feat: add runfiles helpers needed for rules_js (#3)

* feat: add runfiles helpers needed for rules_js

* chore: code review feedback

docs/paths.md

@@ -25,3 +25,30 @@ Resolves a relative path between two files, "to_file" and "frm_file", they must
 The relative path from frm_file to to_file, including the file name
 
 
+<a id="#to_manifest_path"></a>
+
+## to_manifest_path
+
+<pre>
+to_manifest_path(<a href="#to_manifest_path-ctx">ctx</a>, <a href="#to_manifest_path-file">file</a>)
+</pre>
+
+The runfiles manifest entry for a file
+
+We must avoid using non-normalized paths (workspace/../other_workspace/path)
+in order to locate entries by their key.
+
+
+**PARAMETERS**
+
+
+| Name  | Description | Default Value |
+| :------------- | :------------- | :------------- |
+| <a id="to_manifest_path-ctx"></a>ctx |  starlark rule execution context   |  none |
+| <a id="to_manifest_path-file"></a>file |  a File object   |  none |
+
+**RETURNS**
+
+a key that can lookup the path from the runfiles manifest
+
+

lib/expand_make_vars.bzl

@@ -9,4 +9,9 @@ load(
 
 expand_locations = _expand_locations
 expand_variables = _expand_variables
-expand_template = _expand_template
+
+expand_template = rule(
+    doc = _expand_template.doc,
+    implementation = _expand_template.implementation,
+    attrs = _expand_template.attrs,
+)

lib/paths.bzl

@@ -3,3 +3,20 @@
 load("//lib/private:paths.bzl", "paths")
 
 relative_file = paths.relative_file
+to_manifest_path = paths.to_manifest_path
+
+# Bash helper function for looking up runfiles.
+# See windows_utils.bzl for the cmd.exe equivalent.
+# Vendored from 
+# https://github.com/bazelbuild/bazel/blob/master/tools/bash/runfiles/runfiles.bash
+BASH_RLOCATION_FUNCTION = r"""
+# --- begin runfiles.bash initialization v2 ---
+set -uo pipefail; f=bazel_tools/tools/bash/runfiles/runfiles.bash
+source "${RUNFILES_DIR:-/dev/null}/$f" 2>/dev/null || \
+source "$(grep -sm1 "^$f " "${RUNFILES_MANIFEST_FILE:-/dev/null}" | cut -f2- -d' ')" 2>/dev/null || \
+source "$0.runfiles/$f" 2>/dev/null || \
+source "$(grep -sm1 "^$f " "$0.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+source "$(grep -sm1 "^$f " "$0.exe.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+{ echo>&2 "ERROR: cannot find $f"; exit 1; }; f=; set -e
+# --- end runfiles.bash initialization v2 ---
+"""

lib/private/expand_make_vars.bzl

@@ -174,7 +174,7 @@ def _expand_template_impl(ctx):
         is_executable = ctx.attr.is_executable,
     )
 
-expand_template = rule(
+expand_template = struct(
     doc = """Template expansion
     
 This performs a simple search over the template file for the keys in substitutions,

lib/private/paths.bzl

@@ -42,6 +42,26 @@ def _relative_file(to_file, frm_file):
         )
     )
 
+def _to_manifest_path(ctx, file):
+    """The runfiles manifest entry for a file
+
+    We must avoid using non-normalized paths (workspace/../other_workspace/path)
+    in order to locate entries by their key.
+    
+    Args:
+        ctx: starlark rule execution context
+        file: a File object
+    
+    Returns:
+        a key that can lookup the path from the runfiles manifest
+    """
+
+    if file.short_path.startswith("../"):
+        return file.short_path[3:]
+    else:
+        return ctx.workspace_name + "/" + file.short_path
+
 paths = struct(
     relative_file = _relative_file,
+    to_manifest_path = _to_manifest_path,
 )

lib/tests/paths_test.bzl

@@ -116,7 +116,21 @@ def _relative_file_test_impl(ctx):
 
     return unittest.end(env)
 
+def _runfiles_manifest_test_impl(ctx):
+    env = unittest.begin(ctx)
+    asserts.equals(env, "bazel_skylib/LICENSE", paths.to_manifest_path(ctx, ctx.file.f1))
+    asserts.equals(env, "aspect_bazel_lib/lib/paths.bzl", paths.to_manifest_path(ctx, ctx.file.f2))
+    return unittest.end(env)
+
 relative_file_test = unittest.make(_relative_file_test_impl)
+runfiles_manifest_test = unittest.make(_runfiles_manifest_test_impl,
+attrs = {
+    "f1": attr.label(allow_single_file = True, default = "@bazel_skylib//:LICENSE"),
+    "f2": attr.label(allow_single_file = True, default = "//lib:paths.bzl"),
+})
 
 def paths_test_suite():
-    unittest.suite("relative_file_tests", relative_file_test)
+    unittest.suite(
+        "paths_tests",
+        relative_file_test,
+        runfiles_manifest_test)

lib/windows_utils.bzl

@@ -0,0 +1,52 @@
+"Helpers for rules running on windows"
+
+# cmd.exe function for looking up runfiles.
+# Equivalent of the BASH_RLOCATION_FUNCTION in paths.bzl.
+# Use this to write actions that don't require bash.
+# Originally by @meteorcloudy in
+# https://github.com/bazelbuild/rules_nodejs/commit/f06553a
+BATCH_RLOCATION_FUNCTION = r"""
+rem Usage of rlocation function:
+rem        call :rlocation <runfile_path> <abs_path>
+rem        The rlocation function maps the given <runfile_path> to its absolute
+rem        path and stores the result in a variable named <abs_path>.
+rem        This function fails if the <runfile_path> doesn't exist in mainifest
+rem        file.
+:: Start of rlocation
+goto :rlocation_end
+:rlocation
+if "%~2" equ "" (
+  echo>&2 ERROR: Expected two arguments for rlocation function.
+  exit 1
+)
+if "%RUNFILES_MANIFEST_ONLY%" neq "1" (
+  set %~2=%~1
+  exit /b 0
+)
+if exist "%RUNFILES_DIR%" (
+  set RUNFILES_MANIFEST_FILE=%RUNFILES_DIR%_manifest
+)
+if "%RUNFILES_MANIFEST_FILE%" equ "" (
+  set RUNFILES_MANIFEST_FILE=%~f0.runfiles\MANIFEST
+)
+if not exist "%RUNFILES_MANIFEST_FILE%" (
+  set RUNFILES_MANIFEST_FILE=%~f0.runfiles_manifest
+)
+set MF=%RUNFILES_MANIFEST_FILE:/=\%
+if not exist "%MF%" (
+  echo>&2 ERROR: Manifest file %MF% does not exist.
+  exit 1
+)
+set runfile_path=%~1
+for /F "tokens=2* usebackq" %%i in (`%SYSTEMROOT%\system32\findstr.exe /l /c:"!runfile_path! " "%MF%"`) do (
+  set abs_path=%%i
+)
+if "!abs_path!" equ "" (
+  echo>&2 ERROR: !runfile_path! not found in runfiles manifest
+  exit 1
+)
+set %~2=!abs_path!
+exit /b 0
+:rlocation_end
+:: End of rlocation
+"""