perf: fix 34 self-detected performance issues

fixer/fixer.go

@@ -82,10 +82,11 @@ func validatePathForWrite(filename string) error {
 
 // FixIssues attempts to fix the given issues
 func (f *Fixer) FixIssues(issues []rules.Issue) []Fix {
-	var fixes []Fix
+	// Preallocate: assume ~1 fix per issue
+	fixes := make([]Fix, 0, len(issues))
 
-	// Group issues by file
-	byFile := make(map[string][]rules.Issue)
+	// Group issues by file with size hint
+	byFile := make(map[string][]rules.Issue, len(issues)/2+1)
 	for _, issue := range issues {
 		byFile[issue.File] = append(byFile[issue.File], issue)
 	}
@@ -99,7 +100,7 @@ func (f *Fixer) FixIssues(issues []rules.Issue) []Fix {
 }
 
 func (f *Fixer) fixFile(filename string, issues []rules.Issue) []Fix {
-	var fixes []Fix
+	fixes := make([]Fix, 0, len(issues))
 
 	// Validate path before any operations
 	if err := validatePathForWrite(filename); err != nil {

main.go

@@ -109,8 +109,8 @@
 		Verbose:     *verboseFlag,
 	})
 
-	// Collect Go files
-	var files []string
+	// Collect Go files - estimate ~100 files per pattern
+	files := make([]string, 0, len(paths)*100)
 	for _, pattern := range paths {
 		matches, err := collectGoFiles(pattern, ignorePaths)
 		if err != nil {
@@ -236,7 +236,8 @@
 }
 
 func collectGoFiles(pattern string, ignorePaths []string) ([]string, error) {
-	var files []string
+	// Preallocate with reasonable estimate
+	files := make([]string, 0, 64)
 	fileCount := 0
 
 	// Validate the base pattern first
@@ -361,7 +362,7 @@
 	Low      int `json:"low"`
 }
 
 func toJSON(issues []rules.Issue) string {
 	summary := Summary{Total: len(issues)}
 	for _, issue := range issues {
 		switch issue.Severity {

reporter/console.go

@@ -176,7 +176,9 @@ func wordWrap(text string, width int, indent string) string {
 		return text
 	}
 
-	var lines []string
+	// Estimate lines needed: text length / width
+	estimatedLines := len(text)/width + 1
+	lines := make([]string, 0, estimatedLines)
 	var currentLine strings.Builder
 
 	for _, word := range words {

rules/algorithm.go

@@ -18,7 +18,7 @@ func (r *NestedRangeRule) Name() string     { return "nested-range" }
 func (r *NestedRangeRule) Category() string { return "algorithm" }
 
 func (r *NestedRangeRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		funcDecl, ok := n.(*ast.FuncDecl)
@@ -187,7 +187,7 @@ func (r *LinearSearchInLoopRule) Name() string     { return "linear-search-in-lo
 func (r *LinearSearchInLoopRule) Category() string { return "algorithm" }
 
 func (r *LinearSearchInLoopRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		funcDecl, ok := n.(*ast.FuncDecl)

rules/allocation.go

@@ -19,7 +19,7 @@ func (r *UnpreallocatedSliceRule) Name() string     { return "unpreallocated-sli
 func (r *UnpreallocatedSliceRule) Category() string { return "allocation" }
 
 func (r *UnpreallocatedSliceRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 8)
 
 	// For each function, track preallocated slices
 	ast.Inspect(file, func(n ast.Node) bool {
@@ -186,7 +186,7 @@ func (r *StringConcatInLoopRule) Name() string     { return "string-concat-loop"
 func (r *StringConcatInLoopRule) Category() string { return "allocation" }
 
 func (r *StringConcatInLoopRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Track strings.Builder usage
 	builders := findStringBuilders(file)
@@ -320,7 +320,7 @@ func (r *MapWithoutSizeRule) Name() string     { return "map-without-size" }
 func (r *MapWithoutSizeRule) Category() string { return "allocation" }
 
 func (r *MapWithoutSizeRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Only flag maps that are actually populated in loops
 	ast.Inspect(file, func(n ast.Node) bool {

rules/analyzer.go

@@ -16,7 +16,12 @@ type Analyzer struct {
 
 // NewAnalyzer creates a new analyzer with the given config
 func NewAnalyzer(config AnalyzerConfig) *Analyzer {
-	a := &Analyzer{config: config}
+	// Estimate total rules: ~3 rules per category on average
+	estimatedRules := len(config.Rules) * 3
+	a := &Analyzer{
+		config: config,
+		rules:  make([]Rule, 0, estimatedRules),
+	}
 
 	// Collect rules based on config
 	for _, category := range config.Rules {
@@ -30,7 +35,8 @@ func NewAnalyzer(config AnalyzerConfig) *Analyzer {
 
 // Analyze runs all rules against the given files
 func (a *Analyzer) Analyze(files []string) []Issue {
-	var allIssues []Issue
+	// Preallocate with estimate: ~2 issues per file on average
+	allIssues := make([]Issue, 0, len(files)*2)
 
 	fset := token.NewFileSet()
 
@@ -90,7 +96,7 @@ func (a *Analyzer) Analyze(files []string) []Issue {
 
 // FindNestedRangeLoops finds nested for-range loops
 func FindNestedRangeLoops(file *ast.File, fset *token.FileSet) []ast.Node {
-	var nested []ast.Node
+	nested := make([]ast.Node, 0, 4) // Most files have few nested loops
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		outerRange, ok := n.(*ast.RangeStmt)
@@ -116,7 +122,7 @@ func FindNestedRangeLoops(file *ast.File, fset *token.FileSet) []ast.Node {
 
 // FindAppendInLoop finds append calls inside loops without preallocation
 func FindAppendInLoop(file *ast.File, fset *token.FileSet) []AppendInLoopInfo {
-	var results []AppendInLoopInfo
+	results := make([]AppendInLoopInfo, 0, 8) // Typical file has few append-in-loop issues
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		// Look for for statements (both range and regular)
@@ -174,7 +180,7 @@ type AppendInLoopInfo struct {
 
 // FindStringConcatInLoop finds string concatenation in loops
 func FindStringConcatInLoop(file *ast.File, fset *token.FileSet) []token.Position {
-	var results []token.Position
+	results := make([]token.Position, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		var loopBody *ast.BlockStmt
@@ -215,7 +221,7 @@ func FindStringConcatInLoop(file *ast.File, fset *token.FileSet) []token.Positio
 
 // FindSQLInLoop finds database query patterns inside loops
 func FindSQLInLoop(file *ast.File, fset *token.FileSet) []SQLInLoopInfo {
-	var results []SQLInLoopInfo
+	results := make([]SQLInLoopInfo, 0, 4)
 
 	sqlMethods := map[string]bool{
 		"Query":      true,
@@ -277,7 +283,7 @@ type SQLInLoopInfo struct {
 
 // FindUnbufferedChannels finds unbuffered channel creation
 func FindUnbufferedChannels(file *ast.File, fset *token.FileSet) []token.Position {
-	var results []token.Position
+	results := make([]token.Position, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		call, ok := n.(*ast.CallExpr)
@@ -347,7 +353,7 @@ func FindMutexHotspots(file *ast.File, fset *token.FileSet) map[string]int {
 
 // FindJSONInLoop finds JSON marshal/unmarshal calls in loops
 func FindJSONInLoop(file *ast.File, fset *token.FileSet) []JSONInLoopInfo {
-	var results []JSONInLoopInfo
+	results := make([]JSONInLoopInfo, 0, 4)
 
 	jsonFuncs := map[string]bool{
 		"Marshal":   true,

rules/benchmark.go

@@ -3,6 +3,7 @@ package rules
 import (
 	"go/ast"
 	"go/token"
+	"strings"
 )
 
 func init() {
@@ -132,33 +133,40 @@ func generateBenchmarkCode(funcName string, funcDecl *ast.FuncDecl) string {
 	// Generate basic benchmark scaffold
 	benchName := "Benchmark" + capitalizeFirst(funcName)
 
-	code := "func " + benchName + "(b *testing.B) {\n"
-	code += "\t// Setup: initialize test data\n"
+	var b strings.Builder
+	b.Grow(256) // Pre-allocate reasonable capacity
+
+	b.WriteString("func ")
+	b.WriteString(benchName)
+	b.WriteString("(b *testing.B) {\n")
+	b.WriteString("\t// Setup: initialize test data\n")
 
 	// Add parameter hints based on function signature
 	if funcDecl.Type.Params != nil && len(funcDecl.Type.Params.List) > 0 {
-		code += "\t// params: "
+		b.WriteString("\t// params: ")
 		for i, param := range funcDecl.Type.Params.List {
 			if i > 0 {
-				code += ", "
+				b.WriteString(", ")
 			}
 			for j, name := range param.Names {
 				if j > 0 {
-					code += ", "
+					b.WriteString(", ")
 				}
-				code += name.Name
+				b.WriteString(name.Name)
 			}
 		}
-		code += "\n"
+		b.WriteString("\n")
 	}
 
-	code += "\n\tb.ResetTimer()\n"
-	code += "\tfor i := 0; i < b.N; i++ {\n"
-	code += "\t\t" + funcName + "(...) // Add arguments\n"
-	code += "\t}\n"
-	code += "}"
+	b.WriteString("\n\tb.ResetTimer()\n")
+	b.WriteString("\tfor i := 0; i < b.N; i++ {\n")
+	b.WriteString("\t\t")
+	b.WriteString(funcName)
+	b.WriteString("(...) // Add arguments\n")
+	b.WriteString("\t}\n")
+	b.WriteString("}")
 
-	return code
+	return b.String()
 }
 
 func capitalizeFirst(s string) string {
@@ -177,12 +185,15 @@ func joinPatterns(patterns []perfPattern) string {
 		return ""
 	}
 
-	result := ""
+	var b strings.Builder
+	b.Grow(len(patterns) * 20) // Estimate ~20 chars per pattern
 	for i, p := range patterns {
 		if i > 0 {
-			result += ", "
+			b.WriteString(", ")
 		}
-		result += itoa(p.count) + " " + p.name
+		b.WriteString(itoa(p.count))
+		b.WriteString(" ")
+		b.WriteString(p.name)
 	}
-	return result
+	return b.String()
 }

rules/cache.go

@@ -19,7 +19,7 @@ func (r *RepeatedRegexpCompileRule) Name() string     { return "repeated-regexp-
 func (r *RepeatedRegexpCompileRule) Category() string { return "cache" }
 
 func (r *RepeatedRegexpCompileRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Track if we're inside a function
 	var inFunc bool
@@ -75,7 +75,7 @@ func (r *RepeatedTemplateParseRule) Name() string     { return "repeated-templat
 func (r *RepeatedTemplateParseRule) Category() string { return "cache" }
 
 func (r *RepeatedTemplateParseRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	var inFunc bool
 
@@ -134,7 +134,7 @@ func (r *RegexpMatchStringRule) Name() string     { return "regexp-match-string-
 func (r *RegexpMatchStringRule) Category() string { return "cache" }
 
 func (r *RegexpMatchStringRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		var loopBody *ast.BlockStmt
@@ -202,7 +202,7 @@ func (r *JSONSchemaValidationRule) Name() string     { return "json-schema-in-lo
 func (r *JSONSchemaValidationRule) Category() string { return "cache" }
 
 func (r *JSONSchemaValidationRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		var loopBody *ast.BlockStmt

rules/concurrency.go

@@ -19,7 +19,7 @@ func (r *UnbufferedChannelRule) Name() string     { return "unbuffered-channel"
 func (r *UnbufferedChannelRule) Category() string { return "concurrency" }
 
 func (r *UnbufferedChannelRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		funcDecl, ok := n.(*ast.FuncDecl)
@@ -273,7 +273,7 @@ func (r *MutexInLoopRule) Name() string     { return "mutex-in-loop" }
 func (r *MutexInLoopRule) Category() string { return "concurrency" }
 
 func (r *MutexInLoopRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		var loopBody *ast.BlockStmt
@@ -343,7 +343,7 @@ func (r *GoroutineLeakRule) Name() string     { return "goroutine-leak" }
 func (r *GoroutineLeakRule) Category() string { return "concurrency" }
 
 func (r *GoroutineLeakRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		goStmt, ok := n.(*ast.GoStmt)

rules/context.go

@@ -18,7 +18,7 @@
 func (r *ContextBackgroundInHandlerRule) Category() string { return "context" }
 
 func (r *ContextBackgroundInHandlerRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		funcDecl, ok := n.(*ast.FuncDecl)
@@ -82,7 +82,7 @@
 func (r *MissingContextTimeoutRule) Category() string { return "context" }
 
 func (r *MissingContextTimeoutRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Track contexts with timeouts in each function
 	ast.Inspect(file, func(n ast.Node) bool {
@@ -151,7 +151,7 @@
 				}
 
 				// For Do, Get, etc. - check if context seems to have timeout
 				if !hasTimeoutCtx && (sel.Sel.Name == "Do" || sel.Sel.Name == "Get" || sel.Sel.Name == "Invoke") {
 					// This is a heuristic - we can't be 100% sure without type info
 					// Only flag if the receiver looks like an HTTP client
 				}
@@ -173,7 +173,7 @@
 func (r *ContextLeakRule) Category() string { return "context" }
 
 func (r *ContextLeakRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		funcDecl, ok := n.(*ast.FuncDecl)

rules/database.go

@@ -17,7 +17,7 @@ func (r *SQLInLoopRule) Name() string     { return "sql-in-loop" }
 func (r *SQLInLoopRule) Category() string { return "database" }
 
 func (r *SQLInLoopRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Track prepared statements declared in the current scope
 	preparedStmts := findPreparedStatements(file)
@@ -255,7 +255,7 @@ func (r *UnbatchedInsertRule) Name() string     { return "unbatched-insert" }
 func (r *UnbatchedInsertRule) Category() string { return "database" }
 
 func (r *UnbatchedInsertRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		var loopBody *ast.BlockStmt

rules/dbpool.go

@@ -17,7 +17,7 @@ func (r *MissingConnectionPoolRule) Name() string     { return "missing-connecti
 func (r *MissingConnectionPoolRule) Category() string { return "database" }
 
 func (r *MissingConnectionPoolRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 4)
 
 	// Find sql.Open calls
 	sqlOpenVars := make(map[string]token.Position)
@@ -111,7 +111,7 @@ func (r *UnlimitedConnectionPoolRule) Name() string     { return "unlimited-conn
 func (r *UnlimitedConnectionPoolRule) Category() string { return "database" }
 
 func (r *UnlimitedConnectionPoolRule) Check(file *ast.File, fset *token.FileSet, src []byte) []Issue {
-	var issues []Issue
+	issues := make([]Issue, 0, 2)
 
 	ast.Inspect(file, func(n ast.Node) bool {
 		call, ok := n.(*ast.CallExpr)