathAbsolute) {
   EXPECT_TRUE(IsPathAbsolute("/foo/bar"));
   EXPECT_TRUE(IsPathAbsolute("/"));