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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package printer
import (
"go/build/constraint"
"sort"
"text/tabwriter"
)
func (p *printer) fixGoBuildLines() {
if len(p.goBuild)+len(p.plusBuild) == 0 {
return
}
// Find latest possible placement of //go:build and // +build comments.
// That's just after the last blank line before we find a non-comment.
// (We'll add another blank line after our comment block.)
// When we start dropping // +build comments, we can skip over /* */ comments too.
// Note that we are processing tabwriter input, so every comment
// begins and ends with a tabwriter.Escape byte.
// And some newlines have turned into \f bytes.
insert := 0
for pos := 0; ; {
// Skip leading space at beginning of line.
blank := true
for pos < len(p.output) && (p.output[pos] == ' ' || p.output[pos] == '\t') {
pos++
}
// Skip over // comment if any.
if pos+3 < len(p.output) && p.output[pos] == tabwriter.Escape && p.output[pos+1] == '/' && p.output[pos+2] == '/' {
blank = false
for pos < len(p.output) && !isNL(p.output[pos]) {
pos++
}
}
// Skip over \n at end of line.
if pos >= len(p.output) || !isNL(p.output[pos]) {
break
}
pos++
if blank {
insert = pos
}
}
// If there is a //go:build comment before the place we identified,
// use that point instead. (Earlier in the file is always fine.)
if len(p.goBuild) > 0 && p.goBuild[0] < insert {
insert = p.goBuild[0]
} else if len(p.plusBuild) > 0 && p.plusBuild[0] < insert {
insert = p.plusBuild[0]
}
var x constraint.Expr
switch len(p.goBuild) {
case 0:
// Synthesize //go:build expression from // +build lines.
for _, pos := range p.plusBuild {
y, err := constraint.Parse(p.commentTextAt(pos))
if err != nil {
x = nil
break
}
if x == nil {
x = y
} else {
x = &constraint.AndExpr{X: x, Y: y}
}
}
case 1:
// Parse //go:build expression.
x, _ = constraint.Parse(p.commentTextAt(p.goBuild[0]))
}
var block []byte
if x == nil {
// Don't have a valid //go:build expression to treat as truth.
// Bring all the lines together but leave them alone.
// Note that these are already tabwriter-escaped.
for _, pos := range p.goBuild {
block = append(block, p.lineAt(pos)...)
}
for _, pos := range p.plusBuild {
block = append(block, p.lineAt(pos)...)
}
} else {
block = append(block, tabwriter.Escape)
block = append(block, "//go:build "...)
block = append(block, x.String()...)
block = append(block, tabwriter.Escape, '\n')
if len(p.plusBuild) > 0 {
lines, err := constraint.PlusBuildLines(x)
if err != nil {
lines = []string{"// +build error: " + err.Error()}
}
for _, line := range lines {
block = append(block, tabwriter.Escape)
block = append(block, line...)
block = append(block, tabwriter.Escape, '\n')
}
}
}
block = append(block, '\n')
// Build sorted list of lines to delete from remainder of output.
toDelete := append(p.goBuild, p.plusBuild...)
sort.Ints(toDelete)
// Collect output after insertion point, with lines deleted, into after.
var after []byte
start := insert
for _, end := range toDelete {
if end < start {
continue
}
after = appendLines(after, p.output[start:end])
start = end + len(p.lineAt(end))
}
after = appendLines(after, p.output[start:])
if n := len(after); n >= 2 && isNL(after[n-1]) && isNL(after[n-2]) {
after = after[:n-1]
}
p.output = p.output[:insert]
p.output = append(p.output, block...)
p.output = append(p.output, after...)
}
// appendLines is like append(x, y...)
// but it avoids creating doubled blank lines,
// which would not be gofmt-standard output.
// It assumes that only whole blocks of lines are being appended,
// not line fragments.
func appendLines(x, y []byte) []byte {
if len(y) > 0 && isNL(y[0]) && // y starts in blank line
(len(x) == 0 || len(x) >= 2 && isNL(x[len(x)-1]) && isNL(x[len(x)-2])) { // x is empty or ends in blank line
y = y[1:] // delete y's leading blank line
}
return append(x, y...)
}
func (p *printer) lineAt(start int) []byte {
pos := start
for pos < len(p.output) && !isNL(p.output[pos]) {
pos++
}
if pos < len(p.output) {
pos++
}
return p.output[start:pos]
}
func (p *printer) commentTextAt(start int) string {
if start < len(p.output) && p.output[start] == tabwriter.Escape {
start++
}
pos := start
for pos < len(p.output) && p.output[pos] != tabwriter.Escape && !isNL(p.output[pos]) {
pos++
}
return string(p.output[start:pos])
}
func isNL(b byte) bool {
return b == '\n' || b == '\f'
}
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