cmd/shfmt: add a -fn printer option

This option allows placing a function's opening brace on a separate line,
which brings one's style a bit closer to K&R. It can also be useful to quickly
find or jump to function definitions.

The same option is exposed in the syntax package.

Fixes #229.

cmd/shfmt/main.go

@@ -38,11 +38,12 @@ var (
 	langStr = flag.String("ln", "", "")
 	posix   = flag.Bool("p", false, "")
 
-	indent      = flag.Uint("i", 0, "")
-	binNext     = flag.Bool("bn", false, "")
-	caseIndent  = flag.Bool("ci", false, "")
-	spaceRedirs = flag.Bool("sr", false, "")
-	keepPadding = flag.Bool("kp", false, "")
+	indent          = flag.Uint("i", 0, "")
+	binNext         = flag.Bool("bn", false, "")
+	caseIndent      = flag.Bool("ci", false, "")
+	spaceRedirs     = flag.Bool("sr", false, "")
+	keepPadding     = flag.Bool("kp", false, "")
+	functionNewLine = flag.Bool("fn", false, "")
 
 	toJSON = flag.Bool("tojson", false, "")
 
@@ -91,6 +92,7 @@ Printer options:
   -ci       switch cases will be indented
   -sr       redirect operators will be followed by a space
   -kp       keep column alignment paddings
+  -fn       function opening braces are placed on a separate line
 
 Utilities:
 
@@ -116,7 +118,7 @@ Utilities:
 	}
 	flag.Visit(func(f *flag.Flag) {
 		switch f.Name {
-		case "ln", "p", "i", "bn", "ci", "sr", "kp":
+		case "ln", "p", "i", "bn", "ci", "sr", "kp", "fn":
 			useEditorConfig = false
 		}
 	})
@@ -145,6 +147,7 @@ Utilities:
 		syntax.SwitchCaseIndent(*caseIndent)(printer)
 		syntax.SpaceRedirects(*spaceRedirs)(printer)
 		syntax.KeepPadding(*keepPadding)(printer)
+		syntax.FunctionNewLine(*functionNewLine)(printer)
 	}
 
 	if os.Getenv("FORCE_COLOR") == "true" {

syntax/printer.go

@@ -68,6 +68,11 @@ func Minify(enabled bool) PrinterOption {
 	return func(p *Printer) { p.minify = enabled }
 }
 
+// FunctionNewLine will place function braces on a new line.
+func FunctionNewLine(enabled bool) PrinterOption {
+	return func(p *Printer) { p.functionNewLine = enabled }
+}
+
 // NewPrinter allocates a new Printer and applies any number of options.
 func NewPrinter(opts ...PrinterOption) *Printer {
 	p := &Printer{
@@ -188,12 +193,13 @@ type Printer struct {
 	tabWriter *tabwriter.Writer
 	cols      colCounter
 
-	indentSpaces   uint
-	binNextLine    bool
-	swtCaseIndent  bool
-	spaceRedirects bool
-	keepPadding    bool
-	minify         bool
+	indentSpaces    uint
+	binNextLine     bool
+	swtCaseIndent   bool
+	spaceRedirects  bool
+	keepPadding     bool
+	minify          bool
+	functionNewLine bool
 
 	wantSpace   bool
 	wantNewline bool
@@ -962,6 +968,8 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 	case *Block:
 		p.WriteByte('{')
 		p.wantSpace = true
+		// Forbid "foo()\n{ bar; }"
+		p.wantNewline = p.wantNewline || p.functionNewLine
 		p.nestedStmts(x.Stmts, x.Last, x.Rbrace)
 		p.semiRsrv("}", x.Rbrace)
 	case *IfClause:
@@ -1040,7 +1048,9 @@ func (p *Printer) command(cmd Command, redirs []*Redirect) (startRedirs int) {
 		}
 		p.writeLit(x.Name.Value)
 		p.WriteString("()")
-		if !p.minify {
+		if p.functionNewLine {
+			p.newline(Pos{})
+		} else if !p.minify {
 			p.space()
 		}
 		p.line = x.Body.Pos().Line()

syntax/printer_test.go

@@ -743,6 +743,35 @@ func TestPrintSwitchCaseIndent(t *testing.T) {
 	}
 }
 
+func TestPrintFunctionNewLine(t *testing.T) {
+	t.Parallel()
+	tests := [...]printCase{
+		{
+			"foo() { bar; }",
+			"foo()\n{\n\tbar\n}",
+		},
+		{
+			"foo()\n{ bar; }",
+			"foo()\n{\n\tbar\n}",
+		},
+		{
+			"foo()\n\n{\n\n\tbar\n}",
+			"foo()\n{\n\n\tbar\n}",
+		},
+		{
+			"function foo {\n\tbar\n}",
+			"function foo()\n{\n\tbar\n}",
+		},
+	}
+	parser := NewParser(KeepComments(true))
+	printer := NewPrinter(FunctionNewLine(true))
+	for i, tc := range tests {
+		t.Run(fmt.Sprintf("%03d", i), func(t *testing.T) {
+			printTest(t, parser, printer, tc.in, tc.want)
+		})
+	}
+}
+
 func TestPrintSpaceRedirects(t *testing.T) {
 	t.Parallel()
 	tests := [...]printCase{