[llvm] [Support] Better error msg when cache dir can't be created. (PR #69575)

[Tobias Hieta via llvm-commits]

https://github.com/tru created https://github.com/llvm/llvm-project/pull/69575

On windows if you passed /lldltocache:D:\tmp to lld and you didn't have D: mounted it fail to create the cache dir D:\tmp, but the error message is pretty hard to understand:

```
c:\code\llvm\llvm-project\out\debug>bin\lld-link.exe /lldltocache:D:\tmp
hello.obj
LLVM ERROR: no such file or directory

PLEASE submit a bug report to
https://github.com/llvm/llvm-project/issues/ and include the crash
backtrace.
Exception Code: 0xC000001D
```

Which lead one of our users to report this as a crash. I have just added a bit better message so it now says:

```
c:\code\llvm\llvm-project\out\debug>bin\lld-link.exe /lldltocache:D:\tmp
hello.obj
LLVM ERROR: Can't create cache directory: D:\tmp

PLEASE submit a bug report to
https://github.com/llvm/llvm-project/issues/ and include the crash
backtrace.
```

I am not sure this is a fatal error because it's not something that really should be reported as a bug to LLVM. But at least this gives a bit more visibility on what to change.

>From c66936964c514b12e97be747d7f4384278cfd260 Mon Sep 17 00:00:00 2001
From: Tobias Hieta <tobias.hieta at ubisoft.com>
Date: Thu, 19 Oct 2023 11:10:35 +0200
Subject: [PATCH] [Support] Better error msg when cache dir can't be created.

On windows if you passed /lldltocache:D:\tmp to lld and you didn't have
D: mounted it fail to create the cache dir D:\tmp, but the error message
is pretty hard to understand:

```
c:\code\llvm\llvm-project\out\debug>bin\lld-link.exe /lldltocache:D:\tmp
hello.obj
LLVM ERROR: no such file or directory

PLEASE submit a bug report to
https://github.com/llvm/llvm-project/issues/ and include the crash
backtrace.
Exception Code: 0xC000001D
```

Which lead one of our users to report this as a crash. I have just added
a bit better message so it now says:

```
c:\code\llvm\llvm-project\out\debug>bin\lld-link.exe /lldltocache:D:\tmp
hello.obj
LLVM ERROR: Can't create cache directory: D:\tmp

PLEASE submit a bug report to
https://github.com/llvm/llvm-project/issues/ and include the crash
backtrace.
```

I am not sure this is a fatal error because it's not something that
really should be reported as a bug to LLVM. But at least this gives a
bit more visibility on what to change.
---
 llvm/lib/Support/Caching.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/Support/Caching.cpp b/llvm/lib/Support/Caching.cpp
index f20f08a865c76ff..722746e7b440390 100644
--- a/llvm/lib/Support/Caching.cpp
+++ b/llvm/lib/Support/Caching.cpp
@@ -145,7 +145,7 @@ Expected<FileCache> llvm::localCache(const Twine &CacheNameRef,
       // ensures the filesystem isn't mutated until the cache is.
       if (std::error_code EC = sys::fs::create_directories(
               CacheDirectoryPath, /*IgnoreExisting=*/true))
-        return errorCodeToError(EC);
+        return createStringError(EC, Twine("Can't create cache directory: ") + CacheDirectoryPath);
 
       // Write to a temporary to avoid race condition
       SmallString<64> TempFilenameModel;