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, 50 insertions, 34 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index b01b4bbae4..cbb44c1e18 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -2093,39 +2093,15 @@ pub fn update(comp: *Compilation) !void {
     }
 
     if (comp.totalErrorCount() != 0) {
-        // Skip flushing.
+        // Skip flushing and keep source files loaded for error reporting.
         comp.link_error_flags = .{};
         return;
     }
 
-    // This is needed before reading the error flags.
-    try comp.bin_file.flush(comp);
-    comp.link_error_flags = comp.bin_file.errorFlags();
-
-    if (!use_stage1) {
-        if (comp.bin_file.options.module) |module| {
-            try link.File.C.flushEmitH(module);
-        }
-    }
-
     // Flush takes care of -femit-bin, but we still have -femit-llvm-ir, -femit-llvm-bc, and
     // -femit-asm to handle, in the case of C objects.
     comp.emitOthers();
 
-    // If there are any errors, we anticipate the source files being loaded
-    // to report error messages. Otherwise we unload all source files to save memory.
-    // The ZIR needs to stay loaded in memory because (1) Decl objects contain references
-    // to it, and (2) generic instantiations, comptime calls, inline calls will need
-    // to reference the ZIR.
-    if (!comp.keep_source_files_loaded) {
-        if (comp.bin_file.options.module) |module| {
-            for (module.import_table.values()) |file| {
-                file.unloadTree(comp.gpa);
-                file.unloadSource(comp.gpa);
-            }
-        }
-    }
-
     if (comp.whole_cache_manifest != null) {
         const digest = man.final();
 
@@ -2139,23 +2115,63 @@ pub fn update(comp: *Compilation) !void {
         const o_sub_path = try std.fs.path.join(comp.gpa, &[_][]const u8{ "o", &digest });
         defer comp.gpa.free(o_sub_path);
 
-        try std.fs.rename(
-            comp.local_cache_directory.handle,
-            tmp_dir_sub_path,
-            comp.local_cache_directory.handle,
-            o_sub_path,
-        );
+        try comp.bin_file.renameTmpIntoCache(comp.local_cache_directory, tmp_dir_sub_path, o_sub_path);
+        comp.wholeCacheModeSetBinFilePath(&digest);
+
+        // This is intentionally sandwiched between renameTmpIntoCache() and writeManifest().
+        if (comp.bin_file.options.module) |module| {
+            // We need to set the zig_cache_artifact_directory for -femit-asm, -femit-llvm-ir,
+            // etc to know where to output to.
+            var artifact_dir = try comp.local_cache_directory.handle.openDir(o_sub_path, .{});
+            defer artifact_dir.close();
+
+            var dir_path = try comp.local_cache_directory.join(comp.gpa, &.{o_sub_path});
+            defer comp.gpa.free(dir_path);
+
+            module.zig_cache_artifact_directory = .{
+                .handle = artifact_dir,
+                .path = dir_path,
+            };
+
+            try comp.flush();
+        } else {
+            try comp.flush();
+        }
 
         // Failure here only means an unnecessary cache miss.
         man.writeManifest() catch |err| {
             log.warn("failed to write cache manifest: {s}", .{@errorName(err)});
         };
 
-        comp.wholeCacheModeSetBinFilePath(&digest);
-
         assert(comp.bin_file.lock == null);
         comp.bin_file.lock = man.toOwnedLock();
-        return;
+    } else {
+        try comp.flush();
+    }
+
+    // Unload all source files to save memory.
+    // The ZIR needs to stay loaded in memory because (1) Decl objects contain references
+    // to it, and (2) generic instantiations, comptime calls, inline calls will need
+    // to reference the ZIR.
+    if (!comp.keep_source_files_loaded) {
+        if (comp.bin_file.options.module) |module| {
+            for (module.import_table.values()) |file| {
+                file.unloadTree(comp.gpa);
+                file.unloadSource(comp.gpa);
+            }
+        }
+    }
+}
+
+fn flush(comp: *Compilation) !void {
+    try comp.bin_file.flush(comp); // This is needed before reading the error flags.
+    comp.link_error_flags = comp.bin_file.errorFlags();
+
+    const use_stage1 = build_options.is_stage1 and comp.bin_file.options.use_stage1;
+    if (!use_stage1) {
+        if (comp.bin_file.options.module) |module| {
+            try link.File.C.flushEmitH(module);
+        }
     }
 }