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// Copyright 2023 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 astutil provides various AST utility functions for gopls.
package astutil
import (
"bytes"
"go/scanner"
"go/token"
"cuelang.org/go/internal/golangorgx/gopls/util/safetoken"
)
// PurgeFuncBodies returns a copy of src in which the contents of each
// outermost {...} region except struct and interface types have been
// deleted. This reduces the amount of work required to parse the
// top-level declarations.
//
// PurgeFuncBodies does not preserve newlines or position information.
// Also, if the input is invalid, parsing the output of
// PurgeFuncBodies may result in a different tree due to its effects
// on parser error recovery.
func PurgeFuncBodies(src []byte) []byte {
// Destroy the content of any {...}-bracketed regions that are
// not immediately preceded by a "struct" or "interface"
// token. That includes function bodies, composite literals,
// switch/select bodies, and all blocks of statements.
// This will lead to non-void functions that don't have return
// statements, which of course is a type error, but that's ok.
var out bytes.Buffer
file := token.NewFileSet().AddFile("", -1, len(src))
var sc scanner.Scanner
sc.Init(file, src, nil, 0)
var prev token.Token
var cursor int // last consumed src offset
var braces []token.Pos // stack of unclosed braces or -1 for struct/interface type
for {
pos, tok, _ := sc.Scan()
if tok == token.EOF {
break
}
switch tok {
case token.COMMENT:
// TODO(adonovan): opt: skip, to save an estimated 20% of time.
case token.LBRACE:
if prev == token.STRUCT || prev == token.INTERFACE {
pos = -1
}
braces = append(braces, pos)
case token.RBRACE:
if last := len(braces) - 1; last >= 0 {
top := braces[last]
braces = braces[:last]
if top < 0 {
// struct/interface type: leave alone
} else if len(braces) == 0 { // toplevel only
// Delete {...} body.
start, _ := safetoken.Offset(file, top)
end, _ := safetoken.Offset(file, pos)
out.Write(src[cursor : start+len("{")])
cursor = end
}
}
}
prev = tok
}
out.Write(src[cursor:])
return out.Bytes()
}
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