Add positive tests for TextFragment#ApplyStrict

These cover all of the cases (I think) where application should succeed.

gitdiff/apply.go

@@ -122,19 +122,22 @@ func (f *TextFragment) ApplyStrict(dst io.Writer, src LineReader) error {
 		return applyError(err, lineNum(n))
 	}
 
+	used := int64(0)
 	for i, line := range f.Lines {
-		fromSrc, err := applyTextLine(dst, nextLine, line)
-		if err != nil {
+		if err := applyTextLine(dst, nextLine, line); err != nil {
 			return applyError(err, lineNum(n), fragLineNum(i))
 		}
-
-		if fromSrc && i < len(f.Lines)-1 {
+		if fromSrc(line) {
+			used++
+		}
+		// advance reader if the next fragment line appears in src and we're behind
+		if i < len(f.Lines)-1 && fromSrc(f.Lines[i+1]) && int64(n)-limit < used {
 			nextLine, n, err = src.ReadLine()
 			if err != nil {
 				if err == io.EOF {
 					err = io.ErrUnexpectedEOF
 				}
-				return applyError(err, lineNum(n), fragLineNum(i+1))
+				return applyError(err, lineNum(n), fragLineNum(i+1)) // report for _next_ line in fragment
 			}
 		}
 	}
@@ -142,12 +145,11 @@ func (f *TextFragment) ApplyStrict(dst io.Writer, src LineReader) error {
 	return nil
 }
 
-func applyTextLine(dst io.Writer, src string, line Line) (fromSrc bool, err error) {
+func applyTextLine(dst io.Writer, src string, line Line) (err error) {
 	switch line.Op {
 	case OpContext, OpDelete:
-		fromSrc = true
 		if src != line.Line {
-			return fromSrc, conflictError("fragment line does not match src line")
+			return conflictError("fragment line does not match src line")
 		}
 	}
 	switch line.Op {
@@ -157,6 +159,10 @@ func applyTextLine(dst io.Writer, src string, line Line) (fromSrc bool, err erro
 	return
 }
 
+func fromSrc(line Line) bool {
+	return line.Op != OpAdd
+}
+
 // copyLines copies from src to dst until the line at limit, exclusive. Returns
 // the line at limit and the line number. The line number may not equal the
 // limit if and only if a non-EOF error occurs. A negative limit means the

gitdiff/apply_test.go

@@ -0,0 +1,66 @@
+package gitdiff
+
+import (
+	"bytes"
+	"io/ioutil"
+	"path/filepath"
+	"testing"
+)
+
+func TestTextFragmentApplyStrict(t *testing.T) {
+	tests := map[string]struct {
+		File string
+		Err  bool
+	}{
+		"createFile":   {File: "new"},
+		"deleteFile":   {File: "delete_all"},
+		"addStart":     {File: "add_start"},
+		"addMiddle":    {File: "add_middle"},
+		"addEnd":       {File: "add_end"},
+		"changeStart":  {File: "change_start"},
+		"changeMiddle": {File: "change_middle"},
+		"changeEnd":    {File: "change_end"},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			base := filepath.Join("testdata", "apply", "text_fragment_"+test.File)
+
+			src, err := ioutil.ReadFile(base + ".src")
+			if err != nil {
+				t.Fatalf("failed to read source file: %v", err)
+			}
+			patch, err := ioutil.ReadFile(base + ".patch")
+			if err != nil {
+				t.Fatalf("failed to read patch file: %v", err)
+			}
+			result, err := ioutil.ReadFile(base + ".dst")
+			if err != nil {
+				t.Fatalf("failed to read result file: %v", err)
+			}
+
+			files, _, err := Parse(bytes.NewReader(patch))
+			if err != nil {
+				t.Fatalf("failed to parse patch file: %v", err)
+			}
+
+			frag := files[0].TextFragments[0]
+
+			var dst bytes.Buffer
+			err = frag.ApplyStrict(&dst, NewLineReader(bytes.NewReader(src), 0))
+			if test.Err {
+				if err == nil {
+					t.Fatalf("expected error applying fragment, but got nil")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error applying fragment: %v", err)
+			}
+
+			if !bytes.Equal(result, dst.Bytes()) {
+				t.Errorf("incorrect result after apply\nexpected:\n%s\nactual:\n%s", result, dst.Bytes())
+			}
+		})
+	}
+}

gitdiff/testdata/apply/text_fragment_add_end.dst

@@ -0,0 +1,5 @@
+line 1
+line 2
+line 3
+new line a
+new line b

gitdiff/testdata/apply/text_fragment_add_end.patch

@@ -0,0 +1,9 @@
+diff --git a/gitdiff/testdata/apply/fragment_add_end.src b/gitdiff/testdata/apply/fragment_add_end.src
+--- a/gitdiff/testdata/apply/fragment_add_end.src
++++ b/gitdiff/testdata/apply/fragment_add_end.src
+@@ -1,3 +1,5 @@
+ line 1
+ line 2
+ line 3
++new line a
++new line b

gitdiff/testdata/apply/text_fragment_add_end.src

@@ -0,0 +1,3 @@
+line 1
+line 2
+line 3

gitdiff/testdata/apply/text_fragment_add_middle.dst

@@ -0,0 +1,5 @@
+line 1
+line 2
+new line a
+new line b
+line 3

gitdiff/testdata/apply/text_fragment_add_middle.patch

@@ -0,0 +1,9 @@
+diff --git a/gitdiff/testdata/apply/fragment_add_middle.src b/gitdiff/testdata/apply/fragment_add_middle.src
+--- a/gitdiff/testdata/apply/fragment_add_middle.src
++++ b/gitdiff/testdata/apply/fragment_add_middle.src
+@@ -1,3 +1,5 @@
+ line 1
+ line 2
++new line a
++new line b
+ line 3

gitdiff/testdata/apply/text_fragment_add_middle.src

@@ -0,0 +1,3 @@
+line 1
+line 2
+line 3

gitdiff/testdata/apply/text_fragment_add_start.dst

@@ -0,0 +1,4 @@
+new line a
+line 1
+line 2
+line 3

gitdiff/testdata/apply/text_fragment_add_start.patch

@@ -0,0 +1,8 @@
+diff --git a/gitdiff/testdata/apply/fragment_add_start.src b/gitdiff/testdata/apply/fragment_add_start.src
+--- a/gitdiff/testdata/apply/fragment_add_start.src
++++ b/gitdiff/testdata/apply/fragment_add_start.src
+@@ -1,3 +1,4 @@
++new line a
+ line 1
+ line 2
+ line 3

gitdiff/testdata/apply/text_fragment_add_start.src

@@ -0,0 +1,3 @@
+line 1
+line 2
+line 3

gitdiff/testdata/apply/text_fragment_change_end.dst

@@ -0,0 +1,10 @@
+line 1
+line 2
+line 3
+line 4
+line 5
+line 6
+line 7
+line 8
+line 9
+new line a

gitdiff/testdata/apply/text_fragment_change_end.patch

@@ -0,0 +1,9 @@
+diff --git a/gitdiff/testdata/apply/text_fragment_change_end.src b/gitdiff/testdata/apply/text_fragment_change_end.src
+--- a/gitdiff/testdata/apply/text_fragment_change_end.src
++++ b/gitdiff/testdata/apply/text_fragment_change_end.src
+@@ -7,4 +7,4 @@ line 6
+ line 7
+ line 8
+ line 9
+-line 10
++new line a

gitdiff/testdata/apply/text_fragment_change_end.src

@@ -0,0 +1,10 @@
+line 1
+line 2
+line 3
+line 4
+line 5
+line 6
+line 7
+line 8
+line 9
+line 10

gitdiff/testdata/apply/text_fragment_change_middle.dst

@@ -0,0 +1,9 @@
+line 1
+line 2
+line 3
+line 4
+line 5
+new line a
+line 7
+line 8
+line 9

gitdiff/testdata/apply/text_fragment_change_middle.patch

@@ -0,0 +1,12 @@
+diff --git a/gitdiff/testdata/apply/text_fragment_change_middle.src b/gitdiff/testdata/apply/text_fragment_change_middle.src
+--- a/gitdiff/testdata/apply/text_fragment_change_middle.src
++++ b/gitdiff/testdata/apply/text_fragment_change_middle.src
+@@ -3,7 +3,7 @@ line 2
+ line 3
+ line 4
+ line 5
+-line 6
++new line a
+ line 7
+ line 8
+ line 9

gitdiff/testdata/apply/text_fragment_change_middle.src

@@ -0,0 +1,10 @@
+line 1
+line 2
+line 3
+line 4
+line 5
+line 6
+line 7
+line 8
+line 9
+line 10

gitdiff/testdata/apply/text_fragment_change_start.dst

@@ -0,0 +1,4 @@
+new line a
+line 2
+line 3
+line 4

gitdiff/testdata/apply/text_fragment_change_start.patch

@@ -0,0 +1,9 @@
+diff --git a/gitdiff/testdata/apply/text_fragment_change_start.src b/gitdiff/testdata/apply/text_fragment_change_start.src
+--- a/gitdiff/testdata/apply/text_fragment_change_start.src
++++ b/gitdiff/testdata/apply/text_fragment_change_start.src
+@@ -1,4 +1,4 @@
+-line 1
++new line a
+ line 2
+ line 3
+ line 4

gitdiff/testdata/apply/text_fragment_change_start.src

@@ -0,0 +1,10 @@
+line 1
+line 2
+line 3
+line 4
+line 5
+line 6
+line 7
+line 8
+line 9
+line 10

gitdiff/testdata/apply/text_fragment_delete_all.patch

@@ -0,0 +1,8 @@
+diff --git a/gitdiff/testdata/apply/fragment_delete_all.src b/gitdiff/testdata/apply/fragment_delete_all.src
+--- a/gitdiff/testdata/apply/fragment_delete_all.src
++++ b/gitdiff/testdata/apply/fragment_delete_all.src
+@@ -1,4 +0,0 @@
+-line a
+-line b
+-line c
+-line d

gitdiff/testdata/apply/text_fragment_delete_all.src

@@ -0,0 +1,4 @@
+line a
+line b
+line c
+line d

gitdiff/testdata/apply/text_fragment_new.dst

@@ -0,0 +1,3 @@
+line 1
+line 2
+line 3

gitdiff/testdata/apply/text_fragment_new.patch

@@ -0,0 +1,7 @@
+diff --git a/gitdiff/testdata/apply/fragment_new.src b/gitdiff/testdata/apply/fragment_new.src
+--- a/gitdiff/testdata/apply/fragment_new.src
++++ b/gitdiff/testdata/apply/fragment_new.src
+@@ -0,0 +1,3 @@
++line 1
++line 2
++line 3