Add a script to generate stdlib GN rules from the Rust src tree

The tools/gnrt_stdlib.py script needs to be run when rolling Rust
in order to generate updated BUILD.gn files whenever the Cargo.toml
files change in the stdlib.

Previously gnrt gen --for-std would generate rules from the Rust
library found in //third_party/rust-toolchain, but that requires
Rust to already be rolled, so this now uses the feature of specifying
the Rust source tree root to --for-std.

Bug: 1401042
Change-Id: Id7c9e9c67687ad53fd5e4e5b469f7c2c18163a1b
Cq-Include-Trybots: luci.chromium.try:android-rust-arm32-rel,android-rust-arm64-rel,android-rust-arm64-dbg,linux-rust-x64-dbg,linux-rust-x64-rel,mac-rust-x64-dbg,win-rust-x64-dbg,win-rust-x64-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4600126
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1155567}

tools/clang/scripts/upload_revision.py

@@ -10,11 +10,9 @@ a CL, triggers Clang Upload try bots, and tells what to do next"""
 from __future__ import print_function
 
 import argparse
-import fnmatch
 import itertools
 import os
 import re
-import shutil
 import subprocess
 import sys
 import urllib.request
@@ -303,7 +301,9 @@ def main():
     print('Cannot set both --skip-clang and --skip-rust.')
     sys.exit(1)
 
-  if not args.skip_clang:
+  if args.skip_clang:
+    clang_version = '-skipped-'
+  else:
     if args.clang_git_hash:
       clang_git_hash = args.clang_git_hash
     else:
@@ -315,10 +315,10 @@ def main():
     clang_version = ClangVersion(GetCommitDescription(clang_git_hash),
                                  args.clang_sub_revision)
     os.chdir(CHROMIUM_DIR)
-  else:
-    clang_version = '-skipped-'
 
-  if not args.skip_rust:
+  if args.skip_rust:
+    rust_version = '-skipped-'
+  else:
     if args.rust_git_hash:
       rust_git_hash = args.rust_git_hash
     else:
@@ -326,8 +326,6 @@ def main():
     CheckoutGitRepo("Rust", RUST_GIT_URL, rust_git_hash, RUST_SRC_DIR)
     rust_version = RustVersion(rust_git_hash, args.rust_sub_revision)
     os.chdir(CHROMIUM_DIR)
-  else:
-    rust_version = '-skipped-'
 
   print(f'Making a patch for Clang {clang_version} and Rust {rust_version}')
 
@@ -420,6 +418,12 @@ def main():
 
   print('Please, wait until the try bots succeeded '
         'and then push the binaries to goma.')
+  print()
+  print('To regenerate BUILD.gn rules for Rust stdlib (needed if dep versions '
+        'in the stdlib change for example), run:\n  tools/rust/gnrt_stdlib.py.')
+  print()
+  print('To update Abseil .def files, run:\n  '
+        'third_party/abseil-cpp/generate_def_files.py')
 
 
 if __name__ == '__main__':

tools/crates/gnrt/gen.rs

@@ -106,6 +106,9 @@ fn generate_for_third_party(args: &clap::ArgMatches, paths: &paths::ChromiumPath
     if let Some(cargo_path) = args.get_one::<String>("cargo-path") {
         command.cargo_path(cargo_path);
     }
+    if let Some(rustc_path) = args.get_one::<String>("rustc-path") {
+        command.env("RUSTC", rustc_path);
+    }
 
     command.current_dir(&paths.third_party);
     let dependencies = deps::collect_dependencies(&command.exec().unwrap(), None, None);
@@ -261,6 +264,9 @@ fn generate_for_std(args: &clap::ArgMatches, paths: &paths::ChromiumPaths) -> Re
     if let Some(cargo_path) = args.get_one::<String>("cargo-path") {
         command.cargo_path(cargo_path);
     }
+    if let Some(rustc_path) = args.get_one::<String>("rustc-path") {
+        command.env("RUSTC", rustc_path);
+    }
 
     command.current_dir(paths.std_fake_root);
 

tools/crates/gnrt/lib/paths.rs

@@ -37,8 +37,13 @@ impl ChromiumPaths {
         Ok(ChromiumPaths {
             root: cur_dir.clone(),
             third_party: check_path(&cur_dir, RUST_THIRD_PARTY_DIR)?,
+            // We tolerate the Rust sources being missing, as they are only used to generate
+            // rules for the stdlib during Clang/Rust rolls, and they are not checked out for
+            // most machines.
             rust_src_vendor_subdir: Path::new(RUST_SRC_VENDOR_SUBDIR),
-            rust_src_installed: check_path(&cur_dir, RUST_SRC_INSTALLED_DIR)?,
+            // We tolerate the toolchain package dir being missing, as it's not checked out
+            // on the bots that generate Clang/Rust rolls.
+            rust_src_installed: Path::new(RUST_SRC_INSTALLED_DIR),
             std_config_file: check_path(&cur_dir, STD_CONFIG_FILE)?,
             std_build: check_path(&cur_dir, STD_BUILD_DIR)?,
             std_fake_root: check_path(&cur_dir, STD_FAKE_ROOT)?,

tools/crates/gnrt/main.rs

@@ -36,6 +36,14 @@ fn main() -> Result<()> {
                         .num_args(1)
                         .help("Path to the cargo executable"),
                 )
+                .arg(
+                    Arg::new("rustc-path")
+                        .long("rustc-path")
+                        .value_name("RUSTC_PATH")
+                        .value_parser(clap::value_parser!(String))
+                        .num_args(1)
+                        .help("Path to the rustc executable"),
+                )
                 .arg(
                     Arg::new("for-std")
                         .long("for-std")

tools/rust/gnrt_stdlib.py

@@ -58,7 +58,7 @@ def main():
         RunCommand([
             os.path.join(cargo_work_dir, 'release', f'gnrt{EXE}'), 'gen',
             f'--for-std={os.path.relpath(args.rust_src_dir, CHROMIUM_DIR)}',
-            f'--cargo-path={cargo_bin}'
+            f'--cargo-path={cargo_bin}', f'--rustc-path={rustc_bin}'
         ])