96 lines
2.0 KiB
Go
96 lines
2.0 KiB
Go
package parse
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import (
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"fmt"
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"io"
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"strings"
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"unicode"
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)
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// Position returns the line and column number for a certain position in a file. It is useful for recovering the position in a file that caused an error.
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// It only treates \n, \r, and \r\n as newlines, which might be different from some languages also recognizing \f, \u2028, and \u2029 to be newlines.
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func Position(r io.Reader, offset int) (line, col int, context string) {
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l := NewInput(r)
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line = 1
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for l.Pos() < offset {
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c := l.Peek(0)
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n := 1
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newline := false
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if c == '\n' {
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newline = true
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} else if c == '\r' {
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if l.Peek(1) == '\n' {
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newline = true
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n = 2
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} else {
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newline = true
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}
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} else if c >= 0xC0 {
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var r rune
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if r, n = l.PeekRune(0); r == '\u2028' || r == '\u2029' {
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newline = true
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}
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} else if c == 0 && l.Err() != nil {
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break
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}
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if 1 < n && offset < l.Pos()+n {
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break
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}
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l.Move(n)
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if newline {
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line++
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offset -= l.Pos()
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l.Skip()
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}
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}
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col = len([]rune(string(l.Lexeme()))) + 1
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context = positionContext(l, line, col)
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return
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}
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func positionContext(l *Input, line, col int) (context string) {
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for {
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c := l.Peek(0)
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if c == 0 && l.Err() != nil || c == '\n' || c == '\r' {
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break
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}
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l.Move(1)
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}
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rs := []rune(string(l.Lexeme()))
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// cut off front or rear of context to stay between 60 characters
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limit := 60
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offset := 20
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ellipsisFront := ""
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ellipsisRear := ""
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if limit < len(rs) {
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if col <= limit-offset {
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ellipsisRear = "..."
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rs = rs[:limit-3]
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} else if col >= len(rs)-offset-3 {
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ellipsisFront = "..."
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col -= len(rs) - offset - offset - 7
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rs = rs[len(rs)-offset-offset-4:]
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} else {
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ellipsisFront = "..."
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ellipsisRear = "..."
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rs = rs[col-offset-1 : col+offset]
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col = offset + 4
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}
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}
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// replace unprintable characters by a space
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for i, r := range rs {
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if !unicode.IsGraphic(r) {
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rs[i] = '·'
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}
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}
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context += fmt.Sprintf("%5d: %s%s%s\n", line, ellipsisFront, string(rs), ellipsisRear)
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context += fmt.Sprintf("%s^", strings.Repeat(" ", 6+col))
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return
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}
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