59 lines
1.6 KiB
Go
59 lines
1.6 KiB
Go
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/*
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Copyright 2011 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package errorutil helps make better error messages.
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package errorutil // import "go4.org/errorutil"
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"strings"
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)
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// HighlightBytePosition takes a reader and the location in bytes of a parse
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// error (for instance, from json.SyntaxError.Offset) and returns the line, column,
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// and pretty-printed context around the error with an arrow indicating the exact
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// position of the syntax error.
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func HighlightBytePosition(f io.Reader, pos int64) (line, col int, highlight string) {
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line = 1
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br := bufio.NewReader(f)
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lastLine := ""
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thisLine := new(bytes.Buffer)
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for n := int64(0); n < pos; n++ {
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b, err := br.ReadByte()
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if err != nil {
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break
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}
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if b == '\n' {
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lastLine = thisLine.String()
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thisLine.Reset()
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line++
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col = 1
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} else {
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col++
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thisLine.WriteByte(b)
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}
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}
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if line > 1 {
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highlight += fmt.Sprintf("%5d: %s\n", line-1, lastLine)
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}
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highlight += fmt.Sprintf("%5d: %s\n", line, thisLine.String())
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highlight += fmt.Sprintf("%s^\n", strings.Repeat(" ", col+5))
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return
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}
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