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Migrate error comparisons to errors.Is/errors.As #84

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Migrate error comparisons to errors.Is/errors.As #84

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24 changes: 15 additions & 9 deletions diff/parse.go
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Original file line number Diff line number Diff line change
Expand Up @@ -74,9 +74,11 @@ func (r *MultiFileDiffReader) ReadFileWithTrailingContent() (*FileDiff, string,

fd, err := fr.ReadAllHeaders()
if err != nil {
switch e := err.(type) {
case *ParseError:
if e.Err == ErrNoFileHeader || e.Err == ErrExtendedHeadersEOF {
var pe *ParseError
var oe OverflowError
switch {
case errors.As(err, &pe):
if errors.Is(pe.Err, ErrNoFileHeader) || errors.Is(pe.Err, ErrExtendedHeadersEOF) {
// Any non-diff content preceding a valid diff is included in the
// extended headers of the following diff. In this way, mixed diff /
// non-diff content can be parsed. Trailing non-diff content is
Expand All @@ -91,8 +93,8 @@ func (r *MultiFileDiffReader) ReadFileWithTrailingContent() (*FileDiff, string,
}
return nil, "", err

case OverflowError:
r.nextFileFirstLine = []byte(e)
case errors.As(err, &oe):
r.nextFileFirstLine = []byte(oe)
return fd, "", nil

default:
Expand Down Expand Up @@ -124,8 +126,10 @@ func (r *MultiFileDiffReader) ReadFileWithTrailingContent() (*FileDiff, string,
r.line = fr.line
r.offset = fr.offset
if err != nil {
if e0, ok := err.(*ParseError); ok {
if e, ok := e0.Err.(*ErrBadHunkLine); ok {
var e0 *ParseError
if errors.As(err, &e0) {
var e *ErrBadHunkLine
if errors.As(e0.Err, &e) {

@keegancsmith keegancsmith Jun 17, 2026

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We should add the Unwrap method to ParseError in this PR then we can simplify this and other places so we don't first have to check for ParseError

// This just means we finished reading the hunks for the
// current file. See the ErrBadHunkLine doc for more info.
r.nextFileFirstLine = e.Line
Expand Down Expand Up @@ -224,13 +228,15 @@ func (r *FileDiffReader) ReadAllHeaders() (*FileDiff, error) {
fd := &FileDiff{}

fd.Extended, err = r.ReadExtendedHeaders()
if pe, ok := err.(*ParseError); ok && pe.Err == ErrExtendedHeadersEOF {
var pe *ParseError
var oe OverflowError
if errors.As(err, &pe) && errors.Is(pe.Err, ErrExtendedHeadersEOF) {

@keegancsmith keegancsmith Jun 17, 2026

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code like this make me nervous in general, but I believe its correct. IE we are relying on the first condition to mutate pe so that the second condition doesn't nil panic on pe.Err

wasEmpty := handleEmpty(fd)
if wasEmpty {
return fd, nil
}
return fd, err
} else if _, ok := err.(OverflowError); ok {
} else if errors.As(err, &oe) {
handleEmpty(fd)
return fd, err
} else if err != nil {
Expand Down
2 changes: 1 addition & 1 deletion diff/reader_util.go
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ func (l *lineReader) nextNextLineStartsWith(prefix string) (bool, error) {
// false and ignore the error when readErr is io.EOF.
func (l *lineReader) lineHasPrefix(line []byte, prefix string, readErr error) (bool, error) {
if readErr != nil {
if readErr == io.EOF || readErr == bufio.ErrBufferFull {
if readErr == io.EOF || errors.Is(readErr, bufio.ErrBufferFull) {
return false, nil
}
return false, readErr
Expand Down
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