[pkg] Fine-tune error messages

pkg/README.md

@@ -22,14 +22,19 @@ This section is empty.
 
 ## Variables
 
+<pre>
+var ErrModuleNameMissing = errors.New("failed to find module name")
+var ErrGoModMissing = errors.New("unable to find go.mod")
+</pre>
 <pre>
 var Markdown string // value from template.md file
+var ErrManyPackagesInDir = errors.New("can only handle one package per directory")
 var ErrNoPackageFound = errors.New("couldn't find package from ")
 </pre>
 
 ## Functions
 
-### func [RunDirTree](./run.go#L132)
+### func [RunDirTree](./run.go#L131)
 
 <pre>
 func RunDirTree(out <a href="#type-outputsettings">OutputSettings</a>, version string, includeMain bool) error
@@ -38,7 +43,7 @@ RunDirTree checks given directory and its subdirectories with RunDirectory().
 Ignores all ErrNoPackageFound errors from RunDirectory.
 
 
-### func [RunDirectory](./run.go#L122)
+### func [RunDirectory](./run.go#L121)
 
 <pre>
 func RunDirectory(out <a href="#type-outputsettings">OutputSettings</a>, version string, includeMain bool) error
@@ -57,7 +62,7 @@ type OutputSettings struct {
     Filename string
 }
 </pre>
-### func (output *OutputSettings) [Writer](./run.go#L108)
+### func (output *OutputSettings) [Writer](./run.go#L107)
 <pre>
 func (output *OutputSettings) Writer() (<a href="https://pkg.go.dev/io#WriteCloser">io.WriteCloser</a>, error)
 </pre>

pkg/mod.go

@@ -3,13 +3,19 @@ package pkg
 import (
 	"bufio"
 	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
 
 	log "github.com/sirupsen/logrus"
 )
 
+var (
+	ErrModuleNameMissing = errors.New("failed to find module name")
+	ErrGoModMissing      = errors.New("unable to find go.mod")
+)
+
 func hasGoMod(dir string) bool {
 	// log.Info("Checking " + dir)
 	_, err := os.Stat(dir + "/go.mod")
@@ -19,8 +25,9 @@ func hasGoMod(dir string) bool {
 func moduleName(dir string) (string, error) {
 	f, err := os.Open(dir + "/go.mod")
 	if err != nil {
-		log.WithFields(log.Fields{"dir": dir, "err": err}).Error("Failed to open go.mod")
-		return "", errors.New("failed to open go.mod")
+		err = fmt.Errorf("moduleName failed: %w", err)
+		log.WithFields(log.Fields{"dir": dir}).Error(err)
+		return "", err
 	}
 	defer f.Close()
 	scan := bufio.NewScanner(f)
@@ -35,28 +42,29 @@ func moduleName(dir string) (string, error) {
 			log.WithFields(log.Fields{"line": line}).Error("module name missing from line")
 		}
 	}
-	return "", errors.New("failed to find module name from go.mod")
+	return "", fmt.Errorf("%w from %s/go.mod", ErrModuleNameMissing, dir)
 }
 
 // getPackageName assumes that each directory has one package name in golang namespace.
 func getPackageName(dir string) (string, error) {
 	cwd, err := filepath.Abs(dir)
 	if err != nil {
-		return "", errors.New("unable to determine absolute path")
+		return "", fmt.Errorf("getPackageName failed: %w", err)
 	}
 	dirs := strings.Split(cwd, "/")
-	for join := len(dirs); join > 0; join-- {
-		current := strings.Join(dirs[0:join], "/")
-		if hasGoMod(current) {
-			mod, err := moduleName(current)
-			if err != nil {
-				return "", err
-			}
-			parts := append([]string{mod}, dirs[join:]...)
-			return strings.Join(parts, "/"), nil
+	for idx := len(dirs); idx > 0; idx-- {
+		root := strings.Join(dirs[0:idx], "/")
+		if !hasGoMod(root) {
+			continue
+		}
+		modName, err := moduleName(root)
+		if err != nil {
+			return "", err
 		}
+		parts := append([]string{modName}, dirs[idx:]...)
+		return strings.Join(parts, "/"), nil
 	}
-	return "", errors.New("unable to find go.mod with module name")
+	return "", fmt.Errorf("%w from %s or its parent dirs", ErrGoModMissing, cwd)
 }
 
 func fileExists(fname string) bool {

pkg/run.go

@@ -40,8 +40,9 @@ var (
 	// Markdown is golang template for go2md output
 	//
 	//go:embed template.md
-	Markdown          string // value from template.md file
-	ErrNoPackageFound = errors.New("couldn't find package from ")
+	Markdown             string // value from template.md file
+	ErrManyPackagesInDir = errors.New("can only handle one package per directory")
+	ErrNoPackageFound    = errors.New("couldn't find package from ")
 )
 
 // isProductionGo ignores all code that is only used for `go test`
@@ -57,11 +58,11 @@ func getImportsFromFile(specs []*ast.ImportSpec) map[string]string {
 	for _, spec := range specs {
 		path := strings.Trim(spec.Path.Value, ("\""))
 		switch {
-		case spec.Name == nil:
+		case spec.Name == nil: // import "github.com/..."
 			fields := strings.Split(path, "/")
 			imported[fields[len(fields)-1]] = path
-		case spec.Name.Name == "_": // ignore
-		default:
+		case spec.Name.Name == "_": // ignore import _ "github.com/..."
+		default: // import alias "github.com/..."
 			imported[spec.Name.Name] = path
 		}
 	}
@@ -120,7 +121,7 @@ func (output *OutputSettings) Writer() (io.WriteCloser, error) {
 func RunDirectory(out OutputSettings, version string, includeMain bool) error {
 	pkgName, err := getPackageName(out.Directory)
 	if err != nil {
-		return fmt.Errorf("failed determine module name: %w", err)
+		return err
 	}
 	return run(out, pkgName, version, includeMain)
 }
@@ -245,7 +246,7 @@ func getPackage(directory, modName string, includeMain bool) (*packageInfo, erro
 	for _, pkg := range pkgs {
 		names = append(names, pkg.Name)
 	}
-	return nil, fmt.Errorf("can only handle one package per directory (found: %s)", strings.Join(names, ", "))
+	return nil, fmt.Errorf("%w (found: %s)", ErrManyPackagesInDir, strings.Join(names, ", "))
 }
 
 // Run reads all "*.go" files (excluding "*_test.go") and writes markdown document out of it.