go/usr/gri/pretty/printer.go

// Copyright 2009 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 Printer

import Strings "strings"
import Scanner "scanner"
import AST "ast"
import Flag "flag"
import Fmt "fmt"
import IO "io"
import OS "os"
import TabWriter "tabwriter"

var (
	usetabs = Flag.Bool("usetabs", false, nil, "align with tabs instead of blanks");
	tabwidth = Flag.Int("tabwidth", 4, nil, "tab width");
	comments = Flag.Bool("comments", false, nil, "enable printing of comments");
)


// ----------------------------------------------------------------------------
// Support

func assert(p bool) {
	if !p {
		panic("assert failed");
	}
}


// ----------------------------------------------------------------------------
// Printer

export type Printer struct {
	writer IO.Write;
	
	// formatting control
	lastpos int;  // pos after last string
	level int;  // true scope level
	indent int;  // indentation level
	semi bool;  // pending ";"
	newl int;  // pending "\n"'s

	// comments
	clist *AST.List;
	cindex int;
	cpos int;
}


func (P *Printer) Printf(fmt string, s ...) {
	Fmt.fprintf(P.writer, fmt, s);
}


func (P *Printer) String(pos int, s string) {
	if pos == 0 {
		pos = P.lastpos;  // estimate
	}

	if P.semi && P.level > 0 {  // no semicolons at level 0
		P.Printf(";");
	}

	//print("--", pos, "[", s, "]\n");
	
	at_line_begin := false;
	for comments.BVal() && P.cpos < pos {
		//print("cc", P.cpos, "\n");
		
		// we have a comment that comes before s
		comment := P.clist.at(P.cindex).(*AST.Comment);
		text := comment.text;
		assert(len(text) >= 3);  // classification char + "//" or "/*"
		
		// classify comment
		switch comment.tok {
		case Scanner.COMMENT_BB:
			// black space before and after comment on the same line
			// - print surrounded by blanks
			P.Printf(" %s ", text);

		case Scanner.COMMENT_BW:
			// only white space after comment on the same line
			// - put into next cell
			P.Printf("\t%s", text);
			
		case Scanner.COMMENT_WW, Scanner.COMMENT_WB:
			// only white space before comment on the same line
			// - indent
			/*
			if !P.buf.EmptyLine() {
				P.buf.Newline();
			}
			*/
			for i := P.indent; i > 0; i-- {
				P.Printf("\t");
			}
			P.Printf("%s", text);

		default:
			panic("UNREACHABLE");
		}
		
		if text[1] == '/' {
			// line comments must end in newline
			// TODO should we set P.newl instead?
			P.Printf("\n");
			for i := P.indent; i > 0; i-- {
				P.Printf("\t");
			}
			at_line_begin = true;
		}

		P.cindex++;
		if P.cindex < P.clist.len() {
			P.cpos = P.clist.at(P.cindex).(*AST.Comment).pos;
		} else {
			P.cpos = 1000000000;  // infinite
		}
	}

	if at_line_begin && P.newl > 0 {
		P.newl--;
	}
	
	if P.newl > 0 {
		P.Printf("\n");
		if P.newl > 1 {
			for i := P.newl; i > 1; i-- {
				P.Printf("\n");
			}
		}
		for i := P.indent; i > 0; i-- {
			P.Printf("\t");
		}
	}

	P.Printf("%s", s);

	P.lastpos = pos + len(s);
	P.semi, P.newl = false, 0;
}


func (P *Printer) Blank() {
	P.String(0, " ");
}


func (P *Printer) Tab() {
	P.String(0, "\t");
}


func (P *Printer) Token(pos int, tok int) {
	P.String(pos, Scanner.TokenString(tok));
}


func (P *Printer) OpenScope(paren string) {
	//P.semi, P.newl = false, 0;
	P.String(0, paren);
	P.level++;
	P.indent++;
	P.newl = 1;
}


func (P *Printer) CloseScope(paren string) {
	P.indent--;
	P.semi = false;
	P.String(0, paren);
	P.level--;
	P.semi, P.newl = false, 1;
}


func (P *Printer) Error(pos int, tok int, msg string) {
	P.String(0, "<");
	P.Token(pos, tok);
	P.String(0, " " + msg + ">");
}


// ----------------------------------------------------------------------------
// Types

func (P *Printer) Type(t *AST.Type)
func (P *Printer) Expr(x *AST.Expr)

func (P *Printer) Parameters(pos int, list *AST.List) {
	P.String(pos, "(");
	var prev int;
	for i, n := 0, list.len(); i < n; i++ {
		x := list.at(i).(*AST.Expr);
		if i > 0 {
			if prev == x.tok || prev == Scanner.TYPE {
				P.String(0, ", ");
			} else {
				P.Blank();
			}
		}
		P.Expr(x);
		prev = x.tok;
	}
	P.String(0, ")");
}


func (P *Printer) Fields(list *AST.List) {
	P.OpenScope("{");
	var prev int;
	for i, n := 0, list.len(); i < n; i++ {
		x := list.at(i).(*AST.Expr);
		if i > 0 {
			if prev == Scanner.TYPE && x.tok != Scanner.STRING || prev == Scanner.STRING {
				P.semi, P.newl = true, 1;
			} else if prev == x.tok {
				P.String(0, ", ");
			} else {
				P.Tab();
			}
		}
		P.Expr(x);
		prev = x.tok;
	}
	P.newl = 1;
	P.CloseScope("}");
}


func (P *Printer) Type(t *AST.Type) {
	switch t.tok {
	case Scanner.IDENT:
		P.Expr(t.expr);

	case Scanner.LBRACK:
		P.String(t.pos, "[");
		if t.expr != nil {
			P.Expr(t.expr);
		}
		P.String(0, "]");
		P.Type(t.elt);

	case Scanner.STRUCT, Scanner.INTERFACE:
		P.Token(t.pos, t.tok);
		if t.list != nil {
			P.Blank();
			P.Fields(t.list);
		}

	case Scanner.MAP:
		P.String(t.pos, "map [");
		P.Type(t.key);
		P.String(0, "]");
		P.Type(t.elt);

	case Scanner.CHAN:
		var m string;
		switch t.mode {
		case AST.FULL: m = "chan ";
		case AST.RECV: m = "<-chan ";
		case AST.SEND: m = "chan <- ";
		}
		P.String(t.pos, m);
		P.Type(t.elt);

	case Scanner.MUL:
		P.String(t.pos, "*");
		P.Type(t.elt);

	case Scanner.LPAREN:
		P.Parameters(t.pos, t.list);
		if t.elt != nil {
			P.Blank();
			P.Parameters(0, t.elt.list);
		}

	case Scanner.ELLIPSIS:
		P.String(t.pos, "...");

	default:
		P.Error(t.pos, t.tok, "type");
	}
}


// ----------------------------------------------------------------------------
// Expressions

func (P *Printer) Block(list *AST.List, indent bool);

func (P *Printer) Expr1(x *AST.Expr, prec1 int) {
	if x == nil {
		return;  // empty expression list
	}

	switch x.tok {
	case Scanner.TYPE:
		// type expr
		P.Type(x.t);

	case Scanner.IDENT, Scanner.INT, Scanner.STRING, Scanner.FLOAT:
		// literal
		P.String(x.pos, x.s);

	case Scanner.FUNC:
		// function literal
		P.String(x.pos, "func");
		P.Type(x.t);
		P.Block(x.block, true);
		P.newl = 0;

	case Scanner.COMMA:
		// list
		// (don't use binary expression printing because of different spacing)
		P.Expr(x.x);
		P.String(x.pos, ", ");
		P.Expr(x.y);

	case Scanner.PERIOD:
		// selector or type guard
		P.Expr1(x.x, Scanner.HighestPrec);
		P.String(x.pos, ".");
		if x.y != nil {
			P.Expr1(x.y, Scanner.HighestPrec);
		} else {
			P.String(0, "(");
			P.Type(x.t);
			P.String(0, ")");
		}
		
	case Scanner.LBRACK:
		// index
		P.Expr1(x.x, Scanner.HighestPrec);
		P.String(x.pos, "[");
		P.Expr1(x.y, 0);
		P.String(0, "]");

	case Scanner.LPAREN:
		// call
		P.Expr1(x.x, Scanner.HighestPrec);
		P.String(x.pos, "(");
		P.Expr(x.y);
		P.String(0, ")");

	case Scanner.LBRACE:
		// composite
		P.Type(x.t);
		P.String(x.pos, "{");
		P.Expr(x.y);
		P.String(0, "}");
		
	default:
		// unary and binary expressions including ":" for pairs
		prec := Scanner.UnaryPrec;
		if x.x != nil {
			prec = Scanner.Precedence(x.tok);
		}
		if prec < prec1 {
			P.String(0, "(");
		}
		if x.x == nil {
			// unary expression
			P.Token(x.pos, x.tok);
		} else {
			// binary expression
			P.Expr1(x.x, prec);
			P.Blank();
			P.Token(x.pos, x.tok);
			P.Blank();
		}
		P.Expr1(x.y, prec);
		if prec < prec1 {
			P.String(0, ")");
		}
	}
}


func (P *Printer) Expr(x *AST.Expr) {
	P.Expr1(x, Scanner.LowestPrec);
}


// ----------------------------------------------------------------------------
// Statements

func (P *Printer) Stat(s *AST.Stat)

func (P *Printer) StatementList(list *AST.List) {
	for i, n := 0, list.len(); i < n; i++ {
		P.Stat(list.at(i).(*AST.Stat));
		P.newl = 1;
	}
}


func (P *Printer) Block(list *AST.List, indent bool) {
	P.OpenScope("{");
	if !indent {
		P.indent--;
	}
	P.StatementList(list);
	if !indent {
		P.indent++;
	}
	P.CloseScope("}");
}


func (P *Printer) ControlClause(s *AST.Stat) {
	has_post := s.tok == Scanner.FOR && s.post != nil;  // post also used by "if"
	if s.init == nil && !has_post {
		// no semicolons required
		if s.expr != nil {
			P.Blank();
			P.Expr(s.expr);
		}
	} else {
		// all semicolons required
		P.Blank();
		if s.init != nil {
			P.Stat(s.init);
		}
		P.semi = true;
		P.Blank();
		if s.expr != nil {
			P.Expr(s.expr);
		}
		if s.tok == Scanner.FOR {
			P.semi = true;
			if has_post {
				P.Blank();
				P.Stat(s.post);
				P.semi = false
			}
		}
	}
	P.Blank();
}


func (P *Printer) Declaration(d *AST.Decl, parenthesized bool);

func (P *Printer) Stat(s *AST.Stat) {
	switch s.tok {
	case Scanner.EXPRSTAT:
		// expression statement
		P.Expr(s.expr);
		P.semi = true;

	case Scanner.COLON:
		// label declaration
		P.indent--;
		P.Expr(s.expr);
		P.Token(s.pos, s.tok);
		P.indent++;
		P.semi = false;
		
	case Scanner.CONST, Scanner.TYPE, Scanner.VAR:
		// declaration
		P.Declaration(s.decl, false);

	case Scanner.INC, Scanner.DEC:
		P.Expr(s.expr);
		P.Token(s.pos, s.tok);
		P.semi = true;

	case Scanner.LBRACE:
		// block
		P.Block(s.block, true);

	case Scanner.IF:
		P.String(s.pos, "if");
		P.ControlClause(s);
		P.Block(s.block, true);
		if s.post != nil {
			P.newl = 0;
			P.String(0, " else ");
			P.Stat(s.post);
		}

	case Scanner.FOR:
		P.String(s.pos, "for");
		P.ControlClause(s);
		P.Block(s.block, true);

	case Scanner.SWITCH, Scanner.SELECT:
		P.Token(s.pos, s.tok);
		P.ControlClause(s);
		P.Block(s.block, false);

	case Scanner.CASE, Scanner.DEFAULT:
		P.Token(s.pos, s.tok);
		if s.expr != nil {
			P.Blank();
			P.Expr(s.expr);
		}
		P.String(0, ":");
		P.indent++;
		P.newl = 1;
		P.StatementList(s.block);
		P.indent--;
		P.newl = 1;

	case Scanner.GO, Scanner.RETURN, Scanner.FALLTHROUGH, Scanner.BREAK, Scanner.CONTINUE, Scanner.GOTO:
		P.Token(s.pos, s.tok);
		if s.expr != nil {
			P.Blank();
			P.Expr(s.expr);
		}
		P.semi = true;

	default:
		P.Error(s.pos, s.tok, "stat");
	}
}


// ----------------------------------------------------------------------------
// Declarations


func (P *Printer) Declaration(d *AST.Decl, parenthesized bool) {
	if !parenthesized {
		if d.exported {
			P.String(d.pos, "export ");
		}
		P.Token(d.pos, d.tok);
		P.Blank();
	}

	if d.tok != Scanner.FUNC && d.list != nil {
		P.OpenScope("(");
		for i := 0; i < d.list.len(); i++ {
			P.Declaration(d.list.at(i).(*AST.Decl), true);
			P.semi, P.newl = true, 1;
		}
		P.CloseScope(")");

	} else {
		if d.tok == Scanner.FUNC && d.typ.key != nil {
			P.Parameters(0, d.typ.key.list);
			P.Blank();
		}

		P.Expr(d.ident);
		
		if d.typ != nil {
			if d.tok != Scanner.FUNC {
				P.Blank();
			}
			P.Type(d.typ);
		}

		if d.val != nil {
			P.Tab();
			if d.tok != Scanner.IMPORT {
				P.String(0, "= ");
			}
			P.Expr(d.val);
		}

		if d.list != nil {
			if d.tok != Scanner.FUNC {
				panic("must be a func declaration");
			}
			P.Blank();
			P.Block(d.list, true);
		}
		
		if d.tok != Scanner.TYPE {
			P.semi = true;
		}
	}
	
	P.newl = 1;

	// extra newline after a function declaration
	if d.tok == Scanner.FUNC {
		P.newl++;
	}
	
	// extra newline at the top level
	if P.level == 0 {
		P.newl++;
	}
}


// ----------------------------------------------------------------------------
// Program

func (P *Printer) Program(p *AST.Program) {
	// TODO should initialize all fields?
	P.writer = TabWriter.MakeTabWriter(OS.Stdout, usetabs.BVal(), int(tabwidth.IVal()));
	
	P.clist = p.comments;
	P.cindex = 0;
	if p.comments.len() > 0 {
		P.cpos = p.comments.at(0).(*AST.Comment).pos;
	} else {
		P.cpos = 1000000000;  // infinite
	}

	// Print package
	P.String(p.pos, "package ");
	P.Expr(p.ident);
	P.newl = 2;
	for i := 0; i < p.decls.len(); i++ {
		P.Declaration(p.decls.at(i), false);
	}
	P.newl = 2;	// TODO we should be able to do this with 1 instead of 2
				// but we are loosing the last buffer flush in that case

	P.String(0, "");  // flush buffer
}