[tools] Move getProjectRoot() out to fileutils.

Add tests.
This is going to be used by intrinsic-gen, a new tool

Bug: tint:832
Change-Id: Ib22ffa88a699be9c8dfdf3f8f6e32cff4ffc88e3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/52602
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

tools/src/cmd/trim-includes/main.go

diff --git a/tools/src/cmd/trim-includes/main.go b/tools/src/cmd/trim-includes/main.go
index ce195d7..146a6fc 100644
--- a/tools/src/cmd/trim-includes/main.go
+++ b/tools/src/cmd/trim-includes/main.go
@@ -30,20 +30,15 @@
 	"os/exec"
 	"path/filepath"
 	"regexp"
-	"runtime"
 	"strings"
 	"sync"
 	"time"
 
+	"dawn.googlesource.com/tint/tools/src/fileutils"
 	"dawn.googlesource.com/tint/tools/src/glob"
 )
 
 var (
-	// Directory to this .go file
-	toolRoot = getToolRoot()
-	// Root directory of the Tint project
-	projectRoot = getProjectRoot(toolRoot)
-
 	// Path to the build script to run after each attempting to remove each
 	// #include
 	buildScript = ""
@@ -104,7 +99,7 @@
 	}
 
 	fmt.Println("Scanning for files...")
-	paths, err := glob.Scan(projectRoot, cfg)
+	paths, err := glob.Scan(fileutils.ProjectRoot(), cfg)
 	if err != nil {
 		return err
 	}
@@ -235,7 +230,7 @@
 
 // Runs git add on the file
 func (f *file) stage() error {
-	err := exec.Command("git", "-C", projectRoot, "add", f.path).Run()
+	err := exec.Command("git", "-C", fileutils.ProjectRoot(), "add", f.path).Run()
 	if err != nil {
 		return fmt.Errorf("Couldn't stage file '%v': %w", f.path, err)
 	}
@@ -250,7 +245,7 @@
 	files := make([]file, len(paths))
 	errs := make([]error, len(paths))
 	for i, path := range paths {
-		i, path := i, filepath.Join(projectRoot, path)
+		i, path := i, filepath.Join(fileutils.ProjectRoot(), path)
 		go func() {
 			defer wg.Done()
 			body, err := ioutil.ReadFile(path)
@@ -271,25 +266,3 @@
 	}
 	return files, nil
 }
-
-// Returns the path to the directory holding this .go file
-func getToolRoot() string {
-	_, filename, _, ok := runtime.Caller(0)
-	if !ok {
-		panic("No caller information")
-	}
-	mainPath, err := filepath.Abs(filename)
-	if err != nil {
-		panic(err)
-	}
-	return filepath.Dir(mainPath)
-}
-
-// Returns the path to the project root
-func getProjectRoot(toolRoot string) string {
-	root, err := filepath.Abs(filepath.Join(toolRoot, "../.."))
-	if err != nil {
-		panic(err)
-	}
-	return root
-}

tools/src/fileutils/fileutils.go

diff --git a/tools/src/fileutils/fileutils.go b/tools/src/fileutils/fileutils.go
index 7410086..8647193 100644
--- a/tools/src/fileutils/fileutils.go
+++ b/tools/src/fileutils/fileutils.go
@@ -17,6 +17,8 @@
 
 import (
 	"os"
+	"path/filepath"
+	"runtime"
 )
 
 // IsExe returns true if the file at path is an executable
@@ -27,3 +29,27 @@
 	}
 	return s.Mode()&0100 != 0
 }
+
+// GoSourcePath returns the absolute path to the .go file that calls the
+// function
+func GoSourcePath() string {
+	_, filename, _, ok := runtime.Caller(1)
+	if !ok {
+		panic("No caller information")
+	}
+	path, err := filepath.Abs(filename)
+	if err != nil {
+		panic(err)
+	}
+	return path
+}
+
+// ProjectRoot returns the path to the tint project root
+func ProjectRoot() string {
+	toolRoot := filepath.Dir(GoSourcePath())
+	root, err := filepath.Abs(filepath.Join(toolRoot, "../../.."))
+	if err != nil {
+		panic(err)
+	}
+	return root
+}

tools/src/fileutils/fileutils_test.go

diff --git a/tools/src/fileutils/fileutils_test.go b/tools/src/fileutils/fileutils_test.go
new file mode 100644
index 0000000..696353e
--- /dev/null
+++ b/tools/src/fileutils/fileutils_test.go
@@ -0,0 +1,38 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fileutils_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"dawn.googlesource.com/tint/tools/src/fileutils"
+)
+
+func TestGoSourcePath(t *testing.T) {
+	p := fileutils.GoSourcePath()
+	if !strings.HasSuffix(p, "fileutils/fileutils_test.go") {
+		t.Errorf("GoSourcePath() returned %v", p)
+	}
+}
+
+func TestProjectRoot(t *testing.T) {
+	p := filepath.Join(fileutils.ProjectRoot(), "tint_overrides_with_defaults.gni")
+	if _, err := os.Stat(p); os.IsNotExist(err) {
+		t.Errorf("ProjectRoot() returned %v", p)
+	}
+}