feat: add to_output_relative_path

This is useful in rules_js ecosystem where the working directory is bazel-out/arch/bin so many paths need to be relative to there.

.bazelignore

@@ -0,0 +1 @@
+e2e/

WORKSPACE

@@ -25,12 +25,6 @@ local_repository(
     path = "./lib/tests/external_test_repo",
 )
 
-# Avoid descending into the e2e workspaces
-local_repository(
-    name = "e2e_bzlmod",
-    path = "./e2e/bzlmod",
-)
-
 ############################################
 # Gazelle, for generating bzl_library targets
 load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_dependencies")

docs/paths.md

@@ -56,6 +56,24 @@ in order to locate entries by their key.
 The runfiles manifest entry path for a file
 
 
+<a id="to_output_relative_path"></a>
+
+## to_output_relative_path
+
+<pre>
+to_output_relative_path(<a href="#to_output_relative_path-f">f</a>)
+</pre>
+
+The relative path from bazel-out/[arch]/bin to the given File object
+
+**PARAMETERS**
+
+
+| Name  | Description | Default Value |
+| :------------- | :------------- | :------------- |
+| <a id="to_output_relative_path-f"></a>f |  <p align="center"> - </p>   |  none |
+
+
 <a id="to_workspace_path"></a>
 
 ## to_workspace_path

lib/paths.bzl

@@ -5,6 +5,7 @@ load("//lib/private:paths.bzl", "paths")
 relative_file = paths.relative_file
 to_manifest_path = paths.to_manifest_path
 to_workspace_path = paths.to_workspace_path
+to_output_relative_path = paths.to_output_relative_path
 
 # Bash helper function for looking up runfiles.
 # See windows_utils.bzl for the cmd.exe equivalent.

lib/private/paths.bzl

@@ -42,6 +42,18 @@ def _relative_file(to_file, frm_file):
         )
     )
 
+def _to_output_relative_path(f):
+    "The relative path from bazel-out/[arch]/bin to the given File object"
+    if f.is_source:
+        execroot = "../../../"
+    else:
+        execroot = ""
+    if f.short_path.startswith("../"):
+        path = "external/" + f.short_path[3:]
+    else:
+        path = f.short_path
+    return execroot + path
+
 def _to_manifest_path(ctx, file):
     """The runfiles manifest entry path for a file
 
@@ -87,5 +99,6 @@ def _to_workspace_path(file):
 paths = struct(
     relative_file = _relative_file,
     to_manifest_path = _to_manifest_path,
+    to_output_relative_path = _to_output_relative_path,
     to_workspace_path = _to_workspace_path,
 )

lib/tests/paths_test.bzl

@@ -128,13 +128,28 @@ def _workspace_path_test_impl(ctx):
     asserts.equals(env, "lib/paths.bzl", paths.to_workspace_path(ctx.file.f2))
     return unittest.end(env)
 
+def _output_relative_path_test_impl(ctx):
+    env = unittest.begin(ctx)
+    asserts.equals(env, "../../../external/bazel_skylib/LICENSE", paths.to_output_relative_path(ctx.file.f1))
+    asserts.equals(env, "../../../lib/paths.bzl", paths.to_output_relative_path(ctx.file.f2))
+    asserts.equals(env, "external/external_test_repo/test_a", paths.to_output_relative_path(ctx.file.f3))
+    asserts.equals(env, "lib/tests/template.txt", paths.to_output_relative_path(ctx.file.f4))
+    return unittest.end(env)
+
 _ATTRS = {
+    # source file in external repo
     "f1": attr.label(allow_single_file = True, default = "@bazel_skylib//:LICENSE"),
+    # source file in current repo
     "f2": attr.label(allow_single_file = True, default = "//lib:paths.bzl"),
+    # output file in external repo
+    "f3": attr.label(allow_single_file = True, default = "@external_test_repo//:test_a"),
+    # output file in current repo
+    "f4": attr.label(allow_single_file = True, default = "//lib/tests:gen_template"),
 }
 
 relative_file_test = unittest.make(_relative_file_test_impl)
 manifest_path_test = unittest.make(_manifest_path_test_impl, attrs = _ATTRS)
+output_relative_path_test = unittest.make(_output_relative_path_test_impl, attrs = _ATTRS)
 workspace_path_test = unittest.make(_workspace_path_test_impl, attrs = _ATTRS)
 
 def paths_test_suite():
@@ -142,5 +157,6 @@ def paths_test_suite():
         "paths_tests",
         relative_file_test,
         manifest_path_test,
+        output_relative_path_test,
         workspace_path_test,
     )