Don't depend on working directory in folders.FindDirWithLeaf (#54)

This is plumbing for allowing a configurable root that doesn't depend on
the working directory.

folders/folders.go

@@ -2,30 +2,33 @@ package folders
 
 import (
 	"errors"
-	"fmt"
 	"os"
-	"path"
+	"path/filepath"
 )
 
-func FindDirWithLeaf(leaf string) (string, error) {
-	dir, err := os.Getwd()
-	if err != nil {
-		return "", fmt.Errorf("cannot find $PWD: %s", err)
-	}
+// FindDirWithLeaf returns the first directory that holds `leaf`,
+// traversing up to the root of the filesystem, starting at `dir`.
+func FindDirWithLeaf(dir string, leaf string) (string, error) {
 	for {
-		_, err = os.Stat(fmt.Sprintf("%s/%s", dir, leaf))
+		_, err := os.Stat(filepath.Join(dir, leaf))
+
+		// No error means we found the leaf in dir.
+		if err == nil {
+			return dir, nil
+		}
+
+		// ErrNotExist means we continue traversal up the tree.
 		if errors.Is(err, os.ErrNotExist) {
-			// TODO: test on windows
-			next := path.Dir(dir)
-			if dir == next { // or stop at $HOME?..
-				return "", fmt.Errorf("cannot find %s anywhere", leaf)
+			next := filepath.Dir(dir)
+			if dir == next {
+				// Return if we cannot continue traversal.
+				return "", err
 			}
+
 			dir = next
 			continue
 		}
-		if err != nil {
-			return "", err
-		}
-		return dir, nil
+
+		return "", err
 	}
 }

folders/folders_test.go

@@ -0,0 +1,38 @@
+package folders
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFindDirWithLeaf(t *testing.T) {
+	wd, err := os.Getwd()
+	require.NoError(t, err)
+
+	root := filepath.Join(wd, "..")
+
+	// Find from working directory should work.
+	{
+		out, err := FindDirWithLeaf(wd, ".git")
+		assert.NoError(t, err)
+		assert.Equal(t, out, root)
+	}
+
+	// Find from project root itself should work.
+	{
+		out, err := FindDirWithLeaf(root, ".git")
+		assert.NoError(t, err)
+		assert.Equal(t, out, root)
+	}
+
+	// Find for something that doesn't exist should work.
+	{
+		out, err := FindDirWithLeaf(root, "this-leaf-doesnt-exist-anywhere")
+		assert.ErrorIs(t, err, os.ErrNotExist)
+		assert.Equal(t, out, "")
+	}
+}

git/git.go

@@ -3,6 +3,7 @@ package git
 import (
 	"fmt"
 	"net/url"
+	"os"
 	"path"
 	"strings"
 
@@ -12,7 +13,11 @@ import (
 )
 
 func Root() (string, error) {
-	return folders.FindDirWithLeaf(".git")
+	wd, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	return folders.FindDirWithLeaf(wd, ".git")
 }
 
 // Origin finds the git repository the project is cloned from, so that

project/config.go

@@ -1,6 +1,7 @@
 package project
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -104,5 +105,15 @@ func validateAndApplyProjectDefaults(prj Project) (Project, error) {
 }
 
 func findProjectRoot() (string, error) {
-	return folders.FindDirWithLeaf(ConfigFile)
+	wd, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	dir, err := folders.FindDirWithLeaf(wd, ConfigFile)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return "", fmt.Errorf("cannot find %s anywhere", ConfigFile)
+		}
+	}
+	return dir, nil
 }