syntax.go

     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  
     5  package syntax
     6  
     7  import (
     8  	"fmt"
     9  	"io"
    10  	"os"
    11  )
    12  
    13  // Mode describes the parser mode.
    14  type Mode uint
    15  
    16  // Modes supported by the parser.
    17  const (
    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.
    22  type Error struct {
    23  	Pos Pos
    24  	Msg string
    25  }
    26  
    27  func (err Error) Error() string {
    28  	return fmt.Sprintf("%s: %s", err.Pos, err.Msg)
    29  }
    30  
    31  var _ error = Error{} // verify that Error implements error
    32  
    33  // An ErrorHandler is called for each error encountered reading a .go file.
    34  type 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.”
    39  type 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.
    53  type 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.
    66  func 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.
    84  func 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
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