Improvements to code quality and readability (#1737)

* Remove 1 unused field and 3 unused functions

unused elements fount by running
golangci-lint run --disable-all --enable unused

src/result.go:19:2: field `index` is unused (unused)
        index  int32
        ^
src/tui/light.go:716:23: func `(*LightWindow).stderr` is unused (unused)
func (w *LightWindow) stderr(str string) {
                      ^
src/terminal.go:1015:6: func `numLinesMax` is unused (unused)
func numLinesMax(str string, max int) int {
     ^
src/tui/tui.go:167:20: func `ColorPair.is24` is unused (unused)
func (p ColorPair) is24() bool {
                   ^

* Address warnings from "gosimple" linter

src/options.go:389:83: S1003: should use strings.Contains(str, ",,,") instead (gosimple)
        if str == "," || strings.HasPrefix(str, ",,") || strings.HasSuffix(str, ",,") || strings.Index(str, ",,,") >= 0 {
                                                                                         ^
src/options.go:630:18: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        executeRegexp = regexp.MustCompile(
                        ^
src/terminal.go:29:16: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        placeholder = regexp.MustCompile("\\\\?(?:{[+sf]*[0-9,-.]*}|{q}|{\\+?f?nf?})")
                      ^
src/terminal_test.go:92:10: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        regex = regexp.MustCompile("\\w+")
                ^

* Address warnings from "staticcheck" linter

src/algo/algo.go:374:2: SA4006: this value of `offset32` is never used (staticcheck)
        offset32, T := alloc32(offset32, slab, N)
        ^
src/algo/algo.go:456:2: SA4006: this value of `offset16` is never used (staticcheck)
        offset16, C := alloc16(offset16, slab, width*M)
        ^
src/tui/tui.go:119:2: SA9004: only the first constant in this group has an explicit type (staticcheck)
        colUndefined Color = -2
        ^

7 files changed, 7 insertions, 29 deletions

diff --git a/src/algo/algo.go b/src/algo/algo.go
index 2fe5c091..a627514c 100644
--- a/src/algo/algo.go
+++ b/src/algo/algo.go
@@ -371,7 +371,7 @@ func FuzzyMatchV2(caseSensitive bool, normalize bool, forward bool, input *util.
 	// The first occurrence of each character in the pattern
 	offset32, F := alloc32(offset32, slab, M)
 	// Rune array
-	offset32, T := alloc32(offset32, slab, N)
+	_, T := alloc32(offset32, slab, N)
 	input.CopyRunes(T)
 
 	// Phase 2. Calculate bonus for each point
@@ -453,7 +453,7 @@ func FuzzyMatchV2(caseSensitive bool, normalize bool, forward bool, input *util.
 	copy(H, H0[f0:lastIdx+1])
 
 	// Possible length of consecutive chunk at each position.
-	offset16, C := alloc16(offset16, slab, width*M)
+	_, C := alloc16(offset16, slab, width*M)
 	copy(C, C0[f0:lastIdx+1])
 
 	Fsub := F[1:]
diff --git a/src/options.go b/src/options.go
index c394399d..2ab3a896 100644
--- a/src/options.go
+++ b/src/options.go
@@ -386,7 +386,7 @@ func parseKeyChords(str string, message string) map[int]string {
 	}
 
 	tokens := strings.Split(str, ",")
-	if str == "," || strings.HasPrefix(str, ",,") || strings.HasSuffix(str, ",,") || strings.Index(str, ",,,") >= 0 {
+	if str == "," || strings.HasPrefix(str, ",,") || strings.HasSuffix(str, ",,") || strings.Contains(str, ",,,") {
 		tokens = append(tokens, ",")
 	}
 
@@ -628,7 +628,7 @@ func init() {
 	// Backreferences are not supported.
 	// "~!@#$%^&*;/|".each_char.map { |c| Regexp.escape(c) }.map { |c| "#{c}[^#{c}]*#{c}" }.join('|')
 	executeRegexp = regexp.MustCompile(
-		"(?si):(execute(?:-multi|-silent)?):.+|:(execute(?:-multi|-silent)?)(\\([^)]*\\)|\\[[^\\]]*\\]|~[^~]*~|![^!]*!|@[^@]*@|\\#[^\\#]*\\#|\\$[^\\$]*\\$|%[^%]*%|\\^[^\\^]*\\^|&[^&]*&|\\*[^\\*]*\\*|;[^;]*;|/[^/]*/|\\|[^\\|]*\\|)")
+		`(?si):(execute(?:-multi|-silent)?):.+|:(execute(?:-multi|-silent)?)(\([^)]*\)|\[[^\]]*\]|~[^~]*~|![^!]*!|@[^@]*@|\#[^\#]*\#|\$[^\$]*\$|%[^%]*%|\^[^\^]*\^|&[^&]*&|\*[^\*]*\*|;[^;]*;|/[^/]*/|\|[^\|]*\|)`)
 }
 
 func parseKeymap(keymap map[int][]action, str string) {
diff --git a/src/result.go b/src/result.go
index 289d83a0..be325cbb 100644
--- a/src/result.go
+++ b/src/result.go
@@ -16,7 +16,6 @@ type colorOffset struct {
 	offset [2]int32
 	color  tui.ColorPair
 	attr   tui.Attr
-	index  int32
 }
 
 type Result struct {
diff --git a/src/terminal.go b/src/terminal.go
index 3e5683c6..3c656cce 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -26,7 +26,7 @@ var placeholder *regexp.Regexp
 var activeTempFiles []string
 
 func init() {
-	placeholder = regexp.MustCompile("\\\\?(?:{[+sf]*[0-9,-.]*}|{q}|{\\+?f?nf?})")
+	placeholder = regexp.MustCompile(`\\?(?:{[+sf]*[0-9,-.]*}|{q}|{\+?f?nf?})`)
 	activeTempFiles = []string{}
 }
 
@@ -1012,19 +1012,6 @@ func (t *Terminal) printHighlighted(result Result, attr tui.Attr, col1 tui.Color
 	return displayWidth
 }
 
-func numLinesMax(str string, max int) int {
-	lines := 0
-	for lines < max {
-		idx := strings.Index(str, "\n")
-		if idx < 0 {
-			break
-		}
-		str = str[idx+1:]
-		lines++
-	}
-	return lines
-}
-
 func (t *Terminal) printPreview() {
 	if !t.hasPreviewWindow() {
 		return
diff --git a/src/terminal_test.go b/src/terminal_test.go
index 8b828af4..74dd1066 100644
--- a/src/terminal_test.go
+++ b/src/terminal_test.go
@@ -89,7 +89,7 @@ func TestReplacePlaceholder(t *testing.T) {
 	check("echo '  foo'\\''bar baz'")
 
 	// Whitespace preserving flag with regex delimiter
-	regex = regexp.MustCompile("\\w+")
+	regex = regexp.MustCompile(`\w+`)
 
 	result = replacePlaceholder("echo {s1}", true, Delimiter{regex: regex}, printsep, false, "query", items1)
 	check("echo '  '")
diff --git a/src/tui/light.go b/src/tui/light.go
index 5d3eff88..43d7efee 100644
--- a/src/tui/light.go
+++ b/src/tui/light.go
@@ -713,10 +713,6 @@ func (w *LightWindow) csi(code string) {
 	w.renderer.csi(code)
 }
 
-func (w *LightWindow) stderr(str string) {
-	w.renderer.stderr(str)
-}
-
 func (w *LightWindow) stderrInternal(str string, allowNLCR bool) {
 	w.renderer.stderrInternal(str, allowNLCR)
 }
diff --git a/src/tui/tui.go b/src/tui/tui.go
index be5bd26a..9b821940 100644
--- a/src/tui/tui.go
+++ b/src/tui/tui.go
@@ -117,7 +117,7 @@ func (c Color) is24() bool {
 
 const (
 	colUndefined Color = -2
-	colDefault         = -1
+	colDefault   Color = -1
 )
 
 const (
@@ -164,10 +164,6 @@ func (p ColorPair) Bg() Color {
 	return p.bg
 }
 
-func (p ColorPair) is24() bool {
-	return p.fg.is24() || p.bg.is24()
-}
-
 type ColorTheme struct {
 	Fg           Color
 	Bg           Color