Merge pull request #30213 from travisdowns/td-noblock-tools

tools: run clang-format/clang-tidy in a separate bazel output_base

Author: travisdowns

tools/bazel-tools/.gitignore

@@ -0,0 +1 @@
+.cache/

tools/bazel-tools/support/bazel-tool-trampoline.sh

@@ -52,9 +52,61 @@ debug "running $BAZEL_TOOL_TRAMPOLINE_TARGET"
 debug "bazel invoke cwd: $(pwd)"
 debug "target cwd      : $BAZEL_TOOL_TRAMPOLINE_CWD"
 
+# If BAZEL_TRAMPOLINE_PARALLEL=1 use a separate output_base so this tool can run
+# in parallel with the main bazel server without contending for the same lock.
+# Best for tools that need to run frequently and don't need a ton of files in
+# their output base. disk_cache will in general obviate the need to actually
+# rebuild anything.
+#
+# Determining the default output_base is tricky: `bazel info output_base` itself
+# takes the main server's lock, so if the main server is busy the query would
+# block (defeating the point). Strategy (keyed on cache existence):
+#   - No cache yet: no choice but to block — call `bazel info output_base` and
+#     seed the cache with the result.
+#   - Cache exists: try `bazel --noblock_for_lock info output_base` to
+#     opportunistically refresh the cache; on lock-held (exit 9) just use the
+#     cached value.
+if [[ ${BAZEL_TRAMPOLINE_PARALLEL:-0} -gt 0 ]]; then
+  cache_dir="$support_script_dir/../.cache"
+  cache_file="$cache_dir/output_base"
+  mkdir -p "$cache_dir"
+
+  if [[ ! -f $cache_file ]]; then
+    debug "output_base from: blocking bazel query (no cache yet)"
+    default_output_base="$(bazel info output_base)"
+    echo "$default_output_base" >"$cache_file"
+  else
+    # Bazel exits 9 (LOCK_HELD_NOBLOCK_FOR_LOCK) when --noblock_for_lock
+    # cannot acquire the server lock. Any other non-zero exit is a real
+    # error and should surface rather than silently falling back to cache.
+    rc=0
+    fresh=$(bazel --noblock_for_lock info output_base 2>/dev/null) || rc=$?
+    if ((rc == 0)); then
+      debug "output_base from: live bazel query (cache refreshed)"
+      default_output_base=$fresh
+      echo "$default_output_base" >"$cache_file"
+    elif ((rc == 9)); then
+      default_output_base="$(cat "$cache_file")"
+      debug "output_base from: cache ($cache_file, lock held)"
+    else
+      echo "ERROR: bazel-tool-trampoline.sh: bazel info output_base failed (exit $rc)" >&2
+      exit "$rc"
+    fi
+  fi
+
+  tool_output_base="${default_output_base}_rptool"
+  output_base_flag=(--output_base="$tool_output_base")
+
+  debug "tool output_base   : $tool_output_base"
+else
+  output_base_flag=()
+  debug "tool output_base   : (default)"
+fi
+
 # These flags are to hide a bunch of Bazel's built-in output.
 
-exec bazel run "$BAZEL_TOOL_TRAMPOLINE_TARGET" \
+exec bazel "${output_base_flag[@]}" \
+  run "$BAZEL_TOOL_TRAMPOLINE_TARGET" \
   --run_under=//tools/bazel-tools/support:run \
   --noshow_progress \
   --ui_event_filters=,+error,+fail \

tools/clang-format

@@ -1 +1 @@
-clang-tool.sh
+clang-tool-parallel.sh

tools/clang-tool-parallel.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# Copyright 2026 Redpanda Data, Inc.
+#
+# Use of this software is governed by the Business Source License
+# included in the file licenses/BSL.md
+#
+# As of the Change Date specified in that file, in accordance with
+# the Business Source License, use of this software will be governed
+# by the Apache License, Version 2.0
+
+# Variant of clang-tool.sh that runs the tool against a separate bazel
+# output_base so it can execute in parallel with the main bazel server.
+# Only suitable for tools that don't depend on bazel-built artifacts
+# (e.g. clang-tidy plugins) living in the default output_base.
+
+export BAZEL_TRAMPOLINE_PARALLEL="${BAZEL_TRAMPOLINE_PARALLEL:-1}"
+
+tools_dir="$(cd -- "$(dirname -- "$(realpath "${BASH_SOURCE[0]}")")" &>/dev/null && pwd)"
+
+# `exec -a` doesn't propagate through a shebang into bash's $0, so forward
+# the invocation name via an env var that clang-tool.sh consults.
+export CLANG_TOOL_NAME="$(basename "$0")"
+exec "$tools_dir/clang-tool.sh" "$@"

tools/clang-tool.sh

@@ -6,7 +6,8 @@
 
 tools_dir="$(cd -- "$(dirname -- "$(realpath "${BASH_SOURCE[0]}")")" &>/dev/null && pwd)"
 
-export BAZEL_TOOL_TRAMPOLINE_TARGET="@current_llvm_toolchain_llvm//:bin/$(basename "$0")"
+tool_name="${CLANG_TOOL_NAME:-$(basename "$0")}"
+export BAZEL_TOOL_TRAMPOLINE_TARGET="@current_llvm_toolchain_llvm//:bin/$tool_name"
 
 if [[ ${BAZEL_TRAMPOLINE_DEBUG:-0} -gt 0 ]]; then
   echo "DEBUG: clang-tool.sh: CWD        : $(pwd)" >&2