cmd/compile: add script testing facility for compiler use

Add support for running script tests as part of the compiler's suite
of tests, hooking in the script test engine packages recently moved
from cmd/go to cmd/internal. These script tests will use the test
binary itself as the compile tool for Go builds, and can also run the
C compiler if needed. New script test cases (*.txt files) should be
added to the directory cmd/compile/testdata/script.

Updates #68606.

Change-Id: I9b056a07024b0a72320a89ad734e4b4a51f1c10c
Reviewed-on: https://go-review.googlesource.com/c/go/+/601361
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/script_test.go

@@ -0,0 +1,62 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"cmd/internal/script/scripttest"
+	"internal/testenv"
+	"os"
+	"runtime"
+	"testing"
+)
+
+var testCompiler string
+
+// TestMain allows this test binary to run as the compiler
+// itself, which is helpful for running script tests.
+// If COMPILE_TEST_EXEC_COMPILE is set, we treat the run
+// as a 'go tool compile' invocation, otherwise behave
+// as a normal test binary.
+func TestMain(m *testing.M) {
+	// Are we being asked to run as the compiler?
+	// If so then kick off main.
+	if os.Getenv("COMPILE_TEST_EXEC_COMPILE") != "" {
+		main()
+		os.Exit(0)
+	}
+
+	if testExe, err := os.Executable(); err == nil {
+		// on wasm, some phones, we expect an error from os.Executable()
+		testCompiler = testExe
+	}
+
+	// Regular run, just execute tests.
+	os.Exit(m.Run())
+}
+
+func TestScript(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	doReplacement := true
+	switch runtime.GOOS {
+	case "wasip1", "js":
+		// wasm doesn't support os.Executable, so we'll skip replacing
+		// the installed linker with our test binary.
+		doReplacement = false
+	}
+	repls := []scripttest.ToolReplacement{}
+	if doReplacement {
+		if testCompiler == "" {
+			t.Fatalf("testCompiler not set, can't replace")
+		}
+		repls = []scripttest.ToolReplacement{
+			scripttest.ToolReplacement{
+				ToolName:        "compile",
+				ReplacementPath: testCompiler,
+				EnvVar:          "COMPILE_TEST_EXEC_COMPILE=1",
+			},
+		}
+	}
+	scripttest.RunToolScriptTest(t, repls, "testdata/script/*.txt")
+}

src/cmd/compile/testdata/script/script_test_basics.txt

@@ -0,0 +1,24 @@
+
+# Test of the linker's script test harness.
+
+go build
+[!cgo] skip
+cc -c testdata/mumble.c
+
+-- go.mod --
+module main
+
+go 1.20
+
+-- main.go --
+package main
+
+func main() {
+  println("Hi mom!")
+}
+
+-- testdata/mumble.c --
+
+int x;
+
+