src/cmd/cgo/godefs.go

// Copyright 2011 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 main

import (
	"bytes"
	"fmt"
	"go/ast"
	"go/printer"
	"go/token"
	"os"
	"path/filepath"
	"strings"
)

// godefs returns the output for -godefs mode.
func (p *Package) godefs(f *File, args []string) string {
	var buf bytes.Buffer

	fmt.Fprintf(&buf, "// Code generated by cmd/cgo -godefs; DO NOT EDIT.\n")
	fmt.Fprintf(&buf, "// %s %s\n", filepath.Base(args[0]), strings.Join(args[1:], " "))
	fmt.Fprintf(&buf, "\n")

	override := make(map[string]string)

	// Allow source file to specify override mappings.
	// For example, the socket data structures refer
	// to in_addr and in_addr6 structs but we want to be
	// able to treat them as byte arrays, so the godefs
	// inputs in package syscall say
	//
	//	// +godefs map struct_in_addr [4]byte
	//	// +godefs map struct_in_addr6 [16]byte
	//
	for _, g := range f.Comments {
		for _, c := range g.List {
			i := strings.Index(c.Text, "+godefs map")
			if i < 0 {
				continue
			}
			s := strings.TrimSpace(c.Text[i+len("+godefs map"):])
			i = strings.Index(s, " ")
			if i < 0 {
				fmt.Fprintf(os.Stderr, "invalid +godefs map comment: %s\n", c.Text)
				continue
			}
			override["_Ctype_"+strings.TrimSpace(s[:i])] = strings.TrimSpace(s[i:])
		}
	}
	for _, n := range f.Name {
		if s := override[n.Go]; s != "" {
			override[n.Mangle] = s
		}
	}

	// Otherwise, if the source file says type T C.whatever,
	// use "T" as the mangling of C.whatever,
	// except in the definition (handled at end of function).
	refName := make(map[*ast.Expr]*Name)
	for _, r := range f.Ref {
		refName[r.Expr] = r.Name
	}
	for _, d := range f.AST.Decls {
		d, ok := d.(*ast.GenDecl)
		if !ok || d.Tok != token.TYPE {
			continue
		}
		for _, s := range d.Specs {
			s := s.(*ast.TypeSpec)
			n := refName[&s.Type]
			if n != nil && n.Mangle != "" {
				override[n.Mangle] = s.Name.Name
			}
		}
	}

	// Extend overrides using typedefs:
	// If we know that C.xxx should format as T
	// and xxx is a typedef for yyy, make C.yyy format as T.
	for typ, def := range typedef {
		if new := override[typ]; new != "" {
			if id, ok := def.Go.(*ast.Ident); ok {
				override[id.Name] = new
			}
		}
	}

	// Apply overrides.
	for old, new := range override {
		if id := goIdent[old]; id != nil {
			id.Name = new
		}
	}

	// Any names still using the _C syntax are not going to compile,
	// although in general we don't know whether they all made it
	// into the file, so we can't warn here.
	//
	// The most common case is union types, which begin with
	// _Ctype_union and for which typedef[name] is a Go byte
	// array of the appropriate size (such as [4]byte).
	// Substitute those union types with byte arrays.
	for name, id := range goIdent {
		if id.Name == name && strings.Contains(name, "_Ctype_union") {
			if def := typedef[name]; def != nil {
				id.Name = gofmt(def)
			}
		}
	}

	conf.Fprint(&buf, fset, f.AST)

	return buf.String()
}

var gofmtBuf bytes.Buffer

// gofmt returns the gofmt-formatted string for an AST node.
func gofmt(n interface{}) string {
	gofmtBuf.Reset()
	err := printer.Fprint(&gofmtBuf, fset, n)
	if err != nil {
		return "<" + err.Error() + ">"
	}
	return gofmtBuf.String()
}

// gofmtLineReplacer is used to put a gofmt-formatted string for an
// AST expression onto a single line. The lexer normally inserts a
// semicolon at each newline, so we can replace newline with semicolon.
// However, we can't do that in cases where the lexer would not insert
// a semicolon. We only have to worry about cases that can occur in an
// expression passed through gofmt, which means composite literals and
// (due to the printer possibly inserting newlines because of position
// information) operators.
var gofmtLineReplacer = strings.NewReplacer(
	// Want to replace \n without ; after everything from
	// https://golang.org/ref/spec#Operators_and_punctuation
	// EXCEPT ++ -- ) ] }
	"++\n", "++;",
	"--\n", "--;",

	"+\n", "+ ",
	"-\n", "- ",
	"*\n", "* ",
	"/\n", "/ ",
	"%\n", "% ",
	"&\n", "& ",
	"|\n", "| ",
	"^\n", "^ ",
	"<\n", "< ",
	">\n", "> ",
	"=\n", "= ",
	"!\n", "! ", // not possible in gofmt today
	"(\n", "(",
	"[\n", "[", // not possible in gofmt today
	"{\n", "{",
	",\n", ",",
	".\n", ". ",
	":\n", ": ", // not possible in gofmt today

	"\n", ";",
)

// gofmtLine returns the gofmt-formatted string for an AST node,
// ensuring that it is on a single line.
func gofmtLine(n interface{}) string {
	return gofmtLineReplacer.Replace(gofmt(n))
}