Improve Cache Unavailable error message due to file permissions issue

[jeffective]

Zig Version

0.14.0-dev.66+1fdf13a14

Steps to Reproduce and Observed Output

run zig build test

modify a file to trigger cache miss

run sudo /path/to/zig/executable build test

modify a file to trigger cache miss

run zig build test

observe cache unavailable error

test
└─ run test
   └─ zig test Debug native failure
error: error: CacheUnavailable

Remedy the situation by deleting the .zig-cache/ directory

Context: I was writing a quick test to test some interactions with network interfaces which required elevated privileges. I realize that it is a poor test design if it requires elevated privileges.

Expected Output

Perhaps this could report a file permissions error instead?

[WillLillis]

Adding the following line leads to an AccessDenied error rather than CacheUnavailable for this situation. I'm happy to open up a PR, but I'm not certain where/ how a test could be written to cover this behavior.

diff --git a/lib/std/Build/Cache.zig b/lib/std/Build/Cache.zig
index fe2a6b0a83..172f3dfd8e 100644
--- a/lib/std/Build/Cache.zig
+++ b/lib/std/Build/Cache.zig
@@ -568,6 +568,7 @@ pub const Manifest = struct {
                         if (try self.upgradeToExclusiveLock()) continue;
                         return false;
                     },
+                    error.AccessDenied => return error.AccessDenied,
                     else => return error.CacheUnavailable,
                 };
                 defer this_file.close();