Add OptSuppressCommon

Add option that supresses common lines.

diff.go

@@ -10,12 +10,29 @@ import (
  "strings"
 )
 
+type config struct {
+ suppressCommon bool
+}
+
+type option func(*config)
+
+// OptSuppressCommon suppresses common lines.
+func OptSuppressCommon() option {
+ return func(c *config) {
+ c.suppressCommon = true
+ }
+}
+
 // Format returns a formatted diff of the two texts,
 // showing the entire text and the minimum line-level
 // additions and removals to turn text1 into text2.
 // (That is, lines only in text1 appear with a leading -,
 // and lines only in text2 appear with a leading +.)
-func Format(text1, text2 string) string {
+func Format(text1, text2 string, options ...option) string {
+ var c config
+ for _, option := range options {
+ option(&c)
+ }
  if text1 != "" && !strings.HasSuffix(text1, "\n") {
  text1 += "(missing final newline)"
  }
@@ -64,14 +81,25 @@ func Format(text1, text2 string) string {
  for i > 0 || j > 0 {
  cost := dist[i][j]
  if i > 0 && j > 0 && cost == dist[i-1][j-1] && lines1[len(lines1)-i] == lines2[len(lines2)-j] {
- fmt.Fprintf(&buf, " %s\n", lines1[len(lines1)-i])
+ if !c.suppressCommon {
+ k := len(lines1) - i
+ fmt.Fprintf(&buf, " %s\n", lines1[k])
+ }
  i--
  j--
  } else if i > 0 && cost == dist[i-1][j]+1 {
- fmt.Fprintf(&buf, "-%s\n", lines1[len(lines1)-i])
+ k := len(lines1) - i
+ if c.suppressCommon {
+ fmt.Fprint(&buf, k+1)
+ }
+ fmt.Fprintf(&buf, "-%s\n", lines1[k])
  i--
  } else {
- fmt.Fprintf(&buf, "+%s\n", lines2[len(lines2)-j])
+ k := len(lines2) - j
+ if c.suppressCommon {
+ fmt.Fprint(&buf, k+1)
+ }
+ fmt.Fprintf(&buf, "+%s\n", lines2[k])
  j--
  }
  }

diff_test.go

@@ -10,16 +10,17 @@ import (
 )
 
 var formatTests = []struct {
- text1 string
- text2 string
- diff string
+ text1 string
+ text2 string
+ diff string
+ suppressCommon string
 }{
- {"a b c", "a b d e f", "a b -c +d +e +f"},
- {"", "a b c", "+a +b +c"},
- {"a b c", "", "-a -b -c"},
- {"a b c", "d e f", "-a -b -c +d +e +f"},
- {"a b c d e f", "a b d e f", "a b -c d e f"},
- {"a b c e f", "a b c d e f", "a b c +d e f"},
+ {"a b c", "a b d e f", "a b -c +d +e +f", "3-c 3+d 4+e 5+f"},
+ {"", "a b c", "+a +b +c", "1+a 2+b 3+c"},
+ {"a b c", "", "-a -b -c", "1-a 2-b 3-c"},
+ {"a b c", "d e f", "-a -b -c +d +e +f", "1-a 2-b 3-c 1+d 2+e 3+f"},
+ {"a b c d e f", "a b d e f", "a b -c d e f", "3-c"},
+ {"a b c e f", "a b c d e f", "a b c +d e f", "4+d"},
 }
 
 func TestFormat(t *testing.T) {
@@ -33,11 +34,25 @@ func TestFormat(t *testing.T) {
  if text2 != "" {
  text2 += "\n"
  }
- out := Format(text1, text2)
- // Cut final \n, cut spaces, turn remaining \n into spaces.
- out = strings.ReplaceAll(strings.ReplaceAll(strings.TrimSuffix(out, "\n"), " ", ""), "\n", " ")
- if out != tt.diff {
- t.Errorf("diff(%q, %q) = %q, want %q", text1, text2, out, tt.diff)
- }
+ compare(t, format, text1, text2, tt.diff)
+ compare(t, suppressCommon, text1, text2, tt.suppressCommon)
+ }
+}
+
+func format(text1, text2 string) string {
+ return Format(text1, text2)
+}
+
+func suppressCommon(text1, text2 string) string {
+ return Format(text1, text2, OptSuppressCommon())
+}
+
+func compare(t *testing.T, testFn func(string, string) string, text1, text2 string, want string) {
+ t.Helper()
+ got := testFn(text1, text2)
+ // Cut final \n, cut spaces, turn remaining \n into spaces.
+ got = strings.ReplaceAll(strings.ReplaceAll(strings.TrimSuffix(got, "\n"), " ", ""), "\n", " ")
+ if got != want {
+ t.Errorf("diff(%q, %q) = %q, want %q", text1, text2, got, want)
  }
 }