2 files changed, 323 insertions, 0 deletions
diff --git a/src/go/format/format.go b/src/go/format/format.go
new file mode 100644
index 000000000..3d00a645d
--- /dev/null
+++ b/src/go/format/format.go
@@ -0,0 +1,199 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package format implements standard formatting of Go source.
+package format
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"io"
+	"strings"
+)
+
+var config = printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
+
+// Node formats node in canonical gofmt style and writes the result to dst.
+//
+// The node type must be *ast.File, *printer.CommentedNode, []ast.Decl,
+// []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec,
+// or ast.Stmt. Node does not modify node. Imports are not sorted for
+// nodes representing partial source files (i.e., if the node is not an
+// *ast.File or a *printer.CommentedNode not wrapping an *ast.File).
+//
+// The function may return early (before the entire result is written)
+// and return a formatting error, for instance due to an incorrect AST.
+//
+func Node(dst io.Writer, fset *token.FileSet, node interface{}) error {
+	// Determine if we have a complete source file (file != nil).
+	var file *ast.File
+	var cnode *printer.CommentedNode
+	switch n := node.(type) {
+	case *ast.File:
+		file = n
+	case *printer.CommentedNode:
+		if f, ok := n.Node.(*ast.File); ok {
+			file = f
+			cnode = n
+		}
+	}
+
+	// Sort imports if necessary.
+	if file != nil && hasUnsortedImports(file) {
+		// Make a copy of the AST because ast.SortImports is destructive.
+		// TODO(gri) Do this more efficiently.
+		var buf bytes.Buffer
+		err := config.Fprint(&buf, fset, file)
+		if err != nil {
+			return err
+		}
+		file, err = parser.ParseFile(fset, "", buf.Bytes(), parser.ParseComments)
+		if err != nil {
+			// We should never get here. If we do, provide good diagnostic.
+			return fmt.Errorf("format.Node internal error (%s)", err)
+		}
+		ast.SortImports(fset, file)
+
+		// Use new file with sorted imports.
+		node = file
+		if cnode != nil {
+			node = &printer.CommentedNode{Node: file, Comments: cnode.Comments}
+		}
+	}
+
+	return config.Fprint(dst, fset, node)
+}
+
+// Source formats src in canonical gofmt style and returns the result
+// or an (I/O or syntax) error. src is expected to be a syntactically
+// correct Go source file, or a list of Go declarations or statements.
+//
+// If src is a partial source file, the leading and trailing space of src
+// is applied to the result (such that it has the same leading and trailing
+// space as src), and the result is indented by the same amount as the first
+// line of src containing code. Imports are not sorted for partial source files.
+//
+func Source(src []byte) ([]byte, error) {
+	fset := token.NewFileSet()
+	node, err := parse(fset, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var buf bytes.Buffer
+	if file, ok := node.(*ast.File); ok {
+		// Complete source file.
+		ast.SortImports(fset, file)
+		err := config.Fprint(&buf, fset, file)
+		if err != nil {
+			return nil, err
+		}
+
+	} else {
+		// Partial source file.
+		// Determine and prepend leading space.
+		i, j := 0, 0
+		for j < len(src) && isSpace(src[j]) {
+			if src[j] == '\n' {
+				i = j + 1 // index of last line in leading space
+			}
+			j++
+		}
+		buf.Write(src[:i])
+
+		// Determine indentation of first code line.
+		// Spaces are ignored unless there are no tabs,
+		// in which case spaces count as one tab.
+		indent := 0
+		hasSpace := false
+		for _, b := range src[i:j] {
+			switch b {
+			case ' ':
+				hasSpace = true
+			case '\t':
+				indent++
+			}
+		}
+		if indent == 0 && hasSpace {
+			indent = 1
+		}
+
+		// Format the source.
+		cfg := config
+		cfg.Indent = indent
+		err := cfg.Fprint(&buf, fset, node)
+		if err != nil {
+			return nil, err
+		}
+
+		// Determine and append trailing space.
+		i = len(src)
+		for i > 0 && isSpace(src[i-1]) {
+			i--
+		}
+		buf.Write(src[i:])
+	}
+
+	return buf.Bytes(), nil
+}
+
+func hasUnsortedImports(file *ast.File) bool {
+	for _, d := range file.Decls {
+		d, ok := d.(*ast.GenDecl)
+		if !ok || d.Tok != token.IMPORT {
+			// Not an import declaration, so we're done.
+			// Imports are always first.
+			return false
+		}
+		if d.Lparen.IsValid() {
+			// For now assume all grouped imports are unsorted.
+			// TODO(gri) Should check if they are sorted already.
+			return true
+		}
+		// Ungrouped imports are sorted by default.
+	}
+	return false
+}
+
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}
+
+func parse(fset *token.FileSet, src []byte) (interface{}, error) {
+	// Try as a complete source file.
+	file, err := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err == nil {
+		return file, nil
+	}
+	// If the source is missing a package clause, try as a source fragment; otherwise fail.
+	if !strings.Contains(err.Error(), "expected 'package'") {
+		return nil, err
+	}
+
+	// Try as a declaration list by prepending a package clause in front of src.
+	// Use ';' not '\n' to keep line numbers intact.
+	psrc := append([]byte("package p;"), src...)
+	file, err = parser.ParseFile(fset, "", psrc, parser.ParseComments)
+	if err == nil {
+		return file.Decls, nil
+	}
+	// If the source is missing a declaration, try as a statement list; otherwise fail.
+	if !strings.Contains(err.Error(), "expected declaration") {
+		return nil, err
+	}
+
+	// Try as statement list by wrapping a function around src.
+	fsrc := append(append([]byte("package p; func _() {"), src...), '}')
+	file, err = parser.ParseFile(fset, "", fsrc, parser.ParseComments)
+	if err == nil {
+		return file.Decls[0].(*ast.FuncDecl).Body.List, nil
+	}
+
+	// Failed, and out of options.
+	return nil, err
+}
diff --git a/src/go/format/format_test.go b/src/go/format/format_test.go
new file mode 100644
index 000000000..93f099247
--- /dev/null
+++ b/src/go/format/format_test.go
@@ -0,0 +1,124 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package format
+
+import (
+	"bytes"
+	"go/parser"
+	"go/token"
+	"io/ioutil"
+	"strings"
+	"testing"
+)
+
+const testfile = "format_test.go"
+
+func diff(t *testing.T, dst, src []byte) {
+	line := 1
+	offs := 0 // line offset
+	for i := 0; i < len(dst) && i < len(src); i++ {
+		d := dst[i]
+		s := src[i]
+		if d != s {
+			t.Errorf("dst:%d: %s\n", line, dst[offs:i+1])
+			t.Errorf("src:%d: %s\n", line, src[offs:i+1])
+			return
+		}
+		if s == '\n' {
+			line++
+			offs = i + 1
+		}
+	}
+	if len(dst) != len(src) {
+		t.Errorf("len(dst) = %d, len(src) = %d\nsrc = %q", len(dst), len(src), src)
+	}
+}
+
+func TestNode(t *testing.T) {
+	src, err := ioutil.ReadFile(testfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, testfile, src, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+
+	if err = Node(&buf, fset, file); err != nil {
+		t.Fatal("Node failed:", err)
+	}
+
+	diff(t, buf.Bytes(), src)
+}
+
+func TestSource(t *testing.T) {
+	src, err := ioutil.ReadFile(testfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	res, err := Source(src)
+	if err != nil {
+		t.Fatal("Source failed:", err)
+	}
+
+	diff(t, res, src)
+}
+
+// Test cases that are expected to fail are marked by the prefix "ERROR".
+var tests = []string{
+	// declaration lists
+	`import "go/format"`,
+	"var x int",
+	"var x int\n\ntype T struct{}",
+
+	// statement lists
+	"x := 0",
+	"f(a, b, c)\nvar x int = f(1, 2, 3)",
+
+	// indentation, leading and trailing space
+	"\tx := 0\n\tgo f()",
+	"\tx := 0\n\tgo f()\n\n\n",
+	"\n\t\t\n\n\tx := 0\n\tgo f()\n\n\n",
+	"\n\t\t\n\n\t\t\tx := 0\n\t\t\tgo f()\n\n\n",
+	"\n\t\t\n\n\t\t\tx := 0\n\t\t\tconst s = `\nfoo\n`\n\n\n", // no indentation inside raw strings
+
+	// erroneous programs
+	"ERROR1 + 2 +",
+	"ERRORx :=  0",
+}
+
+func String(s string) (string, error) {
+	res, err := Source([]byte(s))
+	if err != nil {
+		return "", err
+	}
+	return string(res), nil
+}
+
+func TestPartial(t *testing.T) {
+	for _, src := range tests {
+		if strings.HasPrefix(src, "ERROR") {
+			// test expected to fail
+			src = src[5:] // remove ERROR prefix
+			res, err := String(src)
+			if err == nil && res == src {
+				t.Errorf("formatting succeeded but was expected to fail:\n%q", src)
+			}
+		} else {
+			// test expected to succeed
+			res, err := String(src)
+			if err != nil {
+				t.Errorf("formatting failed (%s):\n%q", err, src)
+			} else if res != src {
+				t.Errorf("formatting incorrect:\nsource: %q\nresult: %q", src, res)
+			}
+		}
+	}
+}