MM-29981 - optimize markdown.Inspect (#16188)

* MM-29981 - optimize markdown.Inspect

- Cache regexp.MustCompile
- Reuse slice in MergeInlineText
- Remove pointer to slice in closeBlocks
- Pre-allocate slice in ParseLines
- Some more small cleanups

```
name       old time/op    new time/op    delta
Inspect-8    10.5µs ± 3%     6.6µs ± 1%  -37.59%  (p=0.000 n=10+7)

name       old alloc/op   new alloc/op   delta
Inspect-8    6.66kB ± 0%    3.22kB ± 0%  -51.62%  (p=0.000 n=10+9)

name       old allocs/op  new allocs/op  delta
Inspect-8       117 ± 0%        76 ± 0%  -35.04%  (p=0.000 n=10+10)
```

* fix lint

* remove ignore

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

utils/markdown/autolink.go

@@ -14,6 +14,7 @@ import (
 
 var (
 	DefaultUrlSchemes = []string{"http", "https", "ftp", "mailto", "tel"}
+	wwwAutoLinkRegex  = regexp.MustCompile(`^www\d{0,3}\.`)
 )
 
 // Given a string with a w at the given position, tries to parse and return a range containing a www link.
@@ -30,7 +31,7 @@ func parseWWWAutolink(data string, position int) (Range, bool) {
 	}
 
 	// Check that this starts with www
-	if len(data)-position < 4 || !regexp.MustCompile(`^www\d{0,3}\.`).MatchString(data[position:]) {
+	if len(data)-position < 4 || !wwwAutoLinkRegex.MatchString(data[position:]) {
 		return Range{}, false
 	}
 
@@ -59,9 +60,8 @@ func isAllowedBeforeWWWLink(c byte) bool {
 	switch c {
 	case '*', '_', '~', ')':
 		return true
-	default:
-		return false
 	}
+	return false
 }
 
 // Given a string with a : at the given position, tried to parse and return a range containing a URL scheme
@@ -153,9 +153,8 @@ func checkDomain(data string, allowShort bool) int {
 	// this is called from parseWWWAutolink
 	if foundPeriod {
 		return i
-	} else {
-		return 0
 	}
+	return 0
 }
 
 // Returns true if the provided link starts with a valid character for a domain name. Equivalent to
@@ -251,7 +250,6 @@ func canEndAutolink(c rune) bool {
 	switch c {
 	case '?', '!', '.', ',', ':', '*', '_', '~', '\'', '"':
 		return false
-	default:
-		return true
 	}
+	return true
 }

utils/markdown/blocks.go

@@ -37,13 +37,14 @@ type Range struct {
 	End      int
 }
 
-func closeBlocks(blocks []Block, referenceDefinitions *[]*ReferenceDefinition) {
+func closeBlocks(blocks []Block, referenceDefinitions []*ReferenceDefinition) []*ReferenceDefinition {
 	for _, block := range blocks {
 		block.Close()
 		if p, ok := block.(*Paragraph); ok && len(p.ReferenceDefinitions) > 0 {
-			*referenceDefinitions = append(*referenceDefinitions, p.ReferenceDefinitions...)
+			referenceDefinitions = append(referenceDefinitions, p.ReferenceDefinitions...)
 		}
 	}
+	return referenceDefinitions
 }
 
 func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefinition) {
@@ -78,7 +79,7 @@ func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefiniti
 				for i := lastMatchIndex; i >= 0; i-- {
 					if container, ok := openBlocks[i].(ContainerBlock); ok {
 						if addedBlocks := container.AddChild(newBlocks); addedBlocks != nil {
-							closeBlocks(openBlocks[i+1:], &referenceDefinitions)
+							referenceDefinitions = closeBlocks(openBlocks[i+1:], referenceDefinitions)
 							openBlocks = openBlocks[:i+1]
 							openBlocks = append(openBlocks, addedBlocks...)
 							didAdd = true
@@ -98,7 +99,7 @@ func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefiniti
 			continue
 		}
 
-		closeBlocks(openBlocks[lastMatchIndex+1:], &referenceDefinitions)
+		referenceDefinitions = closeBlocks(openBlocks[lastMatchIndex+1:], referenceDefinitions)
 		openBlocks = openBlocks[:lastMatchIndex+1]
 
 		if openBlocks[lastMatchIndex].AddLine(indentation, r) {
@@ -109,7 +110,7 @@ func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefiniti
 			for i := lastMatchIndex; i >= 0; i-- {
 				if container, ok := openBlocks[i].(ContainerBlock); ok {
 					if newBlocks := container.AddChild([]Block{paragraph}); newBlocks != nil {
-						closeBlocks(openBlocks[i+1:], &referenceDefinitions)
+						referenceDefinitions = closeBlocks(openBlocks[i+1:], referenceDefinitions)
 						openBlocks = openBlocks[:i+1]
 						openBlocks = append(openBlocks, newBlocks...)
 						break
@@ -119,7 +120,7 @@ func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefiniti
 		}
 	}
 
-	closeBlocks(openBlocks, &referenceDefinitions)
+	referenceDefinitions = closeBlocks(openBlocks, referenceDefinitions)
 
 	return document, referenceDefinitions
 }

utils/markdown/inlines.go

@@ -595,7 +595,7 @@ func ParseInlines(markdown string, ranges []Range, referenceDefinitions []*Refer
 }
 
 func MergeInlineText(inlines []Inline) []Inline {
-	var ret []Inline
+	ret := inlines[:0]
 	for i, v := range inlines {
 		// always add first node
 		if i == 0 {

utils/markdown/inspect_test.go

@@ -52,3 +52,24 @@ func TestInspect(t *testing.T) {
 		"                Text",
 	}, visited)
 }
+
+var counterSink int
+
+func BenchmarkInspect(b *testing.B) {
+	text := `Some standard piece of text.
+
+Has a link [post](https://github.com) and also has a blockquote.
+
+> This is a famous quote.
+
+Some bold text **Text for markdown?** to go with it.
+
+At the end, some more lines`
+
+	for i := 0; i < b.N; i++ {
+		Inspect(text, func(_ interface{}) bool {
+			counterSink++
+			return true
+		})
+	}
+}

utils/markdown/lines.go

@@ -3,13 +3,16 @@
 
 package markdown
 
+import "strings"
+
 type Line struct {
 	Range
 }
 
-func ParseLines(markdown string) (lines []Line) {
+func ParseLines(markdown string) []Line {
 	lineStartPosition := 0
 	isAfterCarriageReturn := false
+	lines := make([]Line, 0, strings.Count(markdown, "\n"))
 	for position, r := range markdown {
 		if r == '\n' {
 			lines = append(lines, Line{Range{lineStartPosition, position + 1}})
@@ -23,5 +26,5 @@ func ParseLines(markdown string) (lines []Line) {
 	if lineStartPosition < len(markdown) {
 		lines = append(lines, Line{Range{lineStartPosition, len(markdown)}})
 	}
-	return
+	return lines
 }

utils/markdown/markdown.go

@@ -23,9 +23,8 @@ func isWhitespace(c rune) bool {
 	switch c {
 	case ' ', '\t', '\n', '\u000b', '\u000c', '\r':
 		return true
-	default:
-		return false
 	}
+	return false
 }
 
 func isWhitespaceByte(c byte) bool {