fix flock

WORKSPACE

@@ -53,4 +53,4 @@ load(
     zig_register_toolchains = "register_toolchains",
 )
 
-zig_register_toolchains()
+zig_register_toolchains(speed_first_safety_later="auto")

toolchain/defs.bzl

@@ -173,10 +173,9 @@ def register_toolchains(
 
 ZIG_TOOL_PATH = "tools/{zig_tool}"
 ZIG_TOOL_WRAPPER = """#!/bin/bash
-set -eu
-readonly _zig="{zig}"
+set -e
 
-if [[ -n "$TMPDIR" ]]; then
+if [[ -z "$TMPDIR" ]]; then
   _cache_prefix=$TMPDIR
 else
   _cache_prefix="$HOME/.cache"
@@ -188,7 +187,22 @@ export ZIG_LOCAL_CACHE_DIR="$_cache_prefix/bazel-zig-cc"
 export ZIG_GLOBAL_CACHE_DIR=$ZIG_LOCAL_CACHE_DIR
 
 # https://github.com/ziglang/zig/issues/9431
-exec {maybe_flock} "$_zig" "{zig_tool}" "$@"
+_flock=
+if [[ -n "{do_flock}" ]]; then
+  _flock=$(command -v flock || :)
+  if [[ -z "$_flock" && -x /usr/local/bin/flock ]]; then
+    _flock=/usr/local/bin/flock
+  else
+    >&2 echo "WARNING: flock not found, proceeding unsafely."
+    >&2 echo "If build fails, retry it."
+  fi
+fi
+
+if [[ -n "$_flock" ]]; then
+  exec "$_flock" "{zig}" "{zig}" "{zig_tool}" "$@"
+else
+  exec "{zig}" "{zig_tool}" "$@"
+fi
 """
 
 _ZIG_TOOLS = [
@@ -224,18 +238,17 @@ def _zig_repository_impl(repository_ctx):
     if repository_ctx.attr.speed_first_safety_later == "auto":
         do_flock = repository_ctx.os.name.lower().startswith("mac os")
     elif repository_ctx.attr.speed_first_safety_later == "yes":
-        do_flock = True
-    else:
         do_flock = False
+    else:
+        do_flock = True
 
-    maybe_flock = 'flock "${_zig}"' if do_flock else ""
     for zig_tool in _ZIG_TOOLS:
         repository_ctx.file(
             ZIG_TOOL_PATH.format(zig_tool = zig_tool),
             ZIG_TOOL_WRAPPER.format(
                 zig = str(repository_ctx.path("zig")),
                 zig_tool = zig_tool,
-                maybe_flock = maybe_flock,
+                do_flock = "1" if do_flock else "",
             ),
         )