Add --tag-relative flag

This allows you, in combination with the -f flag, to specify whether tag
file names should be relative to the output directory.

README.md

@@ -20,6 +20,7 @@ gotags is a [ctags][]-compatible tag generator for [Go][].
 	-f="": write output to specified file. If file is "-", output is written to standard out.
 	-silent=false: do not produce any output on error.
 	-sort=true: sort tags.
+	-tag-relative=false: file paths should be relative to the directory containing the tag file.
 	-v=false: print version.
 
 ## Vim [Tagbar][] configuration

main.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -27,6 +28,7 @@ var (
 	recurse      bool
 	sortOutput   bool
 	silent       bool
+	relative     bool
 )
 
 // Initialize flags.
@@ -37,6 +39,7 @@ func init() {
 	flag.BoolVar(&recurse, "R", false, "recurse into directories in the file list.")
 	flag.BoolVar(&sortOutput, "sort", true, "sort tags.")
 	flag.BoolVar(&silent, "silent", false, "do not produce any output on error.")
+	flag.BoolVar(&relative, "tag-relative", false, "file paths should be relative to the directory containing the tag file.")
 
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "gotags version %s\n\n", Version)
@@ -145,7 +148,7 @@ func main() {
 
 	tags := []Tag{}
 	for _, file := range files {
-		ts, err := Parse(file)
+		ts, err := Parse(file, relative, path.Dir(outputFile))
 		if err != nil {
 			if !silent {
 				fmt.Fprintf(os.Stderr, "parse error: %s\n\n", err)

parser.go

@@ -5,22 +5,29 @@ import (
 	"go/ast"
 	"go/parser"
 	"go/token"
+	"os"
+	"path/filepath"
 	"strings"
 )
 
 // tagParser contains the data needed while parsing.
 type tagParser struct {
-	fset  *token.FileSet
-	tags  []Tag    // list of created tags
-	types []string // all types we encounter, used to determine the constructors
+	fset     *token.FileSet
+	tags     []Tag    // list of created tags
+	types    []string // all types we encounter, used to determine the constructors
+	relative bool     // should filenames be relative to basepath
+	basepath string   // output file directory
 }
 
-// Parse parses the source in filename and returns a list of tags.
-func Parse(filename string) ([]Tag, error) {
+// Parse parses the source in filename and returns a list of tags. If relative
+// is true, the filenames in the list of tags are relative to basepath.
+func Parse(filename string, relative bool, basepath string) ([]Tag, error) {
 	p := &tagParser{
-		fset:  token.NewFileSet(),
-		tags:  []Tag{},
-		types: make([]string, 0),
+		fset:     token.NewFileSet(),
+		tags:     []Tag{},
+		types:    make([]string, 0),
+		relative: relative,
+		basepath: basepath,
 	}
 
 	f, err := parser.ParseFile(p.fset, filename, nil, 0)
@@ -199,7 +206,16 @@ func (p *tagParser) parseInterfaceMethods(name string, s *ast.InterfaceType) {
 
 // createTag creates a new tag, using pos to find the filename and set the line number.
 func (p *tagParser) createTag(name string, pos token.Pos, tagType TagType) Tag {
-	return NewTag(name, p.fset.File(pos).Name(), p.fset.Position(pos).Line, tagType)
+	f := p.fset.File(pos).Name()
+	if p.relative {
+		if rel, err := filepath.Rel(p.basepath, f); err != nil {
+			// log error, but continue
+			fmt.Fprintf(os.Stderr, "could not determine relative path: %s\n", err)
+		} else {
+			f = rel
+		}
+	}
+	return NewTag(name, f, p.fset.Position(pos).Line, tagType)
 }
 
 // belongsToReceiver checks if a function with these return types belongs to

parser_test.go

@@ -9,6 +9,8 @@ type F map[TagField]string
 
 var testCases = []struct {
 	filename string
+	relative bool
+	basepath string
 	tags     []Tag
 }{
 	{filename: "tests/const.go-src", tags: []Tag{
@@ -82,11 +84,14 @@ var testCases = []struct {
 		tag("C", 8, "v", F{"access": "public"}),
 		tag("D", 9, "v", F{"access": "public"}),
 	}},
+	{filename: "tests/simple.go-src", relative: true, basepath: "dir", tags: []Tag{
+		Tag{Name: "main", File: "../tests/simple.go-src", Address: "1", Type: "p", Fields: F{"line": "1"}},
+	}},
 }
 
 func TestParse(t *testing.T) {
 	for _, testCase := range testCases {
-		tags, err := Parse(testCase.filename)
+		tags, err := Parse(testCase.filename, testCase.relative, testCase.basepath)
 		if err != nil {
 			t.Errorf("[%s] Parse error: %s", testCase.filename, err)
 			continue
@@ -98,7 +103,9 @@ func TestParse(t *testing.T) {
 		}
 
 		for i, tag := range testCase.tags {
-			tag.File = testCase.filename
+			if len(tag.File) == 0 {
+				tag.File = testCase.filename
+			}
 			if tags[i].String() != tag.String() {
 				t.Errorf("[%s] tag(%d)\n  is:%s\nwant:%s", testCase.filename, i, tags[i].String(), tag.String())
 			}

tests/simple.go-src

@@ -0,0 +1 @@
+package main