simplify zig0 test setup: single test module, remove zig0_test.zig

Consolidate the two separate test modules (test_mod via
lib/std/zig/zig0_test.zig + astgen_test_mod via stage0_test_root.zig)
into a single test module rooted at stage0_test_root.zig.

The zig0_test.zig bridge approach ran std's parser/tokenizer tests with
C comparison enabled, but the stage0/ test files already do the same
C-vs-Zig comparison directly via @cImport. The only "lost" tests are an
unnamed root test block and a Zig-only fuzz test — no zig0 coverage lost.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

build.zig

@@ -1606,65 +1606,43 @@ fn addZig0TestStep(
     valgrind: bool,
     test_timeout: ?[]const u8,
 ) void {
-    const bridge_mod = b.createModule(.{
-        .root_source_file = b.path("stage0/zig0_bridge.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-    bridge_mod.addIncludePath(b.path("stage0"));
-
-    // Parser + tokenizer tests (hooks into std's test files via zig0 bridge)
     const test_mod = b.createModule(.{
-        .root_source_file = b.path("lib/std/zig/zig0_test.zig"),
-        .optimize = optimize,
-        .target = target,
-    });
-    test_mod.addImport("zig0_bridge", bridge_mod);
-
-    // AstGen tests (standalone C-vs-Zig ZIR comparison)
-    const astgen_test_mod = b.createModule(.{
         .root_source_file = b.path("stage0_test_root.zig"),
         .optimize = optimize,
         .target = target,
     });
-    astgen_test_mod.addIncludePath(b.path("stage0"));
+    test_mod.addIncludePath(b.path("stage0"));
+    addZig0CSources(b, test_mod, cc, optimize);
+    test_mod.linkSystemLibrary("c", .{});
 
     const timeout: ?[]const u8 = test_timeout orelse if (valgrind) null else "10";
 
-    for ([_]struct { mod: *std.Build.Module, name: []const u8 }{
+    const test_exe = b.addTest(.{
-        .{ .mod = test_mod, .name = "test" },
+        .root_module = test_mod,
-        .{ .mod = astgen_test_mod, .name = "astgen_test" },
+        .use_llvm = false,
-    }) |entry| {
+        .use_lld = false,
-        addZig0CSources(b, entry.mod, cc, optimize);
+    });
-        entry.mod.linkSystemLibrary("c", .{});
+    if (valgrind) {
-
+        test_exe.setExecCmd(&.{
-        const test_exe = b.addTest(.{
+            "valgrind",
-            .root_module = entry.mod,
+            "--error-exitcode=2",
-            .use_llvm = false,
+            "--leak-check=full",
-            .use_lld = false,
+            "--show-leak-kinds=all",
+            "--errors-for-leak-kinds=all",
+            "--track-fds=yes",
+            "--quiet",
+            null,
         });
-        if (valgrind) {
+    } else {
-            test_exe.setExecCmd(&.{
+        test_exe.setExecCmd(&.{ "timeout", timeout orelse "10", null });
-                "valgrind",
+    }
-                "--error-exitcode=2",
+    if (no_exec) {
-                "--leak-check=full",
+        const install = b.addInstallArtifact(test_exe, .{});
-                "--show-leak-kinds=all",
+        step.dependOn(&install.step);
-                "--errors-for-leak-kinds=all",
+    } else {
-                "--track-fds=yes",
+        const run = b.addRunArtifact(test_exe);
-                "--quiet",
+        run.step.name = b.fmt("test ({s})", .{cc});
-                null,
+        step.dependOn(&run.step);
-            });
-        } else {
-            test_exe.setExecCmd(&.{ "timeout", timeout orelse "10", null });
-        }
-        if (no_exec) {
-            const install = b.addInstallArtifact(test_exe, .{});
-            step.dependOn(&install.step);
-        } else {
-            const run = b.addRunArtifact(test_exe);
-            run.step.name = b.fmt("{s} ({s})", .{ entry.name, cc });
-            step.dependOn(&run.step);
-        }
     }
 }
 

lib/std/zig/zig0_test.zig

@@ -1,6 +0,0 @@
-pub const zig0 = @import("zig0_bridge");
-
-test {
-    _ = @import("parser_test.zig");
-    _ = @import("tokenizer.zig");
-}

stage0_test_root.zig

@@ -1,3 +1,5 @@
 test {
+    _ = @import("stage0/tokenizer_test.zig");
+    _ = @import("stage0/parser_test.zig");
     _ = @import("stage0/astgen_test.zig");
 }