runfiles,C++: implement manifest-based runfiles

Implement a manifest-based Runfiles object, add
tests and test utils (MockFile).

Subsequent commits will add more feataures:
- creating list of envvars to pass to child
  processes
- automatic Runfiles creation based on argv[0] and
  the envvars of this process

See https://github.com/bazelbuild/bazel/issues/4460

Change-Id: I4376ede3ac00241688ff16a36ed596fb08f13a72
PiperOrigin-RevId: 187318502

1 files changed, 6 insertions, 2 deletions

diff --git a/src/tools/runfiles/runfiles.h b/src/tools/runfiles/runfiles.h
index c15dec39e0..821cc1aa6f 100644
--- a/src/tools/runfiles/runfiles.h
+++ b/src/tools/runfiles/runfiles.h
@@ -32,8 +32,12 @@ class Runfiles {
   //   Runfiles* Create(const string& argv0, string* error);
   // TODO(laszlocsomor): implement:
   //   vector<pair<string, string>> EnvVars();
-  // TODO(laszlocsomor): implement:
-  //   Runfiles* CreateManifestBased(const string& path, string* error);
+
+  // Returns a new manifest-based `Runfiles` instance.
+  // Returns nullptr on error. If `error` is provided, the method prints an
+  // error message into it.
+  static Runfiles* CreateManifestBased(const std::string& manifest_path,
+                                       std::string* error = nullptr);
 
   // Returns a new directory-based `Runfiles` instance.
   // Returns nullptr on error. If `error` is provided, the method prints an