Source file src/pkg/go/scanner/errors.go

     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 true
    59		}
    60		if e.Filename == f.Filename {
    61			if e.Line < f.Line {
    62				return true
    63			}
    64			if e.Line == f.Line {
    65				return e.Column < f.Column
    66			}
    67		}
    68		return false
    69	}
    70	
    71	// Sort sorts an ErrorList. *Error entries are sorted by position,
    72	// other errors are sorted by error message, and before any *Error
    73	// entry.
    74	//
    75	func (p ErrorList) Sort() {
    76		sort.Sort(p)
    77	}
    78	
    79	// RemoveMultiples sorts an ErrorList and removes all but the first error per line.
    80	func (p *ErrorList) RemoveMultiples() {
    81		sort.Sort(p)
    82		var last token.Position // initial last.Line is != any legal error line
    83		i := 0
    84		for _, e := range *p {
    85			if e.Pos.Filename != last.Filename || e.Pos.Line != last.Line {
    86				last = e.Pos
    87				(*p)[i] = e
    88				i++
    89			}
    90		}
    91		(*p) = (*p)[0:i]
    92	}
    93	
    94	// An ErrorList implements the error interface.
    95	func (p ErrorList) Error() string {
    96		switch len(p) {
    97		case 0:
    98			return "no errors"
    99		case 1:
   100			return p[0].Error()
   101		}
   102		return fmt.Sprintf("%s (and %d more errors)", p[0], len(p)-1)
   103	}
   104	
   105	// Err returns an error equivalent to this error list.
   106	// If the list is empty, Err returns nil.
   107	func (p ErrorList) Err() error {
   108		if len(p) == 0 {
   109			return nil
   110		}
   111		return p
   112	}
   113	
   114	// PrintError is a utility function that prints a list of errors to w,
   115	// one error per line, if the err parameter is an ErrorList. Otherwise
   116	// it prints the err string.
   117	//
   118	func PrintError(w io.Writer, err error) {
   119		if list, ok := err.(ErrorList); ok {
   120			for _, e := range list {
   121				fmt.Fprintf(w, "%s\n", e)
   122			}
   123		} else {
   124			fmt.Fprintf(w, "%s\n", err)
   125		}
   126	}