go/parser, go/types: accepts invalid non-if/block statements after "else" #13475
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Definitively a bug. This should not be accepted by the parser. Also, the type checker needs to double-check since the AST may have been manipulated manually and the else_ branch can contain any statement. (This is ironic given the fact that I was fighting hard to only permit |
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PS: I think I did the parser change on purpose to permit better error recovery (but then didn't add the necessary check to go/types). It's probably better to enforce syntax here since it's easy, and the syntax is very clear and unambiguous. Fix forthcoming. |
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CL https://golang.org/cl/17408 mentions this issue. |
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http://play.golang.org/p/CbXFobPaOa
This is because go/parser.(*parser).parseIfStmt simply calls go/parser.(*parser).parseStmt after consuming the ELSE token, without checking that the next token is an IF or { token. go/parser's package documentation does warn that go/parser accepts a superset of the Go grammar, so arguably this is okay for go/parser, but then I think go/types or at least go/types/gotype.go should reject it.
(Notably, cmd/gofmt inserts the necessary braces to make the code syntactically valid.)
CC @griesemer
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