[cfe-commits] [PATCH] Improved error-recovery for malformed declarations

[Richard Smith]

Hi,

Currently, after a malformed declaration, clang skips until it reaches an
unparenthesized '}' or ';'. One fairly common error (especially among vim
users) is for the first line of a file to have junk in it. This leads to
abysmal error recovery, where we skip all 'namespace { ... }' and 'extern
"C" { ... }' blocks and function definitions until we get to a top-level
semicolon (which often doesn't arrive until we're past all the #included
header files and somewhere in the main source file). We then produce a
large pile of incorrect diagnostics, because we have not seen any
declarations yet.

The attached patch improves this situation by tweaking the recovery
heuristic as follows: we skip the shortest sequence of
brace/bracket/paren-balanced tokens which either ends with a semicolon or a
close brace[1] (and any following semicolon), or is followed by a namespace
definition at the start of a line.

In my testing, this seems to be a strict improvement. Does this seem like a
reasonable change? I'm sure there are other places where this style of
recovery would be a better option than a simple SkipUntil(tok::r_brace),
but I don't have evidence of a specific common pattern of errors leading to
poor recovery elsewhere.

Thanks!
Richard

[1] If the close brace is followed by ',', '{' or 'try', we could be in the
initializer-list for a constructor, so we keep skipping.
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