Improve Gazelle launcher's runfiles discovery on Windows

The Bash runfiles library consumes paths of the form
`repo/path/to/pkg/file` and is more reliable than the custom runfiles
discovery function.

Co-authored-by: Shashank <[email protected]>

def.bzl

@@ -63,6 +63,12 @@ def _valid_env_variable_name(name):
         return False
     return True
 
+def _rlocation_path(ctx, file):
+    if file.short_path.startswith("../"):
+        return file.short_path[3:]
+    else:
+        return ctx.workspace_name + "/" + file.short_path
+
 def _gazelle_runner_impl(ctx):
     args = [ctx.attr.command]
     if ctx.attr.mode:
@@ -88,16 +94,14 @@ def _gazelle_runner_impl(ctx):
     repo_config = ctx.file._repo_config
     substitutions = {
         "@@ARGS@@": shell.array_literal(args),
-        "@@GAZELLE_LABEL@@": shell.quote(str(ctx.attr.gazelle.label)),
-        "@@GAZELLE_SHORT_PATH@@": shell.quote(ctx.executable.gazelle.short_path),
+        "@@GAZELLE_PATH@@": shell.quote(_rlocation_path(ctx, ctx.executable.gazelle)),
         "@@GENERATED_MESSAGE@@": """
 # Generated by {label}
 # DO NOT EDIT
 """.format(label = str(ctx.label)),
-        "@@RUNNER_LABEL@@": shell.quote(str(ctx.label)),
-        "@@GOTOOL@@": shell.quote(go_tool.short_path),
+        "@@GOTOOL@@": shell.quote(_rlocation_path(ctx, go_tool)),
         "@@ENV@@": env,
-        "@@REPO_CONFIG_SHORT_PATH@@": shell.quote(repo_config.short_path) if repo_config else "",
+        "@@REPO_CONFIG_PATH@@": shell.quote(_rlocation_path(ctx, repo_config)) if repo_config else "",
     }
     ctx.actions.expand_template(
         template = ctx.file._template,
@@ -186,5 +190,6 @@ def gazelle(name, **kwargs):
         srcs = [runner_name],
         tags = tags,
         visibility = visibility,
+        deps = ["@bazel_tools//tools/bash/runfiles"],
         data = kwargs["data"] if "data" in kwargs else [],
     )

internal/gazelle.bash.in

@@ -14,41 +14,34 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# --- begin runfiles.bash initialization v3 ---
+# Copy-pasted from the Bazel Bash runfiles library v3.
+set -uo pipefail; set +e; 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 v3 ---
+
 @@GENERATED_MESSAGE@@
 
 set -euo pipefail
 
-RUNNER_LABEL=@@RUNNER_LABEL@@
-GAZELLE_SHORT_PATH=@@GAZELLE_SHORT_PATH@@
-GAZELLE_LABEL=@@GAZELLE_LABEL@@
+GAZELLE_PATH=@@GAZELLE_PATH@@
 ARGS=@@ARGS@@
 GOTOOL=@@GOTOOL@@
-REPO_CONFIG_SHORT_PATH=@@REPO_CONFIG_SHORT_PATH@@
+REPO_CONFIG_PATH=@@REPO_CONFIG_PATH@@
 
 @@ENV@@
 
-# find_runfile prints the location of a runfile in the source workspace,
-# either by reading the symbolic link or reading the runfiles manifest.
-function find_runfile {
-  local runfile=$1
-  if [ -f "$runfile" ]; then
-    readlink "$runfile"
-    return
-  fi
-  runfile=${runfile#external/}
-  if grep -q "^$runfile" "$0.runfiles_manifest"; then
-    grep "^$runfile" "$0.runfiles_manifest" | head -n 1 | cut -d' ' -f2
-    return
-  fi
-  # printing nothing indicates failure
-}
-
 # set_goroot attempts to set GOROOT to the SDK used by rules_go. gazelle
 # invokes tools inside the Go SDK for dependency management. It's good to
 # use the SDK used by the workspace in case the Go SDK is not installed
 # on the host system or is a different version.
 function set_goroot {
-  local gotool=$(find_runfile "$GOTOOL")
+  local gotool=$(rlocation "$GOTOOL")
   if [ -z "$gotool" ]; then
     echo "$0: warning: could not locate GOROOT used by rules_go" >&2
     return
@@ -76,8 +69,8 @@ esac
 # able to find runfiles, and some extensions rely on that. Gazelle can use
 # BUILD_WORKSPACE_DIRECTORY to interpret relative paths on the command line.
 set_goroot
-gazelle_short_path=$(find_runfile "$GAZELLE_SHORT_PATH")
-if [ -z "$gazelle_short_path" ]; then
+gazelle_path=$(rlocation "$GAZELLE_PATH")
+if [ -z "$gazelle_path" ]; then
   echo "error: could not locate gazelle binary" >&2
   exit 1
 fi
@@ -101,8 +94,8 @@ fi
 # When running with Bzlmod, there is no WORKSPACE file for Gazelle to read
 # the definitions of go_repository rules from. Instead, we pass the path to
 # the repo config file as a flag.
-if [[ "${is_fix_or_update:-}" == "true"  ]] && [[ -n $REPO_CONFIG_SHORT_PATH ]]; then
-  ARGS=("${ARGS[0]}" "-repo_config" "$(find_runfile "$REPO_CONFIG_SHORT_PATH")" "${ARGS[@]:1}")
+if [[ "${is_fix_or_update:-}" == "true"  ]] && [[ -n $REPO_CONFIG_PATH ]]; then
+  ARGS=("${ARGS[0]}" "-repo_config" "$(rlocation "$REPO_CONFIG_PATH")" "${ARGS[@]:1}")
 fi
 
-"$gazelle_short_path" "${ARGS[@]}"
+"$gazelle_path" "${ARGS[@]}"