Add goimports flag.

README.md

@@ -25,15 +25,16 @@ Depending on how you prefer to structure your code, you can either
 
 The following flags are defined by the binary.
 
-| Name               | Short Flag | Description                                                                                                                |
-| ------------------ | ---------- | -------------------------------------------------------------------------------------------------------------------------- |
-| package            | p          | The name of the generated package. Is the name of target directory if dirname or filename is supplied by default.          |
-| prefix             |            | A prefix used in the name of each mock struct. Should be TitleCase by convention.                                          |
-| interfaces         | i          | A whitelist of interfaces to generate given the import paths.                                                              |
-| filename           | o          | The target output file. All mocks are written to this file.                                                                |
-| dirname            | d          | The target output directory. Each mock will be written to a unique file.                                                   |
-| force              | f          | Do not abort if a write to disk would overwrite an existing file.                                                          |
-| disable-formatting |            | Do not run goimports over the rendered files. Formatting is enabled by default and requires `goimports` to be on the PATH. |
+| Name               | Short Flag | Description                                                                                                       |
+| ------------------ | ---------- | ----------------------------------------------------------------------------------------------------------------- |
+| package            | p          | The name of the generated package. Is the name of target directory if dirname or filename is supplied by default. |
+| prefix             |            | A prefix used in the name of each mock struct. Should be TitleCase by convention.                                 |
+| interfaces         | i          | A whitelist of interfaces to generate given the import paths.                                                     |
+| filename           | o          | The target output file. All mocks are written to this file.                                                       |
+| dirname            | d          | The target output directory. Each mock will be written to a unique file.                                          |
+| force              | f          | Do not abort if a write to disk would overwrite an existing file.                                                 |
+| disable-formatting |            | Do not run goimports over the rendered files (enabled by default).                                                |
+| goimports          |            | Path to the goimports binary (uses goimports on your PATH by default).                                            |
 
 If neither dirname nor filename are supplied, then the generated code is written to a unique file in the current directory.
 

cmd/go-mockgen/args.go

@@ -30,6 +30,7 @@ func parseArgs() (*generation.Options, error) {
 	app.Flag("prefix", "A prefix used in the name of each mock struct. Should be TitleCase by convention.").StringVar(&opts.Prefix)
 	app.Flag("force", "Do not abort if a write to disk would overwrite an existing file.").Short('f').BoolVar(&opts.Force)
 	app.Flag("disable-formatting", "Do not run goimports over the rendered files.").BoolVar(&opts.DisableFormatting)
+	app.Flag("goimports", "Path to the goimports binary.").Default("goimports").StringVar(&opts.GoImportsBinary)
 
 	if _, err := app.Parse(os.Args[1:]); err != nil {
 		return nil, err

cmd/go-mockgen/main.go

@@ -16,10 +16,26 @@ func init() {
 
 func main() {
 	if err := mainErr(); err != nil {
-		log.Fatalf("error: %s\n", err.Error())
+		message := fmt.Sprintf("error: %s\n", err.Error())
+
+		if solvableError, ok := err.(solvableError); ok {
+			message += "\nPossible solutions:\n"
+
+			for _, hint := range solvableError.Solutions() {
+				message += fmt.Sprintf("  - %s\n", hint)
+			}
+
+			message += "\n"
+		}
+
+		log.Fatalf(message)
 	}
 }
 
+type solvableError interface {
+	Solutions() []string
+}
+
 func mainErr() error {
 	opts, err := parseArgs()
 	if err != nil {

internal/mockgen/generation/generate.go

@@ -85,8 +85,15 @@ func generateAndRender(ifaces []*types.Interface, filename string, opts *Options
 	}
 
 	if !opts.DisableFormatting {
-		if err := exec.Command("goimports", "-w", filename).Run(); err != nil {
-			return fmt.Errorf("failed format file (install goimports on your PATH or run go-mockgen with --disable-formatting): %s", err)
+		if err := exec.Command(opts.GoImportsBinary, "-w", filename).Run(); err != nil {
+			return errorWithSolutions{
+				err: fmt.Errorf("failed to format file: %s", err),
+				solutions: []string{
+					"install goimports on your PATH",
+					"specify a non-standard path to a goimports binary via --goimports",
+					"disable post-render formatting via --disable-formatting",
+				},
+			}
 		}
 	}
 
@@ -109,3 +116,11 @@ func generateContent(ifaces []*types.Interface, pkgName, prefix, outputImportPat
 
 	return buffer.String(), nil
 }
+
+type errorWithSolutions struct {
+	err       error
+	solutions []string
+}
+
+func (e errorWithSolutions) Error() string       { return e.err.Error() }
+func (e errorWithSolutions) Solutions() []string { return e.solutions }

internal/mockgen/generation/options.go

@@ -10,4 +10,5 @@ type Options struct {
 	Prefix            string
 	Force             bool
 	DisableFormatting bool
+	GoImportsBinary   string
 }