Repository: bazelbuild/bazel
Issue: Implement "Locating runfiles with Bzlmod" proposal
Labels: type: feature request
P2
team-ExternalDeps
area-Bzlmod

The ["Locating runfiles with Bzlmod" proposal](https://github.com/bazelbuild/proposals/blob/main/designs/2022-07-21-locating-runfiles-with-bzlmod.md) consists of the following individual steps:

* [x] ~Add the `RunfilesLibraryInfo` provider (#16125)~
* [x] Collect repository names and mappings of the transitive closure of a target (#16278)
* [x] Emit a repository mapping manifest for every executable (#16321 and https://github.com/bazelbuild/bazel/pull/16652)
* [x] Revert `RunfilesLibraryInfo`
* [x] Expose the current repository name in rules
  * [x] Bash (#16693)
  * [x] C++ (#16216)
  * [x] Java (#16534)
  * [x] Python (#16341)
* [x] Parse and use the repository mapping manifest in runfiles libraries (https://github.com/bazelbuild/bazel/issues/15029)
  * [x] Bash (#16693)
  * [x] C++ (#16623 and https://github.com/bazelbuild/bazel/pull/16701)
  * [x] Java (#16549)
  * [X] ~Python~ has been updated in rules_python
* [x] Use the Java runfiles library to make Stardoc work with repository mappings (https://github.com/bazelbuild/bazel/issues/14140)

Status of runfiles libraries in third-party rulesets:

* [x] rules_go (https://github.com/bazelbuild/rules_go/pull/3347)
* [ ] [rules_rust](https://github.com/bazelbuild/rules_rust/blob/main/tools/runfiles/runfiles.rs) (???)
* [ ] [rules_haskell](https://github.com/tweag/rules_haskell/blob/master/tools/runfiles/README.md) (???)

Issue comments:
@Wyverald Could you assign me and add the appropriate labels?
~~@comius Do you expect `java_binary` to be starlarkified in time for Bazel 6? That would simplify the changes to the Java rules.~~ Most likely no longer necessary, as the changes will apply to `buildjar` itself.
@Wyverald Oops, I missed the use of `Closes ...` in the PR description - we should use `Work towards ...` instead. Could you reopen? For some I lack the permission to do so.
It's the "To fix #NNN" line... GitHub trying to be clever here
The most likely future seems to be that we'll standardize on Python imports _not_ containing the repository name, in which case bzlmod is a no-op.

It's not an optimal solution because it requires an entry in `$PYTHONPATH` for each repository in the transitive closure of the Python binary, but it's the status quo and I'd much prefer thinking up a solution to that (e.g. binary-specific symlink trees that do not look like runfiles trees, dunno) than to standardize on having the repository names in imports because the concept of "repository" is specific to Bazel.

Put differently: the only way for bzlmod to cause trouble for Python is if we decide to require repository names in imports, which seems to be unlikely and it looks like the decision on that will take a while and I prefer not blocking either Bazel 6.0 or the removal of bzlmod from the experimental domain to avoid an unlikely failure mode. And should that happen, we can always paper over it with some sort of import hook.

/cc @rickeylev 
@oquenchil I'm thinking about whether we should use a macro to pass `BAZEL_CURRENT_REPOSITORY` to the `Rlocation` function automatically (e.g. do `#define Rlocation(path) RlocationReal(path, BAZEL_CURRENT_REPOSITORY)`). Do you think that would be too intrusive/magical?
Would users have to write that line or is it part of a file that is automatically generated?

I don't mind adding whatever will make it easier but if it gets too magical it should maybe be wrapped so that the details aren't visible to the user unless they want to look.
> Would users have to write that line or is it part of a file that is automatically generated?
> 
> I don't mind adding whatever will make it easier but if it gets too magical it should maybe be wrapped so that the details aren't visible to the user unless they want to look.

@oquenchil I would want to make that magic part of the runfiles library header so that users don't have to write it themselves.

What I am worried about is having an `Rlocation` macro mess with people's existing codebase since there doesn't seem to be a way to put it in a namespace or restrict it to member functions only.
Aren't we in control of the name of the macro? Can we rename it to something that would be very unlikely to clash with anything?
> Aren't we in control of the name of the macro? Can we rename it to something that would be very unlikely to clash with anything?

We can call it something else, we just won't be able to have existing C++ codebases use the new repo mapping-aware lookup automatically if we do so. But of course having to replace all `runfiles::create()` calls with something else won't be too bad.
If the macro name is Rlocation and that may start clashing with people's code in C++ files then I think it would be prudent to rename it if we decide to go with the macro.

I guess the call to make here is how much of a breaking change this is compared to the benefit of passing BAZEL_CURRENT_REPOSITORY automatically for users. I would say that the benefit is not too great but as far as I understood the use of Bazel runfiles in C++ code wasn't too wide-spread either?

>  But of course having to replace all runfiles::create() calls with something else won't be too bad.

How do you know? Is it based on search results from GH? If a release note would be enough for it not to be too disruptive then let's rename it.
I have experimented a bit more with APIs while working on the corresponding change for Java (https://github.com/bazelbuild/bazel/pull/16549).

What I now like more than the macro approach is to have users (optionally) pass in a canonical repository name when creating the `Runfiles` instance and default to that repo in `Rlocation` calls, while providing ways to override the default with an overload of `Rlocation` that accepts a repository name as a second parameter. In this way, users only have to pass in `BAZEL_CURRENT_REPOSITORY` only once in the common case, which should render a macro unnecessary.
Update: All changes relevant for Bazel 6.0.0 are now in review.
This is mostly done now, with only the bugfix https://github.com/bazelbuild/bazel/pull/16755 and a number of cherry-picks to 6.0.0 missing.
@Wyverald You can remove this from the "6.0.0 nice to have" milestone as the only remaining issue is not tied to a Bazel release (Stardoc).
Downgrading because the most important points have been addressed; the only outstanding issue is Stardoc, which is undergoing a rewrite currently by @tetromino.

Pull request review comments:

Patch that resolved the issue:
diff --git a/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm b/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
index 096a6eac0aea0d..f5ac7d1c84abcf 100644
--- a/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
+++ b/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
@@ -262,15 +262,15 @@
     </p>
     <p>
       Output files are staged similarly, but are also prefixed with the subpath
-      <code>bazel-out/cpu-compilation_mode/bin</code> (or for certain outputs:
-      <code>bazel-out/cpu-compilation_mode/genfiles</code>, or for the outputs
-      of host tools: <code>bazel-out/host/bin</code>). In the above example,
-      <code>//testapp:app</code> is a host tool because it appears in
+      <code>bazel-out/cpu-compilation_mode/bin</code> (or for the outputs of
+      tools: <code>bazel-out/cpu-opt-exec-hash/bin</code>). In the above example,
+      <code>//testapp:app</code> is a tool because it appears in
       <code>show_app_output</code>'s <code><a
       href="$expander.expandRef("genrule.tools")">tools</a></code> attribute.
       So its output file <code>app</code> is written to
-      <code>bazel-myproject/bazel-out/host/bin/testapp/app</code>. The exec path
-      is thus <code>bazel-out/host/bin/testapp/app</code>. This extra prefix
+      <code>bazel-myproject/bazel-out/cpu-opt-exec-hash/bin/testapp/app</code>.
+      The exec path is thus <code>
+      bazel-out/cpu-opt-exec-hash/bin/testapp/app</code>. This extra prefix
       makes it possible to build the same target for, say, two different CPUs in
       the same build without the results clobbering each other.
     </p>
@@ -284,15 +284,57 @@
 
   <li>
     <p>
-      <code>rootpath</code>: Denotes the runfiles path that a built binary can
-      use to find its dependencies at runtime.
-    </p>
+      <code>rootpath</code>: Denotes the path that a built binary can use to
+      find a dependency at runtime relative to the subdirectory of its runfiles
+      directory corresponding to the main repository.
+      <strong>Note:</strong> This only works if <a
+            href="/reference/command-line-reference#flag--enable_runfiles">
+      <code>--enable_runfiles</code></a> is enabled, which is not the case on
+      Windows by default. Use <code>rlocationpath</code> instead for
+      cross-platform support.
     <p>
-      This is the same as <code>execpath</code> but strips the output prefixes
-      described above. In the above example this means both
+      This is similar to <code>execpath</code> but strips the configuration
+      prefixes described above. In the example from above this means both
       <code>empty.source</code> and <code>app</code> use pure workspace-relative
       paths: <code>testapp/empty.source</code> and <code>testapp/app</code>.
     </p>
+    <p>
+      The <code>rootpath</code> of a file in an external repository
+      <code>repo</code> will start with <code>../repo/</code>, followed by the
+      repository-relative path.
+    </p>
+    <p>
+      This has the same "one output only" requirements as <code>execpath</code>.
+    </p>
+  </li>
+
+  <li>
+    <p>
+      <code>rlocationpath</code>: The path a built binary can pass to the <code>
+      Rlocation</code> function of a runfiles library to find a dependency at
+      runtime, either in the runfiles directory (if available) or using the
+      runfiles manifest.
+    </p>
+    <p>
+      This is similar to <code>rootpath</code> in that it does not contain
+      configuration prefixes, but differs in that it always starts with the
+      name of the repository. In the example from above this means that <code>
+      empty.source</code> and <code>app</code> result in the following
+      paths: <code>myproject/testapp/empty.source</code> and <code>
+      myproject/testapp/app</code>.
+    </p>
+    <p>
+      The <code>rlocationpath</code> of a file in an external repository
+      <code>repo</code> will start with <code>repo/</code>, followed by the
+      repository-relative path.
+    </p>
+    <p>
+      Passing this path to a binary and resolving it to a file system path using
+      the runfiles libraries is the preferred approach to find dependencies at
+      runtime. Compared to <code>rootpath</code>, it has the advantage that it
+      works on all platforms and even if the runfiles directory is not
+      available.
+    </p>
     <p>
       This has the same "one output only" requirements as <code>execpath</code>.
     </p>
@@ -303,24 +345,25 @@
     <code>rootpath</code>, depending on the attribute being expanded. This is
     legacy pre-Starlark behavior and not recommended unless you really know what
     it does for a particular rule. See <a
-    href="https://github.com/bazelbuild/bazel/issues/2475#issuecomment-339318016">#2475</a>
+          href="https://github.com/bazelbuild/bazel/issues/2475#issuecomment-339318016">#2475</a>
     for details.
   </li>
 </ul>
 
 <p>
-  <code>execpaths</code>, <code>rootpaths</code>, and <code>locations</code> are
-  the plural variations of <code>execpath</code>, <code>rootpath</code>, and
-  <code>location</code>, respectively. They support labels producing multiple
-  outputs, in which case each output is listed separated by a space. Zero-output
-  rules and malformed labels produce build errors.
+  <code>execpaths</code>, <code>rootpaths</code>, <code>rlocationpaths</code>,
+  and <code>locations</code> are the plural variations of <code>execpath</code>,
+  <code>rootpath</code>, <code>rlocationpaths</code>, and<code>location</code>,
+  respectively. They support labels producing multiple outputs, in which case
+  each output is listed separated by a space. Zero-output rules and malformed
+  labels produce build errors.
 </p>
 
 <p>
   All referenced labels must appear in the consuming target's <code>srcs</code>,
   output files, or <code>deps</code>. Otherwise the build fails. C++ targets can
   also reference labels in <code><a
-  href="$expander.expandRef("cc_binary.data")">data</a></code>.
+        href="$expander.expandRef("cc_binary.data")">data</a></code>.
 </p>
 
 <p>
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/LocationExpander.java b/src/main/java/com/google/devtools/build/lib/analysis/LocationExpander.java
index d82d3de89a0f7d..ddcf5510ac174d 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/LocationExpander.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/LocationExpander.java
@@ -17,6 +17,7 @@
 import static java.util.stream.Collectors.joining;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
 import com.google.common.base.Supplier;
 import com.google.common.base.Suppliers;
 import com.google.common.collect.ImmutableCollection;
@@ -26,7 +27,9 @@
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.analysis.LocationExpander.LocationFunction.PathType;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.RepositoryMapping;
 import com.google.devtools.build.lib.packages.BuildType;
@@ -63,34 +66,35 @@ public final class LocationExpander {
   private static final boolean EXACTLY_ONE = false;
   private static final boolean ALLOW_MULTIPLE = true;
 
-  private static final boolean USE_LOCATION_PATHS = false;
-  private static final boolean USE_EXEC_PATHS = true;
-
   private final RuleErrorConsumer ruleErrorConsumer;
   private final ImmutableMap<String, LocationFunction> functions;
   private final RepositoryMapping repositoryMapping;
+  private final String workspaceRunfilesDirectory;
 
   @VisibleForTesting
   LocationExpander(
       RuleErrorConsumer ruleErrorConsumer,
       Map<String, LocationFunction> functions,
-      RepositoryMapping repositoryMapping) {
+      RepositoryMapping repositoryMapping,
+      String workspaceRunfilesDirectory) {
     this.ruleErrorConsumer = ruleErrorConsumer;
     this.functions = ImmutableMap.copyOf(functions);
     this.repositoryMapping = repositoryMapping;
+    this.workspaceRunfilesDirectory = workspaceRunfilesDirectory;
   }
 
   private LocationExpander(
-      RuleErrorConsumer ruleErrorConsumer,
+      RuleContext ruleContext,
       Label root,
       Supplier<Map<Label, Collection<Artifact>>> locationMap,
       boolean execPaths,
       boolean legacyExternalRunfiles,
       RepositoryMapping repositoryMapping) {
     this(
-        ruleErrorConsumer,
+        ruleContext,
         allLocationFunctions(root, locationMap, execPaths, legacyExternalRunfiles),
-        repositoryMapping);
+        repositoryMapping,
+        ruleContext.getWorkspaceName());
   }
 
   /**
@@ -204,7 +208,10 @@ private String expand(String value, ErrorReporter reporter) {
       // (2) Call appropriate function to obtain string replacement.
       String functionValue = value.substring(nextWhitespace + 1, end).trim();
       try {
-        String replacement = functions.get(fname).apply(functionValue, repositoryMapping);
+        String replacement =
+            functions
+                .get(fname)
+                .apply(functionValue, repositoryMapping, workspaceRunfilesDirectory);
         result.append(replacement);
       } catch (IllegalStateException ise) {
         reporter.report(ise.getMessage());
@@ -232,23 +239,29 @@ public String expandAttribute(String attrName, String attrValue) {
 
   @VisibleForTesting
   static final class LocationFunction {
+    enum PathType {
+      LOCATION,
+      EXEC,
+      RLOCATION,
+    }
+
     private static final int MAX_PATHS_SHOWN = 5;
 
     private final Label root;
     private final Supplier<Map<Label, Collection<Artifact>>> locationMapSupplier;
-    private final boolean execPaths;
+    private final PathType pathType;
     private final boolean legacyExternalRunfiles;
     private final boolean multiple;
 
     LocationFunction(
         Label root,
         Supplier<Map<Label, Collection<Artifact>>> locationMapSupplier,
-        boolean execPaths,
+        PathType pathType,
         boolean legacyExternalRunfiles,
         boolean multiple) {
       this.root = root;
       this.locationMapSupplier = locationMapSupplier;
-      this.execPaths = execPaths;
+      this.pathType = Preconditions.checkNotNull(pathType);
       this.legacyExternalRunfiles = legacyExternalRunfiles;
       this.multiple = multiple;
     }
@@ -259,10 +272,13 @@ static final class LocationFunction {
      * using the {@code repositoryMapping}.
      *
      * @param arg The label-like string to be expanded, e.g. ":foo" or "//foo:bar"
-     * @param repositoryMapping map of {@code RepositoryName}s defined in the main workspace
+     * @param repositoryMapping map of apparent repository names to {@code RepositoryName}s
+     * @param workspaceRunfilesDirectory name of the runfiles directory corresponding to the main
+     *     repository
      * @return The expanded value
      */
-    public String apply(String arg, RepositoryMapping repositoryMapping) {
+    public String apply(
+        String arg, RepositoryMapping repositoryMapping, String workspaceRunfilesDirectory) {
       Label label;
       try {
         label = root.getRelativeWithRemapping(arg, repositoryMapping);
@@ -271,14 +287,13 @@ public String apply(String arg, RepositoryMapping repositoryMapping) {
             String.format(
                 "invalid label in %s expression: %s", functionName(), e.getMessage()), e);
       }
-      Collection<String> paths = resolveLabel(label);
+      Set<String> paths = resolveLabel(label, workspaceRunfilesDirectory);
       return joinPaths(paths);
     }
 
-    /**
-     * Returns all target location(s) of the given label.
-     */
-    private Collection<String> resolveLabel(Label unresolved) throws IllegalStateException {
+    /** Returns all target location(s) of the given label. */
+    private Set<String> resolveLabel(Label unresolved, String workspaceRunfilesDirectory)
+        throws IllegalStateException {
       Collection<Artifact> artifacts = locationMapSupplier.get().get(unresolved);
 
       if (artifacts == null) {
@@ -288,7 +303,7 @@ private Collection<String> resolveLabel(Label unresolved) throws IllegalStateExc
                 unresolved, functionName()));
       }
 
-      Set<String> paths = getPaths(artifacts);
+      Set<String> paths = getPaths(artifacts, workspaceRunfilesDirectory);
       if (paths.isEmpty()) {
         throw new IllegalStateException(
             String.format(
@@ -313,24 +328,41 @@ private Collection<String> resolveLabel(Label unresolved) throws IllegalStateExc
      * Extracts list of all executables associated with given collection of label artifacts.
      *
      * @param artifacts to get the paths of
+     * @param workspaceRunfilesDirectory name of the runfiles directory corresponding to the main
+     *     repository
      * @return all associated executable paths
      */
-    private Set<String> getPaths(Collection<Artifact> artifacts) {
+    private Set<String> getPaths(
+        Collection<Artifact> artifacts, String workspaceRunfilesDirectory) {
       TreeSet<String> paths = Sets.newTreeSet();
       for (Artifact artifact : artifacts) {
-        PathFragment execPath =
-            execPaths
-                ? artifact.getExecPath()
-                : legacyExternalRunfiles
-                    ? artifact.getPathForLocationExpansion()
-                    : artifact.getRunfilesPath();
-        if (execPath != null) {  // omit middlemen etc
-          paths.add(execPath.getCallablePathString());
+        PathFragment path = getPath(artifact, workspaceRunfilesDirectory);
+        if (path != null) { // omit middlemen etc
+          paths.add(path.getCallablePathString());
         }
       }
       return paths;
     }
 
+    private PathFragment getPath(Artifact artifact, String workspaceRunfilesDirectory) {
+      switch (pathType) {
+        case LOCATION:
+          return legacyExternalRunfiles
+              ? artifact.getPathForLocationExpansion()
+              : artifact.getRunfilesPath();
+        case EXEC:
+          return artifact.getExecPath();
+        case RLOCATION:
+          PathFragment runfilesPath = artifact.getRunfilesPath();
+          if (runfilesPath.startsWith(LabelConstants.EXTERNAL_RUNFILES_PATH_PREFIX)) {
+            return runfilesPath.relativeTo(LabelConstants.EXTERNAL_RUNFILES_PATH_PREFIX);
+          } else {
+            return PathFragment.create(workspaceRunfilesDirectory).getRelative(runfilesPath);
+          }
+      }
+      throw new IllegalStateException("Unexpected PathType: " + pathType);
+    }
+
     private String joinPaths(Collection<String> paths) {
       return paths.stream().map(ShellEscaper::escapeString).collect(joining(" "));
     }
@@ -348,27 +380,44 @@ static ImmutableMap<String, LocationFunction> allLocationFunctions(
     return new ImmutableMap.Builder<String, LocationFunction>()
         .put(
             "location",
-            new LocationFunction(root, locationMap, execPaths, legacyExternalRunfiles, EXACTLY_ONE))
+            new LocationFunction(
+                root,
+                locationMap,
+                execPaths ? PathType.EXEC : PathType.LOCATION,
+                legacyExternalRunfiles,
+                EXACTLY_ONE))
         .put(
             "locations",
             new LocationFunction(
-                root, locationMap, execPaths, legacyExternalRunfiles, ALLOW_MULTIPLE))
+                root,
+                locationMap,
+                execPaths ? PathType.EXEC : PathType.LOCATION,
+                legacyExternalRunfiles,
+                ALLOW_MULTIPLE))
         .put(
             "rootpath",
             new LocationFunction(
-                root, locationMap, USE_LOCATION_PATHS, legacyExternalRunfiles, EXACTLY_ONE))
+                root, locationMap, PathType.LOCATION, legacyExternalRunfiles, EXACTLY_ONE))
         .put(
             "rootpaths",
             new LocationFunction(
-                root, locationMap, USE_LOCATION_PATHS, legacyExternalRunfiles, ALLOW_MULTIPLE))
+                root, locationMap, PathType.LOCATION, legacyExternalRunfiles, ALLOW_MULTIPLE))
         .put(
             "execpath",
             new LocationFunction(
-                root, locationMap, USE_EXEC_PATHS, legacyExternalRunfiles, EXACTLY_ONE))
+                root, locationMap, PathType.EXEC, legacyExternalRunfiles, EXACTLY_ONE))
         .put(
             "execpaths",
             new LocationFunction(
-                root, locationMap, USE_EXEC_PATHS, legacyExternalRunfiles, ALLOW_MULTIPLE))
+                root, locationMap, PathType.EXEC, legacyExternalRunfiles, ALLOW_MULTIPLE))
+        .put(
+            "rlocationpath",
+            new LocationFunction(
+                root, locationMap, PathType.RLOCATION, legacyExternalRunfiles, EXACTLY_ONE))
+        .put(
+            "rlocationpaths",
+            new LocationFunction(
+                root, locationMap, PathType.RLOCATION, legacyExternalRunfiles, ALLOW_MULTIPLE))
         .buildOrThrow();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/LocationTemplateContext.java b/src/main/java/com/google/devtools/build/lib/analysis/LocationTemplateContext.java
index f3e66781c7dec3..0de4a4e498c49b 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/LocationTemplateContext.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/LocationTemplateContext.java
@@ -50,6 +50,7 @@ final class LocationTemplateContext implements TemplateContext {
   private final ImmutableMap<String, LocationFunction> functions;
   private final RepositoryMapping repositoryMapping;
   private final boolean windowsPath;
+  private final String workspaceRunfilesDirectory;
 
   private LocationTemplateContext(
       TemplateContext delegate,
@@ -58,12 +59,14 @@ private LocationTemplateContext(
       boolean execPaths,
       boolean legacyExternalRunfiles,
       RepositoryMapping repositoryMapping,
-      boolean windowsPath) {
+      boolean windowsPath,
+      String workspaceRunfilesDirectory) {
     this.delegate = delegate;
     this.functions =
         LocationExpander.allLocationFunctions(root, locationMap, execPaths, legacyExternalRunfiles);
     this.repositoryMapping = repositoryMapping;
     this.windowsPath = windowsPath;
+    this.workspaceRunfilesDirectory = workspaceRunfilesDirectory;
   }
 
   public LocationTemplateContext(
@@ -83,7 +86,8 @@ public LocationTemplateContext(
         execPaths,
         ruleContext.getConfiguration().legacyExternalRunfiles(),
         ruleContext.getRule().getPackage().getRepositoryMapping(),
-        windowsPath);
+        windowsPath,
+        ruleContext.getWorkspaceName());
   }
 
   @Override
@@ -108,7 +112,7 @@ private String lookupFunctionImpl(String name, String param) throws ExpansionExc
     try {
       LocationFunction f = functions.get(name);
       if (f != null) {
-        return f.apply(param, repositoryMapping);
+        return f.apply(param, repositoryMapping, workspaceRunfilesDirectory);
       }
     } catch (IllegalStateException e) {
       throw new ExpansionException(e.getMessage(), e);


Test patch:
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderIntegrationTest.java b/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderIntegrationTest.java
index 4f40434ea75b74..7a31156694281c 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderIntegrationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderIntegrationTest.java
@@ -17,6 +17,7 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
+import com.google.devtools.build.lib.testutil.TestConstants;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.ModifiedFileSet;
 import com.google.devtools.build.lib.vfs.Root;
@@ -121,6 +122,12 @@ public void otherPathExpansion() throws Exception {
         "genrule(name='foo', outs=['foo.txt'], cmd='never executed')",
         "sh_library(name='lib', srcs=[':foo'])");
 
+    FileSystemUtils.appendIsoLatin1(scratch.resolve("WORKSPACE"), "workspace(name='workspace')");
+    // Invalidate WORKSPACE to pick up the name.
+    getSkyframeExecutor()
+        .invalidateFilesUnderPathForTesting(
+            reporter, ModifiedFileSet.EVERYTHING_MODIFIED, Root.fromPath(rootDirectory));
+
     LocationExpander expander = makeExpander("//expansion:lib");
     assertThat(expander.expand("foo $(execpath :foo) bar"))
         .matches("foo .*-out/.*/expansion/foo\\.txt bar");
@@ -130,6 +137,22 @@ public void otherPathExpansion() throws Exception {
         .matches("foo expansion/foo.txt bar");
     assertThat(expander.expand("foo $(rootpaths :foo) bar"))
         .matches("foo expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath :foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths :foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath //expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths //expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @//expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths @//expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @workspace//expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths @workspace//expansion:foo) bar"))
+        .isEqualTo("foo workspace/expansion/foo.txt bar");
   }
 
   @Test
@@ -158,6 +181,10 @@ public void otherPathExternalExpansion() throws Exception {
         .matches("foo external/r/p/foo.txt bar");
     assertThat(expander.expand("foo $(rootpaths @r//p:foo) bar"))
         .matches("foo external/r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
   }
 
   @Test
@@ -183,6 +210,10 @@ public void otherPathExternalExpansionNoLegacyExternalRunfiles() throws Exceptio
         .matches("foo .*-out/.*/external/r/p/foo\\.txt bar");
     assertThat(expander.expand("foo $(rootpath @r//p:foo) bar")).matches("foo ../r/p/foo.txt bar");
     assertThat(expander.expand("foo $(rootpaths @r//p:foo) bar")).matches("foo ../r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
   }
 
   @Test
@@ -210,6 +241,10 @@ public void otherPathExternalExpansionNoLegacyExternalRunfilesSiblingRepositoryL
         .matches("foo .*-out/r/.*/p/foo\\.txt bar");
     assertThat(expander.expand("foo $(rootpath @r//p:foo) bar")).matches("foo ../r/p/foo.txt bar");
     assertThat(expander.expand("foo $(rootpaths @r//p:foo) bar")).matches("foo ../r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpath @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths @r//p:foo) bar"))
+        .isEqualTo("foo r/p/foo.txt bar");
   }
 
   @Test
@@ -224,5 +259,9 @@ public void otherPathMultiExpansion() throws Exception {
         .matches("foo .*-out/.*/expansion/bar\\.txt .*-out/.*/expansion/foo\\.txt bar");
     assertThat(expander.expand("foo $(rootpaths :foo) bar"))
         .matches("foo expansion/bar.txt expansion/foo.txt bar");
+    assertThat(expander.expand("foo $(rlocationpaths :foo) bar"))
+        .isEqualTo(
+            "foo __main__/expansion/bar.txt __main__/expansion/foo.txt bar"
+                .replace("__main__", TestConstants.WORKSPACE_NAME));
   }
 }
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderTest.java b/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderTest.java
index abdeb1ed742df4..9e6b63490ef638 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/LocationExpanderTest.java
@@ -59,22 +59,25 @@ public boolean hasErrors() {
   }
 
   private LocationExpander makeExpander(RuleErrorConsumer ruleErrorConsumer) throws Exception {
-    LocationFunction f1 = new LocationFunctionBuilder("//a", false)
-        .setExecPaths(false)
-        .add("//a", "/exec/src/a")
-        .build();
-
-    LocationFunction f2 = new LocationFunctionBuilder("//b", true)
-        .setExecPaths(false)
-        .add("//b", "/exec/src/b")
-        .build();
+    LocationFunction f1 =
+        new LocationFunctionBuilder("//a", false)
+            .setPathType(LocationFunction.PathType.LOCATION)
+            .add("//a", "/exec/src/a")
+            .build();
+
+    LocationFunction f2 =
+        new LocationFunctionBuilder("//b", true)
+            .setPathType(LocationFunction.PathType.LOCATION)
+            .add("//b", "/exec/src/b")
+            .build();
 
     return new LocationExpander(
         ruleErrorConsumer,
         ImmutableMap.<String, LocationFunction>of(
             "location", f1,
             "locations", f2),
-        RepositoryMapping.ALWAYS_FALLBACK);
+        RepositoryMapping.ALWAYS_FALLBACK,
+        "workspace");
   }
 
   private String expand(String input) throws Exception {
@@ -125,10 +128,11 @@ public void noExpansionOnError() throws Exception {
 
   @Test
   public void expansionWithRepositoryMapping() throws Exception {
-    LocationFunction f1 = new LocationFunctionBuilder("//a", false)
-        .setExecPaths(false)
-        .add("@bar//a", "/exec/src/a")
-        .build();
+    LocationFunction f1 =
+        new LocationFunctionBuilder("//a", false)
+            .setPathType(LocationFunction.PathType.LOCATION)
+            .add("@bar//a", "/exec/src/a")
+            .build();
 
     ImmutableMap<String, RepositoryName> repositoryMapping =
         ImmutableMap.of("foo", RepositoryName.create("bar"));
@@ -137,7 +141,8 @@ public void expansionWithRepositoryMapping() throws Exception {
         new LocationExpander(
             new Capture(),
             ImmutableMap.<String, LocationFunction>of("location", f1),
-            RepositoryMapping.createAllowingFallback(repositoryMapping));
+            RepositoryMapping.createAllowingFallback(repositoryMapping),
+            "workspace");
 
     String value = locationExpander.expand("$(location @foo//a)");
     assertThat(value).isEqualTo("src/a");
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
index 38addac4979d01..608b39b34fa105 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
@@ -49,16 +49,16 @@ public class LocationFunctionTest {
   public void absoluteAndRelativeLabels() throws Exception {
     LocationFunction func =
         new LocationFunctionBuilder("//foo", false).add("//foo", "/exec/src/bar").build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK)).isEqualTo("src/bar");
-    assertThat(func.apply(":foo", RepositoryMapping.ALWAYS_FALLBACK)).isEqualTo("src/bar");
-    assertThat(func.apply("foo", RepositoryMapping.ALWAYS_FALLBACK)).isEqualTo("src/bar");
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null)).isEqualTo("src/bar");
+    assertThat(func.apply(":foo", RepositoryMapping.ALWAYS_FALLBACK, null)).isEqualTo("src/bar");
+    assertThat(func.apply("foo", RepositoryMapping.ALWAYS_FALLBACK, null)).isEqualTo("src/bar");
   }
 
   @Test
   public void pathUnderExecRootUsesDotSlash() throws Exception {
     LocationFunction func =
         new LocationFunctionBuilder("//foo", false).add("//foo", "/exec/bar").build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK)).isEqualTo("./bar");
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null)).isEqualTo("./bar");
   }
 
   @Test
@@ -67,7 +67,7 @@ public void noSuchLabel() throws Exception {
     IllegalStateException expected =
         assertThrows(
             IllegalStateException.class,
-            () -> func.apply("//bar", RepositoryMapping.ALWAYS_FALLBACK));
+            () -> func.apply("//bar", RepositoryMapping.ALWAYS_FALLBACK, null));
     assertThat(expected)
         .hasMessageThat()
         .isEqualTo(
@@ -81,7 +81,7 @@ public void emptyList() throws Exception {
     IllegalStateException expected =
         assertThrows(
             IllegalStateException.class,
-            () -> func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK));
+            () -> func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null));
     assertThat(expected)
         .hasMessageThat()
         .isEqualTo("label '//foo:foo' in $(location) expression expands to no files");
@@ -94,7 +94,7 @@ public void tooMany() throws Exception {
     IllegalStateException expected =
         assertThrows(
             IllegalStateException.class,
-            () -> func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK));
+            () -> func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null));
     assertThat(expected)
         .hasMessageThat()
         .isEqualTo(
@@ -109,7 +109,7 @@ public void noSuchLabelMultiple() throws Exception {
     IllegalStateException expected =
         assertThrows(
             IllegalStateException.class,
-            () -> func.apply("//bar", RepositoryMapping.ALWAYS_FALLBACK));
+            () -> func.apply("//bar", RepositoryMapping.ALWAYS_FALLBACK, null));
     assertThat(expected)
         .hasMessageThat()
         .isEqualTo(
@@ -121,7 +121,7 @@ public void noSuchLabelMultiple() throws Exception {
   public void fileWithSpace() throws Exception {
     LocationFunction func =
         new LocationFunctionBuilder("//foo", false).add("//foo", "/exec/file/with space").build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK))
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null))
         .isEqualTo("'file/with space'");
   }
 
@@ -130,7 +130,7 @@ public void multipleFiles() throws Exception {
     LocationFunction func = new LocationFunctionBuilder("//foo", true)
         .add("//foo", "/exec/foo/bar", "/exec/out/foo/foobar")
         .build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK))
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null))
         .isEqualTo("foo/bar foo/foobar");
   }
 
@@ -139,27 +139,41 @@ public void filesWithSpace() throws Exception {
     LocationFunction func = new LocationFunctionBuilder("//foo", true)
         .add("//foo", "/exec/file/with space", "/exec/file/with spaces ")
         .build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK))
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null))
         .isEqualTo("'file/with space' 'file/with spaces '");
   }
 
   @Test
   public void execPath() throws Exception {
-    LocationFunction func = new LocationFunctionBuilder("//foo", true)
-        .setExecPaths(true)
-        .add("//foo", "/exec/bar", "/exec/out/foobar")
-        .build();
-    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK))
+    LocationFunction func =
+        new LocationFunctionBuilder("//foo", true)
+            .setPathType(LocationFunction.PathType.EXEC)
+            .add("//foo", "/exec/bar", "/exec/out/foobar")
+            .build();
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, null))
         .isEqualTo("./bar out/foobar");
   }
 
+  @Test
+  public void rlocationPath() throws Exception {
+    LocationFunction func =
+        new LocationFunctionBuilder("//foo", true)
+            .setPathType(LocationFunction.PathType.RLOCATION)
+            .add("//foo", "/exec/bar", "/exec/out/foobar")
+            .build();
+    assertThat(func.apply("//foo", RepositoryMapping.ALWAYS_FALLBACK, "workspace"))
+        .isEqualTo("workspace/bar workspace/foobar");
+  }
+
   @Test
   public void locationFunctionWithMappingReplace() throws Exception {
     RepositoryName b = RepositoryName.create("b");
     ImmutableMap<String, RepositoryName> repositoryMapping = ImmutableMap.of("a", b);
     LocationFunction func =
         new LocationFunctionBuilder("//foo", false).add("@b//foo", "/exec/src/bar").build();
-    assertThat(func.apply("@a//foo", RepositoryMapping.createAllowingFallback(repositoryMapping)))
+    assertThat(
+            func.apply(
+                "@a//foo", RepositoryMapping.createAllowingFallback(repositoryMapping), null))
         .isEqualTo("src/bar");
   }
 
@@ -170,7 +184,8 @@ public void locationFunctionWithMappingIgnoreRepo() throws Exception {
     LocationFunction func =
         new LocationFunctionBuilder("//foo", false).add("@potato//foo", "/exec/src/bar").build();
     assertThat(
-            func.apply("@potato//foo", RepositoryMapping.createAllowingFallback(repositoryMapping)))
+            func.apply(
+                "@potato//foo", RepositoryMapping.createAllowingFallback(repositoryMapping), null))
         .isEqualTo("src/bar");
   }
 }
@@ -178,7 +193,7 @@ public void locationFunctionWithMappingIgnoreRepo() throws Exception {
 final class LocationFunctionBuilder {
   private final Label root;
   private final boolean multiple;
-  private boolean execPaths;
+  private LocationFunction.PathType pathType = LocationFunction.PathType.LOCATION;
   private boolean legacyExternalRunfiles;
   private final Map<Label, Collection<Artifact>> labelMap = new HashMap<>();
 
@@ -189,12 +204,12 @@ final class LocationFunctionBuilder {
 
   public LocationFunction build() {
     return new LocationFunction(
-        root, Suppliers.ofInstance(labelMap), execPaths, legacyExternalRunfiles, multiple);
+        root, Suppliers.ofInstance(labelMap), pathType, legacyExternalRunfiles, multiple);
   }
 
   @CanIgnoreReturnValue
-  public LocationFunctionBuilder setExecPaths(boolean execPaths) {
-    this.execPaths = execPaths;
+  public LocationFunctionBuilder setPathType(LocationFunction.PathType pathType) {
+    this.pathType = pathType;
     return this;
   }
 
diff --git a/src/test/py/bazel/runfiles_test.py b/src/test/py/bazel/runfiles_test.py
index cb37929531360e..6c2692e58b1098 100644
--- a/src/test/py/bazel/runfiles_test.py
+++ b/src/test/py/bazel/runfiles_test.py
@@ -312,6 +312,41 @@ def testLegacyExternalRunfilesOption(self):
                                    "bin/bin.runfiles_manifest")
     self.AssertFileContentNotContains(manifest_path, "__main__/external/A")
 
+  def testRunfilesLibrariesFindRlocationpathExpansion(self):
+    self.ScratchDir("A")
+    self.ScratchFile("A/WORKSPACE")
+    self.ScratchFile("A/p/BUILD", ["exports_files(['foo.txt'])"])
+    self.ScratchFile("A/p/foo.txt", ["Hello, World!"])
+    self.ScratchFile("WORKSPACE", ["local_repository(name = 'A', path='A')"])
+    self.ScratchFile("pkg/BUILD", [
+        "py_binary(",
+        "  name = 'bin',",
+        "  srcs = ['bin.py'],",
+        "  args = [",
+        "    '$(rlocationpath bar.txt)',",
+        "    '$(rlocationpath @A//p:foo.txt)',",
+        "  ],",
+        "  data = [",
+        "    'bar.txt',",
+        "    '@A//p:foo.txt'",
+        "  ],",
+        "  deps = ['@bazel_tools//tools/python/runfiles'],",
+        ")",
+    ])
+    self.ScratchFile("pkg/bar.txt", ["Hello, Bazel!"])
+    self.ScratchFile("pkg/bin.py", [
+        "import sys",
+        "from tools.python.runfiles import runfiles",
+        "r = runfiles.Create()",
+        "for arg in sys.argv[1:]:",
+        "  print(open(r.Rlocation(arg)).read().strip())",
+    ])
+    _, stdout, _ = self.RunBazel(["run", "//pkg:bin"])
+    if len(stdout) != 2:
+      self.fail("stdout: %s" % stdout)
+    self.assertEqual(stdout[0], "Hello, Bazel!")
+    self.assertEqual(stdout[1], "Hello, World!")
+
 
 if __name__ == "__main__":
   unittest.main()