Port //toolchain/install to new filesystem library (#5905)

This removes a bunch of manual filesystem helpers and complexity that
are directly provided by the new library.

It also moves all of the install paths detection to use
`std::filesystem::path` instead of the LLVM path library. The goal is to
consolidate all our logic onto a single stack, and the standard one
seems the best for that purpose. This does give up some of the
optimizations of this code to avoid memory allocation, but in practice
that likely isn't a critical issue. And with the new filesystem library
we can likely do more to avoid that by using directory-object-relative
filesystem access. However, that will have to wait for moving more parts
of the toolchain over to use this set of filesystem abstractions. There
is a related TODO left in the manifest handling code.

Author: chandlerc

toolchain/driver/clang_runner_test.cpp

@@ -55,7 +55,7 @@ TEST(ClangRunnerTest, Version) {
   EXPECT_THAT(out, HasSubstr((llvm::Twine("Target: ") + target).str()));
   // Clang's install should be our private LLVM install bin directory.
   EXPECT_THAT(out, HasSubstr(std::string("InstalledDir: ") +
-                             install_paths.llvm_install_bin()));
+                             install_paths.llvm_install_bin().native()));
 }
 
 // It's hard to write a portable and reliable unittest for all the layers of the

toolchain/install/BUILD

@@ -31,6 +31,7 @@ cc_library(
     deps = [
         "//common:check",
         "//common:error",
+        "//common:filesystem",
         "//toolchain/base:llvm_tools",
         "@bazel_tools//tools/cpp/runfiles",
         "@llvm-project//llvm:Support",
@@ -55,6 +56,8 @@ cc_test(
     deps = [
         ":install_paths",
         "//common:check",
+        "//common:error_test_helpers",
+        "//common:filesystem",
         "//common:ostream",
         "//testing/base:global_exe_path",
         "//testing/base:gtest_main",
@@ -83,6 +86,7 @@ cc_library(
     deps = [
         "//common:error",
         "//common:exe_path",
+        "//common:filesystem",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -94,6 +98,7 @@ cc_test(
     deps = [
         ":busybox_info",
         "//common:check",
+        "//common:filesystem",
         "//testing/base:gtest_main",
         "@googletest//:gtest",
         "@llvm-project//llvm:Support",

toolchain/install/busybox_info.cpp

@@ -7,6 +7,7 @@
 #include <iterator>
 
 #include "common/exe_path.h"
+#include "common/filesystem.h"
 #include "llvm/ADT/StringRef.h"
 
 namespace Carbon {
@@ -46,7 +47,8 @@ auto GetBusyboxInfo(const char* argv0) -> ErrorOr<BusyboxInfo> {
       // handled in the other return path.
       std::string prefix_root = info.bin_path.parent_path().string() +
                                 "/prefix_root/lib/carbon/carbon-busybox";
-      if (std::filesystem::exists(prefix_root)) {
+      if (auto access = Filesystem::Cwd().Access(prefix_root);
+          access.ok() && *access) {
         info.bin_path = prefix_root;
       }
       return info;
@@ -75,24 +77,23 @@ auto GetBusyboxInfo(const char* argv0) -> ErrorOr<BusyboxInfo> {
                           ? parent_path / ".." / "lib" / "carbon"
                           : parent_path / ".." / "..";
       auto busybox_path = lib_path / "carbon-busybox";
-      std::error_code ec;
-      if (std::filesystem::exists(busybox_path, ec)) {
+      if (auto access = Filesystem::Cwd().Access(busybox_path);
+          access.ok() && *access) {
         info.bin_path = busybox_path;
         return info;
       }
     }
 
     // Try to walk through another layer of symlinks and see if we can find the
     // installation there or are linked directly to the busybox.
-    std::error_code ec;
-    auto symlink_target = std::filesystem::read_symlink(info.bin_path, ec);
-    if (ec) {
+    auto readlink = Filesystem::Cwd().Readlink(info.bin_path);
+    if (!readlink.ok()) {
       return ErrorBuilder()
              << "expected carbon-busybox symlink at `" << info.bin_path << "`";
     }
 
     // Do a path join, to handle relative symlinks.
-    info.bin_path = parent_path / symlink_target;
+    info.bin_path = parent_path / *readlink;
   }
 }