avoid cross-package references in tests (google#385)

The previous implementation of DataFile (which abstracts different build systems' ways of locating test data files) constructed file names of data files using $GOPATH; also, it used a cross-package reference to locate the assert.star file. This doesn't work under Go modules. Now, DataFile looks only in the current directory, and the assert.star file is moved into a constant section of the executable.

Also, fix tests historically broken on Mac/Windows due to diff and CR LF differences.

internal/chunkedfile/chunkedfile.go

@@ -28,6 +28,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
 )
@@ -61,7 +62,13 @@ func Read(filename string, report Reporter) (chunks []Chunk) {
 		return
 	}
 	linenum := 1
-	for i, chunk := range strings.Split(string(data), "\n---\n") {
+
+	eol := "\n"
+	if runtime.GOOS == "windows" {
+		eol = "\r\n"
+	}
+
+	for i, chunk := range strings.Split(string(data), eol+"---"+eol) {
 		if debug {
 			fmt.Printf("chunk %d at line %d: %s\n", i, linenum, chunk)
 		}

internal/test.sh

@@ -10,8 +10,9 @@ set -eu
 cp go.mod go.mod.orig
 cp go.sum go.sum.orig
 go mod tidy
-diff go.mod.orig go.mod
-diff go.sum.orig go.sum
+# Use -w to ignore differences in OS newlines.
+diff -w  go.mod.orig go.mod
+diff -w go.sum.orig go.sum
 rm go.mod.orig go.sum.orig
 
 # Run tests

starlarktest/assert.star → starlarktest/assert.go

@@ -1,3 +1,9 @@
+package starlarktest
+
+// assertStar contains the logical data file assert.star.
+// TODO(adonovan): move it back into an actual file,
+// when fs.Embed is more than two releases old.
+const assertStar = `
 # Predeclared built-ins for this module:
 #
 # error(msg): report an error in Go's test framework without halting execution.
@@ -49,3 +55,4 @@ assert = module(
     contains = _contains,
     fails = _fails,
 )
+`

starlarktest/starlarktest.go

@@ -14,7 +14,6 @@ package starlarktest // import "go.starlark.net/starlarktest"
 
 import (
 	"fmt"
-	"go/build"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -68,12 +67,9 @@ func LoadAssertModule() (starlark.StringDict, error) {
 			"_freeze": starlark.NewBuiltin("freeze", freeze),
 		}
 		// TODO(adonovan): embed the file using embed.FS when we can rely on go1.16,
-		// and stop using DataFile. Otherwise this reaches from the application's working
-		// directory into the starlarktest package's directory, which is not compatible
-		// with modules.
-		filename := DataFile("starlarktest", "assert.star")
+		// and make the apparent filename reference that file.
 		thread := new(starlark.Thread)
-		assert, assertErr = starlark.ExecFile(thread, filename, nil, predeclared)
+		assert, assertErr = starlark.ExecFile(thread, "builtins/assert.star", assertStar, predeclared)
 	})
 	return assert, assertErr
 }
@@ -147,5 +143,7 @@ var DataFile = func(pkgdir, filename string) string {
 		return filepath.Join(testSrcdir, "net_starlark_go", pkgdir, filename)
 	}
 
-	return filepath.Join(build.Default.GOPATH, "src/go.starlark.net", pkgdir, filename)
+	// Under go test, ignore pkgdir, which is the directory of the
+	// current package relative to the module root.
+	return filename
 }