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launcher.zig
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launcher.zig
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// Copyright 2023 Uber Technologies, Inc.
// Licensed under the Apache License, Version 2.0
//
// A wrapper for `zig` subcommands.
//
// In simple cases it is usually enough to:
//
// zig c++ -target <triple> <...>
//
// However, there are some caveats:
//
// * Sometimes toolchains (looking at you, Go, see an example in
// https://github.com/golang/go/pull/55966) skip CFLAGS to the underlying
// compiler. Doing that may carry a huge cost, because zig may need to spend
// ~30s compiling libc++ for an innocent feature test. Having an executable per
// target platform (like GCC does things, e.g. aarch64-linux-gnu-<tool>) is
// what most toolchains are designed to work with. So we need a wrapper per
// zig sub-command per target. As of writing, the layout is:
// tools/
// ├── x86_64-linux-gnu.2.34
// │ ├── ar
// │ ├── c++
// │ └── ld.lld
// ├── x86_64-linux-musl
// │ ├── ar
// │ ├── c++
// │ └── ld.lld
// ├── x86_64-macos-none
// │ ├── ar
// │ ├── c++
// │ └── ld64.lld
// ...
// * ZIG_LIB_DIR controls the output of `zig c++ -MF -MD <...>`. Bazel uses
// command to understand which input files were used to the compilation. If any
// of the files are not in `external/<...>/`, Bazel will understand and
// complain that the compiler is using undeclared directories on the host file
// system. We do not declare prerequisites using absolute paths, because that
// busts Bazel's remote cache.
// * BAZEL_ZIG_CC_CACHE_PREFIX is configurable per toolchain instance, and
// ZIG_GLOBAL_CACHE_DIR and ZIG_LOCAL_CACHE_DIR must be set to its value for
// all `zig` invocations.
//
// Originally this was a Bash script, then a POSIX shell script, then two
// scripts (one with pre-defined BAZEL_ZIG_CC_CACHE_PREFIX, one without). Then
// Windows came along with two PowerShell scripts (ports of the POSIX shell
// scripts), which I kept breaking. Then Bazel 6 came with
// `--experimental_use_hermetic_linux_sandbox`, which hermetizes the sandbox to
// the extreme: the sandbox has nothing that is not declared. /bin/sh and its
// dependencies (/lib/x86_64-linux-gnu/libc.so.6 on my system) are obviously
// not declared. So one can either declare those dependencies, bundle a shell
// to execute the wrapper, or port the shell logic to a cross-platform program
// that compiles to a static binary. By a chance we happen to already ship a
// toolchain of a language that could compile such program. And behold, the
// program is below.
const builtin = @import("builtin");
const std = @import("std");
const fs = std.fs;
const mem = std.mem;
const process = std.process;
const ChildProcess = std.ChildProcess;
const ArrayListUnmanaged = std.ArrayListUnmanaged;
const sep = fs.path.sep_str;
const EXE = switch (builtin.target.os.tag) {
.windows => ".exe",
else => "",
};
const CACHE_DIR = "{BAZEL_ZIG_CC_CACHE_PREFIX}";
const usage_cpp =
\\
\\Usage: <...>/tools/<target-triple>/{[zig_tool]s}{[exe]s} <args>...
\\
\\Wraps the "zig" multi-call binary. It determines the target platform from
\\the directory where it was called. Then sets ZIG_LIB_DIR,
\\ZIG_GLOBAL_CACHE_DIR, ZIG_LOCAL_CACHE_DIR and then calls:
\\
\\ zig c++ -target <target-triple> <args>...
;
const usage_other =
\\Usage: <...>/tools/<target-triple>/{[zig_tool]s}{[exe]s} <args>...
\\
\\Wraps the "zig" multi-call binary. It sets ZIG_LIB_DIR,
\\ZIG_GLOBAL_CACHE_DIR, ZIG_LOCAL_CACHE_DIR, and then calls:
\\
\\ zig {[zig_tool]s} <args>...
;
const Action = enum {
err,
exec,
};
const ExecParams = struct {
args: ArrayListUnmanaged([]const u8),
env: process.EnvMap,
};
const ParseResults = union(Action) {
err: []const u8,
exec: ExecParams,
};
pub fn main() u8 {
const allocator = if (builtin.link_libc)
std.heap.c_allocator
else blk: {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
break :blk gpa.allocator();
};
var arena_allocator = std.heap.ArenaAllocator.init(allocator);
defer arena_allocator.deinit();
const arena = arena_allocator.allocator();
var argv_it = process.argsWithAllocator(arena) catch |err|
return fatal("error parsing args: {s}\n", .{@errorName(err)});
const action = parseArgs(arena, fs.cwd(), &argv_it) catch |err|
return fatal("error: {s}\n", .{@errorName(err)});
switch (action) {
.err => |msg| return fatal("{s}", .{msg}),
.exec => |params| {
if (builtin.os.tag == .windows)
return spawnWindows(arena, params)
else
return execUnix(arena, params);
},
}
}
fn spawnWindows(arena: mem.Allocator, params: ExecParams) u8 {
var proc = ChildProcess.init(params.args.items, arena);
proc.env_map = ¶ms.env;
const ret = proc.spawnAndWait() catch |err|
return fatal(
"error spawning {s}: {s}\n",
.{ params.args.items[0], @errorName(err) },
);
switch (ret) {
.Exited => |code| return code,
else => |other| return fatal("abnormal exit: {any}\n", .{other}),
}
}
fn execUnix(arena: mem.Allocator, params: ExecParams) u8 {
const err = process.execve(arena, params.args.items, ¶ms.env);
std.debug.print(
"error execing {s}: {s}\n",
.{ params.args.items[0], @errorName(err) },
);
return 1;
}
// argv_it is an object that has such method:
// fn next(self: *Self) ?[]const u8
// in non-testing code it is *process.ArgIterator.
// Leaks memory: the name of the first argument is arena not by chance.
fn parseArgs(
arena: mem.Allocator,
cwd: fs.Dir,
argv_it: anytype,
) error{OutOfMemory}!ParseResults {
const arg0 = argv_it.next() orelse
return parseFatal(arena, "error: argv[0] cannot be null", .{});
const zig_tool = blk: {
const b = fs.path.basename(arg0);
if (builtin.target.os.tag == .windows and
std.ascii.eqlIgnoreCase(".exe", b[b.len - 4 ..]))
break :blk b[0 .. b.len - 4];
break :blk b;
};
const maybe_target = getTarget(arg0) catch |err| switch (err) {
error.BadParent => {
const fmt_args = .{ .zig_tool = zig_tool, .exe = EXE };
if (mem.eql(u8, zig_tool, "c++"))
return parseFatal(arena, usage_cpp, fmt_args)
else
return parseFatal(arena, usage_other, fmt_args);
},
else => |e| return e,
};
const root = blk: {
var dir = cwd.openDir(
"external" ++ sep ++ "zig_sdk" ++ sep ++ "lib",
.{ .access_sub_paths = false, .no_follow = true },
);
if (dir) |*dir_exists| {
dir_exists.close();
break :blk "external" ++ sep ++ "zig_sdk";
} else |_| {}
// directory does not exist or there was an error opening it
const here = fs.path.dirname(arg0) orelse ".";
break :blk try fs.path.join(arena, &[_][]const u8{ here, "..", ".." });
};
const zig_lib_dir = try fs.path.join(arena, &[_][]const u8{ root, "lib" });
const zig_exe = try fs.path.join(
arena,
&[_][]const u8{ root, "zig" ++ EXE },
);
var env = process.getEnvMap(arena) catch |err|
return parseFatal(arena, "error getting env: {s}", .{@errorName(err)});
try env.put("ZIG_LIB_DIR", zig_lib_dir);
try env.put("ZIG_LOCAL_CACHE_DIR", CACHE_DIR);
try env.put("ZIG_GLOBAL_CACHE_DIR", CACHE_DIR);
// args is the path to the zig binary and args to it.
var args = ArrayListUnmanaged([]const u8){};
try args.appendSlice(arena, &[_][]const u8{ zig_exe, zig_tool });
if (maybe_target) |target|
try args.appendSlice(arena, &[_][]const u8{ "-target", target });
while (argv_it.next()) |arg|
try args.append(arena, arg);
return ParseResults{ .exec = .{ .args = args, .env = env } };
}
fn parseFatal(
arena: mem.Allocator,
comptime fmt: []const u8,
args: anytype,
) error{OutOfMemory}!ParseResults {
const msg = try std.fmt.allocPrint(arena, fmt ++ "\n", args);
return ParseResults{ .err = msg };
}
pub fn fatal(comptime fmt: []const u8, args: anytype) u8 {
std.debug.print(fmt, args);
return 1;
}
fn getTarget(self_exe: []const u8) error{BadParent}!?[]const u8 {
const here = fs.path.dirname(self_exe) orelse return error.BadParent;
const triple = fs.path.basename(here);
// Validating the triple now will help users catch errors even if they
// don't yet need the target. yes yes the validation will miss things
// strings `is.it.x86_64?-stallinux,macos-`; we are trying to aid users
// that run things from the wrong directory, not trying to punish the ones
// having fun.
var it = mem.split(u8, triple, "-");
const arch = it.next() orelse return error.BadParent;
if (mem.indexOf(u8, "aarch64,x86_64", arch) == null)
return error.BadParent;
const got_os = it.next() orelse return error.BadParent;
if (mem.indexOf(u8, "linux,macos,windows", got_os) == null)
return error.BadParent;
// ABI triple is too much of a moving target
if (it.next() == null) return error.BadParent;
// but the target needs to have 3 dashes.
if (it.next() != null) return error.BadParent;
if (mem.eql(u8, "c++" ++ EXE, fs.path.basename(self_exe)))
return triple
else
return null;
}
const testing = std.testing;
pub const TestArgIterator = struct {
index: usize = 0,
argv: []const [:0]const u8,
pub fn next(self: *TestArgIterator) ?[:0]const u8 {
if (self.index == self.argv.len) return null;
defer self.index += 1;
return self.argv[self.index];
}
};
fn compareExec(
res: ParseResults,
want_args: []const [:0]const u8,
want_env_zig_lib_dir: []const u8,
) !void {
try testing.expectEqual(want_args.len, res.exec.args.items.len);
for (want_args, res.exec.args.items) |want_arg, got_arg|
try testing.expectEqualStrings(want_arg, got_arg);
try testing.expectEqualStrings(
want_env_zig_lib_dir,
res.exec.env.get("ZIG_LIB_DIR").?,
);
}
test "launcher:parseArgs" {
// not using testing.allocator, because parseArgs is designed to be used
// with an arena.
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
var allocator = gpa.allocator();
const tests = [_]struct {
args: []const [:0]const u8,
precreate_dir: ?[]const u8 = null,
want_result: union(Action) {
err: []const u8,
exec: struct {
args: []const [:0]const u8,
env_zig_lib_dir: []const u8,
},
},
}{
.{
.args = &[_][:0]const u8{"ar" ++ EXE},
.want_result = .{
.err = std.fmt.comptimePrint(usage_other ++ "\n", .{
.zig_tool = "ar",
.exe = EXE,
}),
},
},
.{
.args = &[_][:0]const u8{"c++" ++ EXE},
.want_result = .{
.err = std.fmt.comptimePrint(usage_cpp ++ "\n", .{
.zig_tool = "c++",
.exe = EXE,
}),
},
},
.{
.args = &[_][:0]const u8{
"tools" ++ sep ++ "x86_64-linux-musl" ++ sep ++ "c++" ++ EXE,
"main.c",
"-o",
"/dev/null",
},
.want_result = .{
.exec = .{
.args = &[_][:0]const u8{
"tools" ++ sep ++ "x86_64-linux-musl" ++ sep ++
".." ++ sep ++ ".." ++ sep ++ "zig" ++ EXE,
"c++",
"-target",
"x86_64-linux-musl",
"main.c",
"-o",
"/dev/null",
},
.env_zig_lib_dir = "tools" ++ sep ++ "x86_64-linux-musl" ++
sep ++ ".." ++ sep ++ ".." ++ sep ++ "lib",
},
},
},
.{
.args = &[_][:0]const u8{
"tools" ++ sep ++ "x86_64-linux-musl" ++ sep ++ "ar" ++ EXE,
"-rcs",
"all.a",
"main.o",
"foo.o",
},
.want_result = .{
.exec = .{
.args = &[_][:0]const u8{
"tools" ++ sep ++ "x86_64-linux-musl" ++ sep ++ ".." ++
sep ++ ".." ++ sep ++ "zig" ++ EXE,
"ar",
"-rcs",
"all.a",
"main.o",
"foo.o",
},
.env_zig_lib_dir = "tools" ++ sep ++ "x86_64-linux-musl" ++
sep ++ ".." ++ sep ++ ".." ++ sep ++ "lib",
},
},
},
.{
.args = &[_][:0]const u8{
"external_zig_sdk" ++ sep ++ "tools" ++ sep ++
"x86_64-linux-gnu.2.28" ++ sep ++ "c++" ++ EXE,
"main.c",
"-o",
"/dev/null",
},
.precreate_dir = "external" ++ sep ++ "zig_sdk" ++ sep ++ "lib",
.want_result = .{
.exec = .{
.args = &[_][:0]const u8{
"external" ++ sep ++ "zig_sdk" ++ sep ++ "zig" ++ EXE,
"c++",
"-target",
"x86_64-linux-gnu.2.28",
"main.c",
"-o",
"/dev/null",
},
.env_zig_lib_dir = "external" ++ sep ++ "zig_sdk" ++
sep ++ "lib",
},
},
},
};
for (tests) |tt| {
var tmp = testing.tmpDir(.{});
defer tmp.cleanup();
if (tt.precreate_dir) |dir|
try tmp.dir.makePath(dir);
var res = try parseArgs(allocator, tmp.dir, &TestArgIterator{
.argv = tt.args,
});
switch (tt.want_result) {
.err => |want_msg| try testing.expectEqualStrings(
want_msg,
res.err,
),
.exec => |want| {
try compareExec(res, want.args, want.env_zig_lib_dir);
},
}
}
}