stage2: introduce renameTmpIntoCache into the linker API

Doc comments reproduced here:

This function is called by the frontend before flush(). It communicates that
`options.bin_file.emit` directory needs to be renamed from
`[zig-cache]/tmp/[random]` to `[zig-cache]/o/[digest]`.
The frontend would like to simply perform a file system rename, however,
some linker backends care about the file paths of the objects they are linking.
So this function call tells linker backends to rename the paths of object files
to observe the new directory path.
Linker backends which do not have this requirement can fall back to the simple
implementation at the bottom of this function.
This function is only called when CacheMode is `whole`.

This solves stack trace regressions on Windows and macOS because the
linker backends do not observe object file paths until flush().

1 files changed, 6 insertions, 4 deletions

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index a248fb1718..e29116476d 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -324,10 +324,12 @@ pub const Object = struct {
         const mod = comp.bin_file.options.module.?;
         const cache_dir = mod.zig_cache_artifact_directory;
 
-        const emit_bin_path: ?[*:0]const u8 = if (comp.bin_file.options.emit) |emit|
-            try emit.directory.joinZ(arena, &[_][]const u8{self.sub_path})
-        else
-            null;
+        const emit_bin_path: ?[*:0]const u8 = if (comp.bin_file.options.emit) |emit| blk: {
+            const full_out_path = try emit.directory.join(arena, &[_][]const u8{emit.sub_path});
+            break :blk try std.fs.path.joinZ(arena, &.{
+                std.fs.path.dirname(full_out_path).?, self.sub_path,
+            });
+        } else null;
 
         const emit_asm_path = try locPath(arena, comp.emit_asm, cache_dir);
         const emit_llvm_ir_path = try locPath(arena, comp.emit_llvm_ir, cache_dir);