errors.go

Documentation: go/scanner

		 1  // Copyright 2009 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 scanner
		 6  
		 7  import (
		 8  	"fmt"
		 9  	"go/token"
		10  	"io"
		11  	"sort"
		12  )
		13  
		14  // In an ErrorList, an error is represented by an *Error.
		15  // The position Pos, if valid, points to the beginning of
		16  // the offending token, and the error condition is described
		17  // by Msg.
		18  //
		19  type Error struct {
		20  	Pos token.Position
		21  	Msg string
		22  }
		23  
		24  // Error implements the error interface.
		25  func (e Error) Error() string {
		26  	if e.Pos.Filename != "" || e.Pos.IsValid() {
		27  		// don't print "<unknown position>"
		28  		// TODO(gri) reconsider the semantics of Position.IsValid
		29  		return e.Pos.String() + ": " + e.Msg
		30  	}
		31  	return e.Msg
		32  }
		33  
		34  // ErrorList is a list of *Errors.
		35  // The zero value for an ErrorList is an empty ErrorList ready to use.
		36  //
		37  type ErrorList []*Error
		38  
		39  // Add adds an Error with given position and error message to an ErrorList.
		40  func (p *ErrorList) Add(pos token.Position, msg string) {
		41  	*p = append(*p, &Error{pos, msg})
		42  }
		43  
		44  // Reset resets an ErrorList to no errors.
		45  func (p *ErrorList) Reset() { *p = (*p)[0:0] }
		46  
		47  // ErrorList implements the sort Interface.
		48  func (p ErrorList) Len() int			{ return len(p) }
		49  func (p ErrorList) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
		50  
		51  func (p ErrorList) Less(i, j int) bool {
		52  	e := &p[i].Pos
		53  	f := &p[j].Pos
		54  	// Note that it is not sufficient to simply compare file offsets because
		55  	// the offsets do not reflect modified line information (through //line
		56  	// comments).
		57  	if e.Filename != f.Filename {
		58  		return e.Filename < f.Filename
		59  	}
		60  	if e.Line != f.Line {
		61  		return e.Line < f.Line
		62  	}
		63  	if e.Column != f.Column {
		64  		return e.Column < f.Column
		65  	}
		66  	return p[i].Msg < p[j].Msg
		67  }
		68  
		69  // Sort sorts an ErrorList. *Error entries are sorted by position,
		70  // other errors are sorted by error message, and before any *Error
		71  // entry.
		72  //
		73  func (p ErrorList) Sort() {
		74  	sort.Sort(p)
		75  }
		76  
		77  // RemoveMultiples sorts an ErrorList and removes all but the first error per line.
		78  func (p *ErrorList) RemoveMultiples() {
		79  	sort.Sort(p)
		80  	var last token.Position // initial last.Line is != any legal error line
		81  	i := 0
		82  	for _, e := range *p {
		83  		if e.Pos.Filename != last.Filename || e.Pos.Line != last.Line {
		84  			last = e.Pos
		85  			(*p)[i] = e
		86  			i++
		87  		}
		88  	}
		89  	*p = (*p)[0:i]
		90  }
		91  
		92  // An ErrorList implements the error interface.
		93  func (p ErrorList) Error() string {
		94  	switch len(p) {
		95  	case 0:
		96  		return "no errors"
		97  	case 1:
		98  		return p[0].Error()
		99  	}
	 100  	return fmt.Sprintf("%s (and %d more errors)", p[0], len(p)-1)
	 101  }
	 102  
	 103  // Err returns an error equivalent to this error list.
	 104  // If the list is empty, Err returns nil.
	 105  func (p ErrorList) Err() error {
	 106  	if len(p) == 0 {
	 107  		return nil
	 108  	}
	 109  	return p
	 110  }
	 111  
	 112  // PrintError is a utility function that prints a list of errors to w,
	 113  // one error per line, if the err parameter is an ErrorList. Otherwise
	 114  // it prints the err string.
	 115  //
	 116  func PrintError(w io.Writer, err error) {
	 117  	if list, ok := err.(ErrorList); ok {
	 118  		for _, e := range list {
	 119  			fmt.Fprintf(w, "%s\n", e)
	 120  		}
	 121  	} else if err != nil {
	 122  		fmt.Fprintf(w, "%s\n", err)
	 123  	}
	 124  }
	 125
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