Restore basic functionality of the C++ process wrapper

rust/private/rust.bzl

@@ -1094,12 +1094,12 @@ rust_binary = rule(
 """),
 )
 
-def _common_attrs_for_binary_without_process_wrapper(attrs):
+def _common_attrs_for_binary_with_basic_process_wrapper(attrs):
     new_attr = dict(attrs)
 
     # use a fake process wrapper
     new_attr["_process_wrapper"] = attr.label(
-        default = None,
+        default = "//util/process_wrapper:basic_process_wrapper",
         executable = True,
         allow_single_file = True,
         cfg = "exec",
@@ -1108,7 +1108,7 @@ def _common_attrs_for_binary_without_process_wrapper(attrs):
     # fix stamp = 0
     new_attr["stamp"] = attr.int(
         doc = dedent("""\
-            Fix `stamp = 0` as stamping is not supported when building without process_wrapper:
+            Fix `stamp = 0` as stamping is not supported when building with the basic process_wrapper:
             https://github.com/bazelbuild/rules_rust/blob/8df4517d370b0c543a01ba38b63e1d5a4104b035/rust/private/rustc.bzl#L955
         """),
         default = 0,
@@ -1120,10 +1120,10 @@ def _common_attrs_for_binary_without_process_wrapper(attrs):
 # Provides an internal rust_{binary,library} to use that we can use to build the process
 # wrapper, this breaks the dependency of rust_* on the process wrapper by
 # setting it to None, which the functions in rustc detect and build accordingly.
-rust_binary_without_process_wrapper = rule(
+rust_binary_with_basic_process_wrapper = rule(
     implementation = _rust_binary_impl,
     provides = _common_providers,
-    attrs = _common_attrs_for_binary_without_process_wrapper(_common_attrs.items() + _rust_binary_attrs.items()),
+    attrs = _common_attrs_for_binary_with_basic_process_wrapper(_common_attrs.items() + _rust_binary_attrs.items()),
     executable = True,
     fragments = ["cpp"],
     host_fragments = ["cpp"],
@@ -1134,10 +1134,10 @@ rust_binary_without_process_wrapper = rule(
     incompatible_use_toolchain_transition = True,
 )
 
-rust_library_without_process_wrapper = rule(
+rust_library_with_basic_process_wrapper = rule(
     implementation = _rust_library_impl,
     provides = _common_providers,
-    attrs = dict(_common_attrs_for_binary_without_process_wrapper(_common_attrs).items()),
+    attrs = dict(_common_attrs_for_binary_with_basic_process_wrapper(_common_attrs).items()),
     fragments = ["cpp"],
     host_fragments = ["cpp"],
     toolchains = [

rust/private/rustc.bzl

@@ -35,6 +35,7 @@ load(
     "is_exec_configuration",
     "make_static_lib_symlink",
     "relativize",
+    "uses_process_wrapper",
 )
 
 BuildInfo = _BuildInfo
@@ -1207,7 +1208,7 @@ def rustc_compile_action(
             dsym_folder = ctx.actions.declare_directory(crate_info.output.basename + ".dSYM", sibling = crate_info.output)
             action_outputs.append(dsym_folder)
 
-    if ctx.executable._process_wrapper:
+    if uses_process_wrapper(ctx):
         # Run as normal
         ctx.actions.run(
             executable = ctx.executable._process_wrapper,
@@ -1239,17 +1240,17 @@ def rustc_compile_action(
                 ),
             )
     else:
-        # Run without process_wrapper
+        # Run with the basic process_wrapper
         if build_env_files or build_flags_files or stamp or build_metadata:
-            fail("build_env_files, build_flags_files, stamp, build_metadata are not supported when building without process_wrapper")
+            fail("build_env_files, build_flags_files, stamp, build_metadata are not supported when building with the basic process wrapper")
         ctx.actions.run(
-            executable = toolchain.rustc,
+            executable = ctx.executable._process_wrapper,
             inputs = compile_inputs,
             outputs = action_outputs,
             env = env,
-            arguments = [args.rustc_flags],
+            arguments = [toolchain.rustc.path, args.rustc_flags],
             mnemonic = "Rustc",
-            progress_message = "Compiling Rust (without process_wrapper) {} {}{} ({} files)".format(
+            progress_message = "Compiling Rust (for process wrapper) {} {}{} ({} files)".format(
                 crate_info.type,
                 ctx.label.name,
                 formatted_version,

rust/private/utils.bzl

@@ -680,7 +680,7 @@ def can_build_metadata(toolchain, ctx, crate_type):
     # 4) the crate_type is rlib or lib.
     return toolchain._pipelined_compilation and \
            toolchain.exec_triple.system != "windows" and \
-           ctx.attr._process_wrapper and \
+           uses_process_wrapper(ctx) and \
            crate_type in ("rlib", "lib")
 
 def crate_root_src(name, srcs, crate_type):
@@ -708,6 +708,18 @@ def crate_root_src(name, srcs, crate_type):
         fail("No {} source file found.".format(" or ".join(file_names)), "srcs")
     return crate_root
 
+def uses_process_wrapper(ctx):
+    """Returns true if this action uses the full fledged process wrapper.
+
+    Args:
+        ctx (list): The rule's context object
+
+    Returns:
+        bool: True if the full flaged process wrapper is used, false otherwise.
+    """
+
+    return "basic_process_wrapper" not in ctx.executable._process_wrapper.path
+
 def _shortest_src_with_basename(srcs, basename):
     """Finds the shortest among the paths in srcs that match the desired basename.
 

util/process_wrapper/BUILD.bazel

@@ -1,9 +1,10 @@
+load("@rules_cc//cc:defs.bzl", "cc_binary")
 load("//rust:defs.bzl", "rust_test")
 
 # buildifier: disable=bzl-visibility
-load("//rust/private:rust.bzl", "rust_binary_without_process_wrapper")
+load("//rust/private:rust.bzl", "rust_binary_with_basic_process_wrapper")
 
-rust_binary_without_process_wrapper(
+rust_binary_with_basic_process_wrapper(
     name = "process_wrapper",
     srcs = glob(["*.rs"]),
     edition = "2018",
@@ -18,3 +19,26 @@ rust_test(
     crate = ":process_wrapper",
     edition = "2018",
 )
+
+cc_binary(
+    name = "basic_process_wrapper",
+    srcs = [
+        "basic_process_wrapper.cc",
+        "system.h",
+    ] + select({
+        "@bazel_tools//src/conditions:host_windows": [
+            "system_windows.cc",
+        ],
+        "//conditions:default": [
+            "system_posix.cc",
+        ],
+    }),
+    defines = [] + select({
+        "@bazel_tools//src/conditions:host_windows": [
+            "UNICODE",
+            "_UNICODE",
+        ],
+        "//conditions:default": [],
+    }),
+    visibility = ["//visibility:public"],
+)

util/process_wrapper/BUILD.tinyjson.bazel

@@ -1,7 +1,7 @@
 # buildifier: disable=bzl-visibility
-load("@rules_rust//rust/private:rust.bzl", "rust_library_without_process_wrapper")
+load("@rules_rust//rust/private:rust.bzl", "rust_library_with_basic_process_wrapper")
 
-rust_library_without_process_wrapper(
+rust_library_with_basic_process_wrapper(
     name = "tinyjson",
     srcs = glob(["src/*.rs"]),
     edition = "2018",

util/process_wrapper/basic_process_wrapper.cc

@@ -0,0 +1,37 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <utility>
+
+#include "util/process_wrapper/system.h"
+
+using CharType = process_wrapper::System::StrType::value_type;
+
+// A basic process wrapper whose only purpose is to preserve determinism when
+// building the true process wrapper. We do this by passing --remap-path-prefix=$pwd=
+// to the command line.
+int PW_MAIN(int argc, const CharType* argv[], const CharType* envp[]) {
+  using namespace process_wrapper;
+
+  System::EnvironmentBlock environment_block;
+
+  // Taking all environment variables from the current process
+  // and sending them down to the child process
+  for (int i = 0; envp[i] != nullptr; ++i) {
+    environment_block.push_back(envp[i]);
+  }
+
+  System::StrType exec_path = argv[1];
+
+  System::Arguments arguments;
+
+  for (int i = 2; i < argc; ++i) {
+    arguments.push_back(argv[i]);
+  }
+  System::StrType pwd_prefix =
+      PW_SYS_STR("--remap-path-prefix=") + System::GetWorkingDirectory() + PW_SYS_STR("=");
+  arguments.push_back(pwd_prefix);
+
+  return System::Exec(exec_path, arguments, environment_block);
+}

util/process_wrapper/system.h

@@ -0,0 +1,47 @@
+#ifndef LIB_PROCESS_WRAPPER_SYSTEM_H_
+#define LIB_PROCESS_WRAPPER_SYSTEM_H_
+
+#include <string>
+#include <vector>
+
+#if defined(_WIN32) && defined(UNICODE)
+#define PW_WIN_UNICODE
+#endif  // defined(_WIN32) && defined(UNICODE)
+
+#if defined(PW_WIN_UNICODE)
+#define PW_SYS_STR(str) L##str
+#define PW_MAIN wmain
+#else
+#define PW_SYS_STR(str) str
+#define PW_MAIN main
+#endif
+
+namespace process_wrapper {
+
+class System {
+ public:
+#if defined(PW_WIN_UNICODE)
+  using StrType = std::wstring;
+#else
+  using StrType = std::string;
+#endif  // defined(PW_WIN_UNICODE)
+
+  using StrVecType = std::vector<StrType>;
+  using Arguments = StrVecType;
+  using EnvironmentBlock = StrVecType;
+
+ public:
+  // Gets the working directory of the current process
+  static StrType GetWorkingDirectory();
+
+  // Simple function to execute a process that inherits all the current
+  // process handles.
+  // Even if the function doesn't modify global state it is not reentrant
+  // It is meant to be called once during the lifetime of the parent process
+  static int Exec(const StrType& executable, const Arguments& arguments,
+                  const EnvironmentBlock& environment_block);
+};
+
+}  // namespace process_wrapper
+
+#endif  // LIB_PROCESS_WRAPPER_SYSTEM_H_

util/process_wrapper/system_posix.cc

@@ -0,0 +1,127 @@
+#include "util/process_wrapper/system.h"
+
+// posix headers
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <cerrno>
+#include <cstring>
+#include <iostream>
+#include <vector>
+
+namespace process_wrapper {
+
+namespace {
+
+class OutputPipe {
+ public:
+  static constexpr size_t kReadEndDesc = 0;
+  static constexpr size_t kWriteEndDesc = 1;
+
+  ~OutputPipe() {
+    CloseReadEnd();
+    CloseWriteEnd();
+  }
+
+  int CreateEnds() {
+    if (pipe(output_pipe_desc_) != 0) {
+      std::cerr << "process wrapper error: failed to open the stdout pipes.\n";
+      return false;
+    }
+    return true;
+  }
+  void DupWriteEnd(int newfd) {
+    dup2(output_pipe_desc_[kWriteEndDesc], newfd);
+    CloseReadEnd();
+    CloseWriteEnd();
+  }
+
+  void CloseReadEnd() { Close(kReadEndDesc); }
+  void CloseWriteEnd() { Close(kWriteEndDesc); }
+
+  int ReadEndDesc() const { return output_pipe_desc_[kReadEndDesc]; }
+  int WriteEndDesc() const { return output_pipe_desc_[kWriteEndDesc]; }
+
+ private:
+  void Close(size_t idx) {
+    if (output_pipe_desc_[idx] > 0) {
+      close(output_pipe_desc_[idx]);
+    }
+    output_pipe_desc_[idx] = -1;
+  }
+  int output_pipe_desc_[2] = {-1};
+};
+
+}  // namespace
+
+System::StrType System::GetWorkingDirectory() {
+  const size_t kMaxBufferLength = 4096;
+  char cwd[kMaxBufferLength];
+  if (getcwd(cwd, sizeof(cwd)) == NULL) {
+    return System::StrType{};
+  }
+  return System::StrType{cwd};
+}
+
+int System::Exec(const System::StrType &executable,
+                 const System::Arguments &arguments,
+                 const System::EnvironmentBlock &environment_block) {
+  OutputPipe stdout_pipe;
+  if (!stdout_pipe.CreateEnds()) {
+    return -1;
+  }
+  OutputPipe stderr_pipe;
+  if (!stderr_pipe.CreateEnds()) {
+    return -1;
+  }
+
+  pid_t child_pid = fork();
+  if (child_pid < 0) {
+    std::cerr << "process wrapper error: failed to fork the current process: "
+              << std::strerror(errno) << ".\n";
+    return -1;
+  } else if (child_pid == 0) {
+    std::vector<char *> argv;
+    argv.push_back(const_cast<char *>(executable.c_str()));
+    for (const StrType &argument : arguments) {
+      argv.push_back(const_cast<char *>(argument.c_str()));
+    }
+    argv.push_back(nullptr);
+
+    std::vector<char *> envp;
+    for (const StrType &ev : environment_block) {
+      envp.push_back(const_cast<char *>(ev.c_str()));
+    }
+    envp.push_back(nullptr);
+
+    umask(022);
+    execve(executable.c_str(), argv.data(), envp.data());
+    std::cerr << "process wrapper error: failed to exec the new process: "
+              << std::strerror(errno) << ".\n";
+    return -1;
+  }
+
+  int err, exit_status;
+  do {
+    err = waitpid(child_pid, &exit_status, 0);
+  } while (err == -1 && errno == EINTR);
+
+  if (WIFEXITED(exit_status)) {
+    return WEXITSTATUS(exit_status);
+  } else if (WIFSIGNALED(exit_status)) {
+    raise(WTERMSIG(exit_status));
+  } else if (WIFSTOPPED(exit_status)) {
+    raise(WSTOPSIG(exit_status));
+  } else {
+    std::cerr << "process wrapper error: failed to parse exit code of the "
+                 "child process: "
+              << exit_status << ".\n";
+  }
+  return -1;
+}
+
+}  // namespace process_wrapper