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Use custom triple-quote syntax for diffing string literals
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Using strings.Join to denote differences in a multi-line string is
visually noisy due to extensive use of quotes and escape sequences.
Add a custom triple-quote syntax that unambiguously shows line
differences with less visual noise.

If the triple-quote syntax cannot unmabiguously show differences,
then the reporter falls back on using the strings.Join format,
which is never ambiguous.

Fixes #195
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@dsnet
dsnet committed Jun 10, 2020
1 parent a171aa7 commit beb4f6c
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Showing 4 changed files with 366 additions and 8 deletions.
72 changes: 72 additions & 0 deletions cmp/compare_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -902,6 +902,78 @@ func reporterTests() []test {
y: MyComposite{BytesA: []byte(`{"firstName":"John","lastName":"Smith","isAlive":true,"age":27,"address":{"streetAddress":"21 2nd Street","city":"New York","state":"NY","postalCode":"10021-3100"},"phoneNumbers":[{"type":"home","number":"212 555-1234"},{"type":"office","number":"646 555-4567"},{"type":"mobile","number":"123 456-7890"}],"children":[],"spouse":null}`)},
wantEqual: false,
reason: "batched textual diff desired since bytes looks like textual data",
}, {
label: label + "/TripleQuote",
x: MyComposite{StringA: "aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n"},
y: MyComposite{StringA: "aaa\nbbb\nCCC\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nSSS\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n"},
wantEqual: false,
reason: "use triple-quote syntax",
}, {
label: label + "/TripleQuoteSlice",
x: []string{
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
},
y: []string{
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\n",
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
},
wantEqual: false,
reason: "use triple-quote syntax for slices of strings",
}, {
label: label + "/TripleQuoteNamedTypes",
x: MyComposite{
StringB: MyString("aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz"),
BytesC: MyBytes("aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz"),
},
y: MyComposite{
StringB: MyString("aaa\nbbb\nCCC\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nSSS\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz"),
BytesC: MyBytes("aaa\nbbb\nCCC\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nSSS\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz"),
},
wantEqual: false,
reason: "use triple-quote syntax for named types",
}, {
label: label + "/TripleQuoteSliceNamedTypes",
x: []MyString{
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
},
y: []MyString{
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\n",
"aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
},
wantEqual: false,
reason: "use triple-quote syntax for slices of named strings",
}, {
label: label + "/TripleQuoteEndlines",
x: "aaa\nbbb\nccc\nddd\neee\nfff\nggg\r\nhhh\n\riii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n\r",
y: "aaa\nbbb\nCCC\nddd\neee\nfff\nggg\r\nhhh\n\riii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz",
wantEqual: false,
reason: "use triple-quote syntax",
}, {
label: label + "/AvoidTripleQuoteAmbiguousQuotes",
x: "aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
y: "aaa\nbbb\nCCC\nddd\neee\n\"\"\"\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
wantEqual: false,
reason: "avoid triple-quote syntax due to presence of ambiguous triple quotes",
}, {
label: label + "/AvoidTripleQuoteAmbiguousEllipsis",
x: "aaa\nbbb\nccc\n...\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
y: "aaa\nbbb\nCCC\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
wantEqual: false,
reason: "avoid triple-quote syntax due to presence of ambiguous ellipsis",
}, {
label: label + "/AvoidTripleQuoteNonPrintable",
x: "aaa\nbbb\nccc\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
y: "aaa\nbbb\nCCC\nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\no\roo\nppp\nqqq\nrrr\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
wantEqual: false,
reason: "use triple-quote syntax",
}, {
label: label + "/AvoidTripleQuoteIdenticalWhitespace",
x: "aaa\nbbb\nccc\n ddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nRRR\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
y: "aaa\nbbb\nccc \nddd\neee\nfff\nggg\nhhh\niii\njjj\nkkk\nlll\nmmm\nnnn\nooo\nppp\nqqq\nrrr\nsss\nttt\nuuu\nvvv\nwww\nxxx\nyyy\nzzz\n",
wantEqual: false,
reason: "avoid triple-quote syntax due to visual equivalence of differences",
}, {
label: label,
x: MyComposite{
Expand Down
77 changes: 76 additions & 1 deletion cmp/report_slices.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import (
"bytes"
"fmt"
"reflect"
"strconv"
"strings"
"unicode"
"unicode/utf8"
Expand Down Expand Up @@ -96,7 +97,7 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
}
if isText || isBinary {
var numLines, lastLineIdx, maxLineLen int
isBinary = false
isBinary = !utf8.ValidString(sx) || !utf8.ValidString(sy)
for i, r := range sx + sy {
if !(unicode.IsPrint(r) || unicode.IsSpace(r)) || r == utf8.RuneError {
isBinary = true
Expand Down Expand Up @@ -131,6 +132,78 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
},
)
delim = "\n"

// If possible, use a custom triple-quote (""") syntax for printing
// differences in a string literal. This format is more readable,
// but has edge-cases where differences are visually indistinguishable.
// This format is avoided under the following conditions:
// • A line starts with `"""`
// • A line starts with "..."
// • A line contains non-printable characters
// • Adjacent different lines differ only by whitespace
//
// For example:
// """
// ... // 3 identical lines
// foo
// bar
// - baz
// + BAZ
// """
isTripleQuoted := true
prevDiffLines := map[string]bool{}
var list2 textList
list2 = append(list2, textRecord{Value: textLine(`"""`), ElideComma: true})
for _, r := range list {
if !r.Value.Equal(textEllipsis) {
line, _ := strconv.Unquote(string(r.Value.(textLine)))
line = strings.TrimPrefix(strings.TrimSuffix(line, "\r"), "\r") // trim leading/trailing carriage returns for legacy Windows endline support
normLine := strings.Map(func(r rune) rune {
if unicode.IsSpace(r) {
return -1 // drop whitespace to avoid visually indistinguishable output
}
return r
}, line)
isPrintable := func(r rune) bool {
return unicode.IsPrint(r) || r == '\t' // specially treat tab as printable
}
isTripleQuoted = isTripleQuoted &&
!strings.HasPrefix(line, `"""`) &&
!strings.HasPrefix(line, "...") &&
strings.TrimFunc(line, isPrintable) == "" &&
(r.Diff == 0 || !prevDiffLines[normLine])
if !isTripleQuoted {
break
}
r.Value = textLine(line)
r.ElideComma = true
prevDiffLines[normLine] = true
}
if r.Diff == 0 {
prevDiffLines = map[string]bool{} // start a new non-adjacent difference group
}
list2 = append(list2, r)
}
if r := list2[len(list2)-1]; r.Diff == diffIdentical && len(r.Value.(textLine)) == 0 {
list2 = list2[:len(list2)-1] // elide single empty line at the end
}
list2 = append(list2, textRecord{Value: textLine(`"""`), ElideComma: true})
if isTripleQuoted {
var out textNode = textWrap{"(", list2, ")"}
switch t.Kind() {
case reflect.String:
if t != reflect.TypeOf(string("")) {
out = opts.FormatType(t, out)
}
case reflect.Slice:
// Always emit type for slices since the triple-quote syntax
// looks like a string (not a slice).
opts = opts.WithTypeMode(emitType)
out = opts.FormatType(t, out)
}
return out
}

// If the text appears to be single-lined text,
// then perform differencing in approximately fixed-sized chunks.
// The output is printed as quoted strings.
Expand All @@ -143,6 +216,7 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
},
)
delim = ""

// If the text appears to be binary data,
// then perform differencing in approximately fixed-sized chunks.
// The output is inspired by hexdump.
Expand All @@ -159,6 +233,7 @@ func (opts formatOptions) FormatDiffSlice(v *valueNode) textNode {
return textRecord{Diff: d, Value: textLine(s), Comment: comment}
},
)

// For all other slices of primitive types,
// then perform differencing in approximately fixed-sized chunks.
// The size of each chunk depends on the width of the element kind.
Expand Down
15 changes: 8 additions & 7 deletions cmp/report_text.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -138,10 +138,11 @@ func (s textWrap) formatExpandedTo(b []byte, d diffMode, n indentMode) []byte {
// of the textList.formatCompactTo method.
type textList []textRecord
type textRecord struct {
Diff diffMode // e.g., 0 or '-' or '+'
Key string // e.g., "MyField"
Value textNode // textWrap | textLine
Comment fmt.Stringer // e.g., "6 identical fields"
Diff diffMode // e.g., 0 or '-' or '+'
Key string // e.g., "MyField"
Value textNode // textWrap | textLine
ElideComma bool // avoid trailing comma
Comment fmt.Stringer // e.g., "6 identical fields"
}

// AppendEllipsis appends a new ellipsis node to the list if none already
Expand All @@ -151,9 +152,9 @@ func (s *textList) AppendEllipsis(ds diffStats) {
hasStats := ds != diffStats{}
if len(*s) == 0 || !(*s)[len(*s)-1].Value.Equal(textEllipsis) {
if hasStats {
*s = append(*s, textRecord{Value: textEllipsis, Comment: ds})
*s = append(*s, textRecord{Value: textEllipsis, ElideComma: true, Comment: ds})
} else {
*s = append(*s, textRecord{Value: textEllipsis})
*s = append(*s, textRecord{Value: textEllipsis, ElideComma: true})
}
return
}
Expand Down Expand Up @@ -292,7 +293,7 @@ func (s textList) formatExpandedTo(b []byte, d diffMode, n indentMode) []byte {
b = alignKeyLens[i].appendChar(b, ' ')

b = r.Value.formatExpandedTo(b, d|r.Diff, n)
if !r.Value.Equal(textEllipsis) {
if !r.ElideComma {
b = append(b, ',')
}
b = alignValueLens[i].appendChar(b, ' ')
Expand Down
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