[llvm][Support] Add and use errnoAsErrorCode (#84423)

LLVM is inconsistent about how it converts `errno` to `std::error_code`.
This can cause problems because values outside of `std::errc` compare
differently if one is system and one is generic on POSIX systems.

This is even more of a problem on Windows where use of the system
category is just wrong, as that is for Windows errors, which have a
completely different mapping than POSIX/generic errors. This patch fixes
one instance of this mistake in `JSONTransport.cpp`.

This patch adds `errnoAsErrorCode()` which makes it so people do not
need to think about this issue in the future. It also cleans up a lot of
usage of `errno` in LLVM and Clang.

1 files changed, 7 insertions, 12 deletions

diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index acee228..4db9bc8 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -23,7 +23,6 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include <cctype>
-#include <cerrno>
 
 #if !defined(_MSC_VER) && !defined(__MINGW32__)
 #include <unistd.h>
@@ -1010,7 +1009,7 @@ static std::error_code copy_file_internal(int ReadFD, int WriteFD) {
   delete[] Buf;
 
   if (BytesRead < 0 || BytesWritten < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
@@ -1060,7 +1059,7 @@ ErrorOr<MD5::MD5Result> md5_contents(int FD) {
   }
 
   if (BytesRead < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   MD5::MD5Result Result;
   Hash.final(Result);
   return Result;
@@ -1228,7 +1227,7 @@ TempFile::~TempFile() { assert(Done); }
 Error TempFile::discard() {
   Done = true;
   if (FD != -1 && close(FD) == -1) {
-    std::error_code EC = std::error_code(errno, std::generic_category());
+    std::error_code EC = errnoAsErrorCode();
     return errorCodeToError(EC);
   }
   FD = -1;
@@ -1297,10 +1296,8 @@ Error TempFile::keep(const Twine &Name) {
   if (!RenameEC)
     TmpName = "";
 
-  if (close(FD) == -1) {
-    std::error_code EC(errno, std::generic_category());
-    return errorCodeToError(EC);
-  }
+  if (close(FD) == -1)
+    return errorCodeToError(errnoAsErrorCode());
   FD = -1;
 
   return errorCodeToError(RenameEC);
@@ -1319,10 +1316,8 @@ Error TempFile::keep() {
 
   TmpName = "";
 
-  if (close(FD) == -1) {
-    std::error_code EC(errno, std::generic_category());
-    return errorCodeToError(EC);
-  }
+  if (close(FD) == -1)
+    return errorCodeToError(errnoAsErrorCode());
   FD = -1;
 
   return Error::success();