Fix all std lib tests being run for any file within the std package

Before this commit:

```
$ zig test lib/std/fs/test.zig --main-pkg-path lib/std --zig-lib-dir lib
2170 passed; 37 skipped; 0 failed.
```

After this commit:

```
$ zig test lib/std/fs/test.zig --main-pkg-path lib/std --zig-lib-dir lib
All 45 tests passed.
```

This matches stage1 behavior:

```
$ zig test -fstage1 lib/std/fs/test.zig --main-pkg-path lib/std --zig-lib-dir lib
All 45 tests passed.
```

All tests are still run if `zig test` is run directly on `lib/std/std.zig`:

```
$ zig test lib/std/std.zig --main-pkg-path lib/std --zig-lib-dir lib
2170 passed; 37 skipped; 0 failed.
```

`zig build test-std` is unaffected by this change.

Closes #12926

1 files changed, 4 insertions, 4 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 90f830384d..7c4c369a6b 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -1588,10 +1588,10 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             try main_pkg.add(gpa, "root", root_pkg);
             try main_pkg.addAndAdopt(gpa, "std", std_pkg);
 
-            const main_pkg_in_std = m: {
+            const main_pkg_is_std = m: {
                 const std_path = try std.fs.path.resolve(arena, &[_][]const u8{
                     std_pkg.root_src_directory.path orelse ".",
-                    std.fs.path.dirname(std_pkg.root_src_path) orelse ".",
+                    std_pkg.root_src_path,
                 });
                 defer arena.free(std_path);
                 const main_path = try std.fs.path.resolve(arena, &[_][]const u8{
@@ -1599,7 +1599,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
                     main_pkg.root_src_path,
                 });
                 defer arena.free(main_path);
-                break :m mem.startsWith(u8, main_path, std_path);
+                break :m mem.eql(u8, main_path, std_path);
             };
 
             // Pre-open the directory handles for cached ZIR code so that it does not need
@@ -1638,7 +1638,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
                 .gpa = gpa,
                 .comp = comp,
                 .main_pkg = main_pkg,
-                .main_pkg_in_std = main_pkg_in_std,
+                .main_pkg_is_std = main_pkg_is_std,
                 .root_pkg = root_pkg,
                 .zig_cache_artifact_directory = zig_cache_artifact_directory,
                 .global_zir_cache = global_zir_cache,