1// Copyright 2016 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package syntax
6
7import (
8	"fmt"
9	"io"
10	"os"
11)
12
13// Mode describes the parser mode.
14type Mode uint
15
16// Modes supported by the parser.
17const (
18	CheckBranches Mode = 1 << iota // check correct use of labels, break, continue, and goto statements
19)
20
21// Error describes a syntax error. Error implements the error interface.
22type Error struct {
23	Pos Pos
24	Msg string
25}
26
27func (err Error) Error() string {
28	return fmt.Sprintf("%s: %s", err.Pos, err.Msg)
29}
30
31var _ error = Error{} // verify that Error implements error
32
33// An ErrorHandler is called for each error encountered reading a .go file.
34type ErrorHandler func(err error)
35
36// A Pragma value augments a package, import, const, func, type, or var declaration.
37// Its meaning is entirely up to the PragmaHandler,
38// except that nil is used to mean “no pragma seen.”
39type Pragma interface{}
40
41// A PragmaHandler is used to process //go: directives while scanning.
42// It is passed the current pragma value, which starts out being nil,
43// and it returns an updated pragma value.
44// The text is the directive, with the "//" prefix stripped.
45// The current pragma is saved at each package, import, const, func, type, or var
46// declaration, into the File, ImportDecl, ConstDecl, FuncDecl, TypeDecl, or VarDecl node.
47//
48// If text is the empty string, the pragma is being returned
49// to the handler unused, meaning it appeared before a non-declaration.
50// The handler may wish to report an error. In this case, pos is the
51// current parser position, not the position of the pragma itself.
52// Blank specifies whether the line is blank before the pragma.
53type PragmaHandler func(pos Pos, blank bool, text string, current Pragma) Pragma
54
55// Parse parses a single Go source file from src and returns the corresponding
56// syntax tree. If there are errors, Parse will return the first error found,
57// and a possibly partially constructed syntax tree, or nil.
58//
59// If errh != nil, it is called with each error encountered, and Parse will
60// process as much source as possible. In this case, the returned syntax tree
61// is only nil if no correct package clause was found.
62// If errh is nil, Parse will terminate immediately upon encountering the first
63// error, and the returned syntax tree is nil.
64//
65// If pragh != nil, it is called with each pragma encountered.
66func Parse(base *PosBase, src io.Reader, errh ErrorHandler, pragh PragmaHandler, mode Mode) (_ *File, first error) {
67	defer func() {
68		if p := recover(); p != nil {
69			if err, ok := p.(Error); ok {
70				first = err
71				return
72			}
73			panic(p)
74		}
75	}()
76
77	var p parser
78	p.init(base, src, errh, pragh, mode)
79	p.next()
80	return p.fileOrNil(), p.first
81}
82
83// ParseFile behaves like Parse but it reads the source from the named file.
84func ParseFile(filename string, errh ErrorHandler, pragh PragmaHandler, mode Mode) (*File, error) {
85	f, err := os.Open(filename)
86	if err != nil {
87		if errh != nil {
88			errh(err)
89		}
90		return nil, err
91	}
92	defer f.Close()
93	return Parse(NewFileBase(filename), f, errh, pragh, mode)
94}
95