go/printer: Permit declaration and statement lists as input.

Also: Can set base indentation in printer.Config: all code
is going to be indented by at least that amount (except for
raw string literals spanning multiple lines, since their
values must not change).

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6847086

src/pkg/go/printer/nodes.go

@@ -900,7 +900,11 @@ func (p *printer) stmtList(list []ast.Stmt, nindent int, nextIsRBrace bool) {
 		if _, isEmpty := s.(*ast.EmptyStmt); !isEmpty {
 			// _indent == 0 only for lists of switch/select case clauses;
 			// in those cases each clause is a new section
+			if len(p.output) > 0 {
+				// only print line break if we are not at the beginning of the output
+				// (i.e., we are not printing only a partial program)
 				p.linebreak(p.lineFor(s.Pos()), 1, ignore, i == 0 || nindent == 0 || multiLine)
+			}
 			p.stmt(s, nextIsRBrace && i == len(list)-1)
 			multiLine = p.isMultiLine(s)
 			i++
@@ -1523,31 +1527,35 @@ func declToken(decl ast.Decl) (tok token.Token) {
 	return
 }
 
-func (p *printer) file(src *ast.File) {
-	p.setComment(src.Doc)
-	p.print(src.Pos(), token.PACKAGE, blank)
-	p.expr(src.Name)
-
-	if len(src.Decls) > 0 {
+func (p *printer) declList(list []ast.Decl) {
 	tok := token.ILLEGAL
-		for _, d := range src.Decls {
+	for _, d := range list {
 		prev := tok
 		tok = declToken(d)
-			// if the declaration token changed (e.g., from CONST to TYPE)
+		// If the declaration token changed (e.g., from CONST to TYPE)
 		// or the next declaration has documentation associated with it,
-			// print an empty line between top-level declarations
+		// print an empty line between top-level declarations.
 		// (because p.linebreak is called with the position of d, which
 		// is past any documentation, the minimum requirement is satisfied
 		// even w/o the extra getDoc(d) nil-check - leave it in case the
 		// linebreak logic improves - there's already a TODO).
+		if len(p.output) > 0 {
+			// only print line break if we are not at the beginning of the output
+			// (i.e., we are not printing only a partial program)
 			min := 1
 			if prev != tok || getDoc(d) != nil {
 				min = 2
 			}
 			p.linebreak(p.lineFor(d.Pos()), min, ignore, false)
-			p.decl(d)
 		}
+		p.decl(d)
 	}
+}
 
+func (p *printer) file(src *ast.File) {
+	p.setComment(src.Doc)
+	p.print(src.Pos(), token.PACKAGE, blank)
+	p.expr(src.Name)
+	p.declList(src.Decls)
 	p.print(newline)
 }

src/pkg/go/printer/performance_test.go

@@ -20,7 +20,7 @@ import (
 var testfile *ast.File
 
 func testprint(out io.Writer, file *ast.File) {
-	if err := (&Config{TabIndent | UseSpaces, 8}).Fprint(out, fset, file); err != nil {
+	if err := (&Config{TabIndent | UseSpaces, 8, 0}).Fprint(out, fset, file); err != nil {
 		log.Fatalf("print error: %s", err)
 	}
 }

src/pkg/go/printer/printer.go

@@ -165,15 +165,15 @@ func (p *printer) atLineBegin(pos token.Position) {
 	// write indentation
 	// use "hard" htabs - indentation columns
 	// must not be discarded by the tabwriter
-	for i := 0; i < p.indent; i++ {
+	n := p.Config.Indent + p.indent // include base indentation
+	for i := 0; i < n; i++ {
 		p.output = append(p.output, '\t')
 	}
 
 	// update positions
-	i := p.indent
-	p.pos.Offset += i
-	p.pos.Column += i
-	p.out.Column += i
+	p.pos.Offset += n
+	p.pos.Column += n
+	p.out.Column += n
 }
 
 // writeByte writes ch n times to p.output and updates p.pos.
@@ -1032,9 +1032,9 @@ func (p *printer) printNode(node interface{}) error {
 	case ast.Expr:
 		p.expr(n)
 	case ast.Stmt:
-		// A labeled statement will un-indent to position the
-		// label. Set indent to 1 so we don't get indent "underflow".
-		if _, labeledStmt := n.(*ast.LabeledStmt); labeledStmt {
+		// A labeled statement will un-indent to position the label.
+		// Set p.indent to 1 so we don't get indent "underflow".
+		if _, ok := n.(*ast.LabeledStmt); ok {
 			p.indent = 1
 		}
 		p.stmt(n, false)
@@ -1042,6 +1042,17 @@ func (p *printer) printNode(node interface{}) error {
 		p.decl(n)
 	case ast.Spec:
 		p.spec(n, 1, false)
+	case []ast.Stmt:
+		// A labeled statement will un-indent to position the label.
+		// Set p.indent to 1 so we don't get indent "underflow".
+		for _, s := range n {
+			if _, ok := s.(*ast.LabeledStmt); ok {
+				p.indent = 1
+			}
+		}
+		p.stmtList(n, 0, false)
+	case []ast.Decl:
+		p.declList(n)
 	case *ast.File:
 		p.file(n)
 	default:
@@ -1174,6 +1185,7 @@ const (
 type Config struct {
 	Mode     Mode // default: 0
 	Tabwidth int  // default: 8
+	Indent   int  // default: 0 (all code is indented at least by this much)
 }
 
 // fprint implements Fprint and takes a nodesSizes map for setting up the printer state.
@@ -1235,8 +1247,8 @@ type CommentedNode struct {
 
 // Fprint "pretty-prints" an AST node to output for a given configuration cfg.
 // Position information is interpreted relative to the file set fset.
-// The node type must be *ast.File, *CommentedNode, or assignment-compatible
-// to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.
+// The node type must be *ast.File, *CommentedNode, []ast.Decl, []ast.Stmt,
+// or assignment-compatible to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.
 //
 func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) error {
 	return cfg.fprint(output, fset, node, make(map[ast.Node]int))

src/pkg/go/printer/printer_test.go

@@ -434,6 +434,98 @@ func (t *t) foo(a, b, c int) int {
 	}
 }
 
+var decls = []string{
+	`import "fmt"`,
+	"const pi = 3.1415\nconst e = 2.71828\n\nvar x = pi",
+	"func sum(x, y int) int\t{ return x + y }",
+}
+
+func TestDeclLists(t *testing.T) {
+	for _, src := range decls {
+		file, err := parser.ParseFile(fset, "", "package p;"+src, parser.ParseComments)
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		var buf bytes.Buffer
+		err = Fprint(&buf, fset, file.Decls) // only print declarations
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		out := buf.String()
+		if out != src {
+			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
+		}
+	}
+}
+
+var stmts = []string{
+	"i := 0",
+	"select {}\nvar a, b = 1, 2\nreturn a + b",
+	"go f()\ndefer func() {}()",
+}
+
+func TestStmtLists(t *testing.T) {
+	for _, src := range stmts {
+		file, err := parser.ParseFile(fset, "", "package p; func _() {"+src+"}", parser.ParseComments)
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		var buf bytes.Buffer
+		err = Fprint(&buf, fset, file.Decls[0].(*ast.FuncDecl).Body.List) // only print statements
+		if err != nil {
+			panic(err) // error in test
+		}
+
+		out := buf.String()
+		if out != src {
+			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
+		}
+	}
+}
+
+func TestBaseIndent(t *testing.T) {
+	// The testfile must not contain multi-line raw strings since those
+	// are not indented (because their values must not change) and make
+	// this test fail.
+	const filename = "printer.go"
+	src, err := ioutil.ReadFile(filename)
+	if err != nil {
+		panic(err) // error in test
+	}
+
+	file, err := parser.ParseFile(fset, filename, src, 0)
+	if err != nil {
+		panic(err) // error in test
+	}
+
+	var buf bytes.Buffer
+	for indent := 0; indent < 4; indent++ {
+		buf.Reset()
+		(&Config{Tabwidth: tabwidth, Indent: indent}).Fprint(&buf, fset, file)
+		// all code must be indented by at least 'indent' tabs
+		lines := bytes.Split(buf.Bytes(), []byte{'\n'})
+		for i, line := range lines {
+			if len(line) == 0 {
+				continue // empty lines don't have indentation
+			}
+			n := 0
+			for j, b := range line {
+				if b != '\t' {
+					// end of indentation
+					n = j
+					break
+				}
+			}
+			if n < indent {
+				t.Errorf("line %d: got only %d tabs; want at least %d: %q", i, n, indent, line)
+			}
+		}
+	}
+}
+
 // TestFuncType tests that an ast.FuncType with a nil Params field
 // can be printed (per go/ast specification). Test case for issue 3870.
 func TestFuncType(t *testing.T) {