Implement -format=json (for vim-go)

related to #1

expanderr.go

@@ -8,6 +8,7 @@ package main
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -561,6 +562,7 @@ func logic(w io.Writer, buildctx *build.Context, posn string) error {
 	if _, err := src.Write(b[:subject.Pos()-1]); err != nil {
 		return err
 	}
+	var newEnd int
 	// Print the replacement
 	for _, node := range repl {
 		// Hack: inline comments (e.g. os.Remove("/foo" /* path */)) get lost
@@ -574,6 +576,8 @@ func logic(w io.Writer, buildctx *build.Context, posn string) error {
 			return fmt.Errorf("formatting replacement: %v", err)
 		}
 
+		newEnd += len(strings.Split(stmtFmt.String(), "\n"))
+
 		ceOrig := string(b[e.ce.Pos()-1 : e.ce.End()-1])
 		if _, err := src.Write([]byte(strings.Replace(stmtFmt.String(), ceFmt.String(), ceOrig, 1))); err != nil {
 			return err
@@ -595,14 +599,39 @@ func logic(w io.Writer, buildctx *build.Context, posn string) error {
 		return fmt.Errorf("formatting source: %v.\nsource:\n%s", err, src.String())
 	}
 
-	if _, err := w.Write(formatted); err != nil {
-		return err
+	if *formatFlag == "json" {
+		start := e.fset.Position(subject.Pos()).Line
+		end := e.fset.Position(subject.End()).Line
+		var lines []string
+		for idx, line := range strings.Split(string(formatted), "\n") {
+			if idx >= start-1 && idx < start-1+newEnd {
+				lines = append(lines, line)
+			}
+		}
+		if err := json.NewEncoder(w).Encode(struct {
+			Start int      `json:"start"`
+			End   int      `json:"end"`
+			Lines []string `json:"lines"`
+		}{
+			Start: start,
+			End:   end,
+			Lines: lines,
+		}); err != nil {
+			return err
+		}
+	} else {
+		if _, err := w.Write(formatted); err != nil {
+			return err
+		}
 	}
 
 	return nil
 }
 
-var wFlag = flag.String("w", "", "write")
+var (
+	wFlag      = flag.String("w", "", "write")
+	formatFlag = flag.String("format", "", "output format (source, json). defaults to 'source'")
+)
 
 var cpuprofile = flag.String("cpuprofile", "", "write cpu profile `file`")
 

expanderr_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"bytes"
+	"encoding/json"
+	"flag"
 	"go/build"
 	"io/ioutil"
 	"path/filepath"
@@ -42,6 +44,8 @@ func TestExpand(t *testing.T) {
 			// Cannot be safely run in parallel as long as build.Default is overridden
 			// t.Parallel()
 
+			flag.Set("format", "source")
+
 			wantContents, err := ioutil.ReadFile(strings.Replace(entry.fn, ".got", ".want", 1))
 			if err != nil {
 				t.Fatal(err)
@@ -67,6 +71,40 @@ func TestExpand(t *testing.T) {
 			if got, want := buf.String(), string(wantContents); got != want {
 				t.Fatalf("unexpected result: have:\n%s\nwant:\n%s", got, want)
 			}
+
+			// Test the JSON output format as well.
+
+			buf.Reset()
+			flag.Set("format", "json")
+
+			gotContents, err := ioutil.ReadFile(entry.fn)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if err := logic(&buf, &buildctx, entry.fn+entry.posn); err != nil {
+				t.Fatal(err)
+			}
+
+			var change struct {
+				Start int      `json:"start"`
+				End   int      `json:"end"`
+				Lines []string `json:"lines"`
+			}
+			if err := json.Unmarshal(buf.Bytes(), &change); err != nil {
+				t.Fatal(err)
+			}
+
+			lines := strings.Split(string(gotContents), "\n")
+
+			replaced := make([]string, len(lines[:change.Start-1]))
+			copy(replaced, lines)
+			replaced = append(replaced, change.Lines...)
+			replaced = append(replaced, lines[change.End:]...)
+
+			if got, want := strings.Join(replaced, "\n"), string(wantContents); got != want {
+				t.Fatalf("unexpected result: have:\n%s\nwant:\n%s", got, want)
+			}
 		})
 	}
 }