syntax.go

Documentation: cmd/compile/internal/syntax

     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  	AllowGenerics
    20  )
    21  
    22  // Error describes a syntax error. Error implements the error interface.
    23  type Error struct {
    24  	Pos Pos
    25  	Msg string
    26  }
    27  
    28  func (err Error) Error() string {
    29  	return fmt.Sprintf("%s: %s", err.Pos, err.Msg)
    30  }
    31  
    32  var _ error = Error{} // verify that Error implements error
    33  
    34  // An ErrorHandler is called for each error encountered reading a .go file.
    35  type ErrorHandler func(err error)
    36  
    37  // A Pragma value augments a package, import, const, func, type, or var declaration.
    38  // Its meaning is entirely up to the PragmaHandler,
    39  // except that nil is used to mean “no pragma seen.”
    40  type Pragma interface{}
    41  
    42  // A PragmaHandler is used to process //go: directives while scanning.
    43  // It is passed the current pragma value, which starts out being nil,
    44  // and it returns an updated pragma value.
    45  // The text is the directive, with the "//" prefix stripped.
    46  // The current pragma is saved at each package, import, const, func, type, or var
    47  // declaration, into the File, ImportDecl, ConstDecl, FuncDecl, TypeDecl, or VarDecl node.
    48  //
    49  // If text is the empty string, the pragma is being returned
    50  // to the handler unused, meaning it appeared before a non-declaration.
    51  // The handler may wish to report an error. In this case, pos is the
    52  // current parser position, not the position of the pragma itself.
    53  // Blank specifies whether the line is blank before the pragma.
    54  type PragmaHandler func(pos Pos, blank bool, text string, current Pragma) Pragma
    55  
    56  // Parse parses a single Go source file from src and returns the corresponding
    57  // syntax tree. If there are errors, Parse will return the first error found,
    58  // and a possibly partially constructed syntax tree, or nil.
    59  //
    60  // If errh != nil, it is called with each error encountered, and Parse will
    61  // process as much source as possible. In this case, the returned syntax tree
    62  // is only nil if no correct package clause was found.
    63  // If errh is nil, Parse will terminate immediately upon encountering the first
    64  // error, and the returned syntax tree is nil.
    65  //
    66  // If pragh != nil, it is called with each pragma encountered.
    67  //
    68  func Parse(base *PosBase, src io.Reader, errh ErrorHandler, pragh PragmaHandler, mode Mode) (_ *File, first error) {
    69  	defer func() {
    70  		if p := recover(); p != nil {
    71  			if err, ok := p.(Error); ok {
    72  				first = err
    73  				return
    74  			}
    75  			panic(p)
    76  		}
    77  	}()
    78  
    79  	var p parser
    80  	p.init(base, src, errh, pragh, mode)
    81  	p.next()
    82  	return p.fileOrNil(), p.first
    83  }
    84  
    85  // ParseFile behaves like Parse but it reads the source from the named file.
    86  func ParseFile(filename string, errh ErrorHandler, pragh PragmaHandler, mode Mode) (*File, error) {
    87  	f, err := os.Open(filename)
    88  	if err != nil {
    89  		if errh != nil {
    90  			errh(err)
    91  		}
    92  		return nil, err
    93  	}
    94  	defer f.Close()
    95  	return Parse(NewFileBase(filename), f, errh, pragh, mode)
    96  }
    97
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