misc/cgo/fortran: convert to Go test

Currently, the entry-point to this test is a Bash script that smoke
tests the FORTRAN compiler and then runs a FORTRAN-containing Go test.
This CL rearranges things so a pure Go Go test smoke tests the FORTRAN
compiler and then runs a non-test FORTRAN-containing Go binary.

While we're here, we fix a discrepancy when the host is GOARCH=amd64,
but the target is GOARCH=386. Previously, we would pick the wrong
libgfortran path because we didn't account for the cross-compilation,
causing the link to fail. Except for some reason this was ignored and
the test nevertheless "passed". In the new test we're a little more
strict, so this build failure will cause the test to fail, so we add a
little logic to account for cross-compilation with the host toolchain.

For #37486.

Change-Id: Ie6f70066885d6fbb4e1b5a2b1e13b85dee5b359b
Reviewed-on: https://go-review.googlesource.com/c/go/+/443069
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Austin Clements <austin@google.com>

misc/cgo/fortran/fortran_test.go

@@ -1,13 +1,81 @@
-// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2022 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 fortran
 
-import "testing"
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
 
 func TestFortran(t *testing.T) {
-	if a := TheAnswer(); a != 42 {
-		t.Errorf("Unexpected result for The Answer. Got: %d Want: 42", a)
+	// Find the FORTRAN compiler.
+	fc := os.Getenv("FC")
+	if fc == "" {
+		fc, _ = exec.LookPath("gfortran")
+	}
+	if fc == "" {
+		t.Skip("fortran compiler not found (try setting $FC)")
+	}
+
+	var fcExtra []string
+	if strings.Contains(fc, "gfortran") {
+		// TODO: This duplicates but also diverges from logic from cmd/go
+		// itself. For example, cmd/go merely adds -lgfortran without the extra
+		// library path work. If this is what's necessary to run gfortran, we
+		// should reconcile the logic here and in cmd/go.. Maybe this should
+		// become a cmd/go script test to share that logic.
+
+		// Add -m32 if we're targeting 386, in case this is a cross-compile.
+		if runtime.GOARCH == "386" {
+			fcExtra = append(fcExtra, "-m32")
+		}
+
+		// Find libgfortran. If the FORTRAN compiler isn't bundled
+		// with the C linker, this may be in a path the C linker can't
+		// find on its own. (See #14544)
+		libExt := "so"
+		switch runtime.GOOS {
+		case "darwin":
+			libExt = "dylib"
+		case "aix":
+			libExt = "a"
+		}
+		libPath, err := exec.Command(fc, append([]string{"-print-file-name=libgfortran." + libExt}, fcExtra...)...).CombinedOutput()
+		if err != nil {
+			t.Errorf("error invoking %s: %s", fc, err)
+		}
+		libDir := filepath.Dir(string(libPath))
+		cgoLDFlags := os.Getenv("CGO_LDFLAGS")
+		cgoLDFlags += " -L " + libDir
+		if runtime.GOOS != "aix" {
+			cgoLDFlags += " -Wl,-rpath," + libDir
+		}
+		t.Logf("CGO_LDFLAGS=%s", cgoLDFlags)
+		os.Setenv("CGO_LDFLAGS", cgoLDFlags)
+
+	}
+
+	// Do a test build that doesn't involve Go FORTRAN support.
+	fcArgs := append([]string{"helloworld/helloworld.f90", "-o", "/dev/null"}, fcExtra...)
+	t.Logf("%s %s", fc, fcArgs)
+	if err := exec.Command(fc, fcArgs...).Run(); err != nil {
+		t.Skipf("skipping Fortran test: could not build helloworld.f90 with %s: %s", fc, err)
+	}
+
+	// Finally, run the actual test.
+	t.Log("go", "run", "./testdata/testprog")
+	out, err := exec.Command("go", "run", "./testdata/testprog").CombinedOutput()
+	if err == nil && string(out) != "ok\n" {
+		err = fmt.Errorf("expected ok")
+	}
+	if err != nil {
+		t.Errorf("%s\nOutput:\n%s", err, string(out))
 	}
 }

misc/cgo/fortran/fortran.go → misc/cgo/fortran/testdata/testprog/fortran.go

@@ -2,11 +2,20 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package fortran
+package main
 
 // int the_answer();
 import "C"
+import "os"
 
 func TheAnswer() int {
 	return int(C.the_answer())
 }
+
+func main() {
+	if a := TheAnswer(); a != 42 {
+		println("Unexpected result for The Answer. Got:", a, " Want: 42")
+		os.Exit(1)
+	}
+	println("ok")
+}

src/cmd/dist/test.go

@@ -746,19 +746,8 @@ func (t *tester) registerTests() {
 		// Disabled on iOS. golang.org/issue/15919
 		t.registerHostTest("cgo_stdio", "../misc/cgo/stdio", "misc/cgo/stdio", ".")
 		t.registerHostTest("cgo_life", "../misc/cgo/life", "misc/cgo/life", ".")
-		fortran := os.Getenv("FC")
-		if fortran == "" {
-			fortran, _ = exec.LookPath("gfortran")
-		}
-		if t.hasBash() && goos != "android" && fortran != "" {
-			t.tests = append(t.tests, distTest{
-				name:    "cgo_fortran",
-				heading: "../misc/cgo/fortran",
-				fn: func(dt *distTest) error {
-					t.addCmd(dt, "misc/cgo/fortran", "./test.bash", fortran)
-					return nil
-				},
-			})
+		if goos != "android" {
+			t.registerHostTest("cgo_fortran", "../misc/cgo/fortran", "misc/cgo/fortran", ".")
 		}
 		if t.hasSwig() && goos != "android" {
 			t.tests = append(t.tests, distTest{