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cmd/compile/internal/syntax: better error for malformed 'if' statements

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Use distinction between explicit and automatically inserted semicolons
to provide a better error message if the condition in an 'if' statement
is missing.

For #18747.

Change-Id: Iac167ae4e5ad53d2dc73f746b4dee9912434bb59
Reviewed-on: https://go-review.googlesource.com/36930
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Robert Griesemer 2017-02-13 12:48:39 -08:00
parent 02de5ed748
commit f823d30514
2 changed files with 55 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
src/cmd/compile/internal/syntax/parser.go
View File

@ -1662,7 +1662,7 @@ func (p *parser) forStmt() Stmt {
s.init(p)
p.want(_For)
s.Init, s.Cond, s.Post = p.header(true)
s.Init, s.Cond, s.Post = p.header(_For)
if gcCompat {
s.init(p)
}
@ -1688,10 +1688,13 @@ func (p *parser) stmtBody(context string) []Stmt {
return body
}
var dummyCond = &Name{Value: "false"}
func (p *parser) header(keyword token) (init SimpleStmt, cond Expr, post SimpleStmt) {
// TODO(gri) move caller's p.want(keyword) here, once we removed gcCompat
func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleStmt) {
if p.tok == _Lbrace {
if keyword == _If {
p.syntax_error("missing condition in if statement")
}
return
}
@ -1700,11 +1703,11 @@ func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleSt
if p.tok != _Semi {
// accept potential varDecl but complain
if forStmt && p.got(_Var) {
if keyword == _For && p.got(_Var) {
p.syntax_error("var declaration not allowed in for initializer")
}
init = p.simpleStmt(nil, forStmt)
// If we have a range clause, we are done.
init = p.simpleStmt(nil, keyword == _For)
// If we have a range clause, we are done (can only happen for keyword == _For).
if _, ok := init.(*RangeClause); ok {
p.xnest = outer
return
@ -1712,8 +1715,15 @@ func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleSt
}
var condStmt SimpleStmt
if p.got(_Semi) {
if forStmt {
var semi struct {
pos src.Pos
lit string
}
if p.tok == _Semi {
semi.pos = p.pos()
semi.lit = p.lit
p.next()
if keyword == _For {
if p.tok != _Semi {
condStmt = p.simpleStmt(nil, false)
}
@ -1732,12 +1742,17 @@ func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleSt
// unpack condStmt
switch s := condStmt.(type) {
case nil:
// nothing to do
if keyword == _If {
if semi.lit != "semicolon" {
p.syntax_error_at(semi.pos, fmt.Sprintf("unexpected %s, expecting { after if clause", semi.lit))
} else {
p.syntax_error_at(semi.pos, "missing condition in if statement")
}
}
case *ExprStmt:
cond = s.X
default:
p.syntax_error(fmt.Sprintf("%s used as value", String(s)))
cond = dummyCond // avoid follow-up error for if statements
}
p.xnest = outer
@ -1753,10 +1768,7 @@ func (p *parser) ifStmt() *IfStmt {
s.init(p)
p.want(_If)
s.Init, s.Cond, _ = p.header(false)
if s.Cond == nil {
p.syntax_error("missing condition in if statement")
}
s.Init, s.Cond, _ = p.header(_If)
if gcCompat {
s.init(p)
@ -1788,7 +1800,7 @@ func (p *parser) switchStmt() *SwitchStmt {
s := new(SwitchStmt)
s.init(p)
s.Init, s.Tag, _ = p.header(false)
s.Init, s.Tag, _ = p.header(_Switch)
if !p.got(_Lbrace) {
p.syntax_error("missing { after switch clause")

28
test/fixedbugs/issue18747.go Normal file
View File

@ -0,0 +1,28 @@
// errorcheck
// Copyright 2017 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 p
func _ () {
if {} // ERROR "missing condition in if statement"
if
{} // ERROR "missing condition in if statement"
if ; {} // ERROR "missing condition in if statement"
if foo; {} // ERROR "missing condition in if statement"
if foo; // ERROR "missing condition in if statement"
{}
if foo {}
if ; foo {}
if foo // ERROR "unexpected newline, expecting { after if clause"
{}
}