src

purge.go (3030B)

---

 // 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"
 )
 
 // PurgeFuncBodies returns a copy of src in which the contents of each
 // outermost {...} region have been deleted, except for struct and
 // interface type bodies and the bodies of length-elided array
 // literals ([...]T), whose element count is part of the type. It
 // includes function bodies, function-literal bodies, and the bodies
 // of slice, map, and explicitly-sized array composite literals (whose
 // contents don't affect the type of the enclosing declaration). 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,
 	// and that are not the body of a length-elided array literal.
 	// That includes function bodies, switch/select bodies, and most
 	// composite literals; 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 a region we preserve
 	var ellipsis bool      // saw "[...]" not yet consumed by a literal-body "{"
 	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.SEMICOLON:
 			ellipsis = false
 
 		case token.RBRACK:
 			// "...]" occurs only in the array-type prefix of a
 			// composite literal; variadic "..." is followed by
 			// a type or ")", never "]".
 			if prev == token.ELLIPSIS {
 				ellipsis = true
 			}
 
 		case token.LBRACE:
 			if prev == token.STRUCT || prev == token.INTERFACE {
 				pos = -1 // type body: preserve (don't consume ellipsis)
 			} else if ellipsis {
 				pos = -1 // [...]T literal body: preserve
 				ellipsis = false
 			}
 			braces = append(braces, pos)
 
 		case token.RBRACE:
 			if last := len(braces) - 1; last >= 0 {
 				top := braces[last]
 				braces = braces[:last]
 				if top < 0 {
 					// preserve
 				} else if len(braces) == 0 { // toplevel only
 					// Delete {...} body.
 					start := file.Offset(top)
 					end := file.Offset(pos)
 					out.Write(src[cursor : start+len("{")])
 					cursor = end
 				}
 			}
 		}
 		prev = tok
 	}
 	out.Write(src[cursor:])
 	return out.Bytes()
 }