feat: support multi-line function expansion based on param count

main.go

@@ -69,6 +69,12 @@ var (
 	shortenComments = kingpin.Flag(
 		"shorten-comments",
 		"Shorten single-line comments").Default("false").Bool()
+	funcParamThreshold = kingpin.Flag(
+		"func-param-threshold",
+		"Expand function signatures to one-param-per-line when they have this many or more parameters "+
+			"(0 to disable)",
+	).
+		Default("0").Int()
 	tabLen = kingpin.Flag(
 		"tab-len",
 		"Length of a tab").Short('t').Default("4").Int()
@@ -151,13 +157,14 @@ type Runner struct {
 
 func NewRunner() *Runner {
 	config := &shorten.Config{
-		MaxLen:          deref(maxLen),
-		TabLen:          deref(tabLen),
-		KeepAnnotations: deref(keepAnnotations),
-		ShortenComments: deref(shortenComments),
-		ReformatTags:    deref(reformatTags),
-		DotFile:         deref(dotFile),
-		ChainSplitDots:  deref(chainSplitDots),
+		MaxLen:             deref(maxLen),
+		TabLen:             deref(tabLen),
+		KeepAnnotations:    deref(keepAnnotations),
+		ShortenComments:    deref(shortenComments),
+		ReformatTags:       deref(reformatTags),
+		DotFile:            deref(dotFile),
+		ChainSplitDots:     deref(chainSplitDots),
+		FuncParamThreshold: deref(funcParamThreshold),
 	}
 
 	return &Runner{

shorten/format.go

@@ -51,7 +51,8 @@ func (s *Shortener) formatNode(node dst.Node) {
 func (s *Shortener) formatDecl(decl dst.Decl) {
 	switch d := decl.(type) {
 	case *dst.FuncDecl:
-		if d.Type != nil && d.Type.Params != nil && annotation.HasRecursive(d) {
+		if d.Type != nil && d.Type.Params != nil &&
+			(annotation.HasRecursive(d) || s.shouldExpandParams(d.Type.Params)) {
 			s.formatFieldList(d.Type.Params)
 		}
 
@@ -233,16 +234,21 @@ func (s *Shortener) formatExpr(expr dst.Expr, force, isChain bool) {
 		s.formatExprs(e.Elts, false, isChain)
 
 	case *dst.FuncLit:
+		if e.Type != nil && s.shouldExpandParams(e.Type.Params) {
+			s.formatFieldList(e.Type.Params)
+		}
+
 		s.formatStmt(e.Body, false)
 
 	case *dst.FuncType:
-		if shouldShorten {
+		if shouldShorten || s.shouldExpandParams(e.Params) {
 			s.formatFieldList(e.Params)
 		}
 
 	case *dst.InterfaceType:
 		for _, method := range e.Methods.List {
-			if annotation.Has(method) {
+			funcType, isFuncType := method.Type.(*dst.FuncType)
+			if annotation.Has(method) || (isFuncType && s.shouldExpandParams(funcType.Params)) {
 				s.formatExpr(method.Type, true, isChain)
 			}
 		}

shorten/shortener.go

@@ -42,6 +42,11 @@ type Config struct {
 
 	// ChainSplitDots Whether to split chain methods by putting dots at the ends of lines
 	ChainSplitDots bool
+
+	// FuncParamThreshold triggers multi-line expansion of function signatures
+	// with this many or more parameters, regardless of line length.
+	// Set to 0 (default) to disable.
+	FuncParamThreshold int
 }
 
 // NewDefaultConfig returns a [Config] with default values.
@@ -186,10 +191,34 @@ func (s *Shortener) Process(content []byte) ([]byte, error) {
 // if there are lines to shorten,
 // or if this is the first round (0),
 // and the option to reformat struct tags is enabled,
-// and there are struct tags with multiple entries.
+// and there are struct tags with multiple entries,
+// or if this is the first round (0),
+// and func param threshold expansion is enabled.
 func (s *Shortener) shouldContinue(nbLinesToShorten, round int, lines []string) bool {
 	return nbLinesToShorten > 0 ||
-		round == 0 && s.config.ReformatTags && tags.HasMultipleEntries(lines)
+		round == 0 && s.config.ReformatTags && tags.HasMultipleEntries(lines) ||
+		round == 0 && s.config.FuncParamThreshold > 0
+}
+
+// shouldExpandParams reports whether a field list has enough parameters
+// to trigger multi-line expansion based on the configured threshold.
+// Named parameters with shared types (e.g. a, b int) count individually.
+func (s *Shortener) shouldExpandParams(params *dst.FieldList) bool {
+	if s.config.FuncParamThreshold <= 0 || params == nil {
+		return false
+	}
+
+	count := 0
+
+	for _, field := range params.List {
+		if len(field.Names) == 0 {
+			count++ // unnamed parameter: func(int, string)
+		} else {
+			count += len(field.Names) // named: func(a, b int) counts as 2
+		}
+	}
+
+	return count >= s.config.FuncParamThreshold
 }
 
 func (s *Shortener) createDot(result dst.Node) error {

shorten/testdata/func_param_threshold/func_param_threshold.go

@@ -0,0 +1,106 @@
+package fixtures
+
+// Functions below threshold: unchanged.
+
+func zeroParams() error {
+	return nil
+}
+
+func oneParam(a int) error {
+	return nil
+}
+
+func twoParams(a int, b string) error {
+	return nil
+}
+
+// Functions at or above threshold: expand.
+
+func threeParams(a int, b string, c bool) error {
+	return nil
+}
+
+func fourParams(a int, b string, c bool, d float64) error {
+	return nil
+}
+
+// Methods: receiver is not counted toward the threshold.
+
+type Receiver struct{}
+
+func (r *Receiver) methodTwoParams(a int, b string) error {
+	return nil
+}
+
+func (r *Receiver) methodThreeParams(a int, b string, c bool) error {
+	return nil
+}
+
+// Value receiver on a named basic type: receiver still not counted.
+
+type MyString string
+
+func (s MyString) basicTypeTwoParams(a int, b string) error {
+	return nil
+}
+
+func (s MyString) basicTypeThreeParams(a int, b string, c bool) error {
+	return nil
+}
+
+// Named params with shared types: count names, not fields.
+// a, b int, c string = 3 logical params.
+
+func sharedTypes(a, b int, c string) error {
+	return nil
+}
+
+// Unnamed params.
+
+func unnamed(int, string, bool) error {
+	return nil
+}
+
+// Variadic: a + b = 2 logical params, unchanged.
+
+func variadic(a int, b ...string) error {
+	return nil
+}
+
+// Already multi-line: idempotent, no change.
+
+func alreadyMultiLine(
+	a int,
+	b string,
+	c bool,
+) error {
+	return nil
+}
+
+// Return values are not counted toward the threshold.
+
+func returnValuesNotCounted(a int) (int, string, bool) {
+	return 0, "", false
+}
+
+// Interface methods.
+
+type MyInterface interface {
+	interfaceMethodTwo(a int, b string) error
+	interfaceMethodThree(a int, b string, c bool) error
+}
+
+// Function type declarations.
+
+type MyFunc func(a int, b string, c bool) error
+
+// Function literals.
+
+func funcLiterals() {
+	_ = func(a int, b string) error {
+		return nil
+	}
+	_ = func(a int, b string, c bool) error {
+		return nil
+	}
+}

shorten/testdata/func_param_threshold/func_param_threshold.go.golden

@@ -0,0 +1,142 @@
+package fixtures
+
+// Functions below threshold: unchanged.
+
+func zeroParams() error {
+	return nil
+}
+
+func oneParam(a int) error {
+	return nil
+}
+
+func twoParams(a int, b string) error {
+	return nil
+}
+
+// Functions at or above threshold: expand.
+
+func threeParams(
+	a int,
+	b string,
+	c bool,
+) error {
+	return nil
+}
+
+func fourParams(
+	a int,
+	b string,
+	c bool,
+	d float64,
+) error {
+	return nil
+}
+
+// Methods: receiver is not counted toward the threshold.
+
+type Receiver struct{}
+
+func (r *Receiver) methodTwoParams(a int, b string) error {
+	return nil
+}
+
+func (r *Receiver) methodThreeParams(
+	a int,
+	b string,
+	c bool,
+) error {
+	return nil
+}
+
+// Value receiver on a named basic type: receiver still not counted.
+
+type MyString string
+
+func (s MyString) basicTypeTwoParams(a int, b string) error {
+	return nil
+}
+
+func (s MyString) basicTypeThreeParams(
+	a int,
+	b string,
+	c bool,
+) error {
+	return nil
+}
+
+// Named params with shared types: count names, not fields.
+// a, b int, c string = 3 logical params.
+
+func sharedTypes(
+	a, b int,
+	c string,
+) error {
+	return nil
+}
+
+// Unnamed params.
+
+func unnamed(
+	int,
+	string,
+	bool,
+) error {
+	return nil
+}
+
+// Variadic: a + b = 2 logical params, unchanged.
+
+func variadic(a int, b ...string) error {
+	return nil
+}
+
+// Already multi-line: idempotent, no change.
+
+func alreadyMultiLine(
+	a int,
+	b string,
+	c bool,
+) error {
+	return nil
+}
+
+// Return values are not counted toward the threshold.
+
+func returnValuesNotCounted(a int) (int, string, bool) {
+	return 0, "", false
+}
+
+// Interface methods.
+
+type MyInterface interface {
+	interfaceMethodTwo(a int, b string) error
+	interfaceMethodThree(
+		a int,
+		b string,
+		c bool,
+	) error
+}
+
+// Function type declarations.
+
+type MyFunc func(
+	a int,
+	b string,
+	c bool,
+) error
+
+// Function literals.
+
+func funcLiterals() {
+	_ = func(a int, b string) error {
+		return nil
+	}
+	_ = func(
+		a int,
+		b string,
+		c bool,
+	) error {
+		return nil
+	}
+}

shorten/testdata/func_param_threshold/func_param_threshold.json

@@ -0,0 +1,9 @@
+{
+  "MaxLen": 100,
+  "TabLen": 4,
+  "KeepAnnotations": false,
+  "ShortenComments": false,
+  "ReformatTags": true,
+  "ChainSplitDots": true,
+  "FuncParamThreshold": 3
+}

shorten/testdata/func_param_threshold_disabled/func_param_threshold_disabled.go

@@ -0,0 +1,13 @@
+package fixtures
+
+func threeParams(a int, b string, c bool) error {
+	return nil
+}
+
+func fourParams(a int, b string, c bool, d float64) error {
+	return nil
+}
+
+func fiveParams(a int, b string, c bool, d float64, e []byte) error {
+	return nil
+}