[cfe-dev] [PATCH] C++ decl/expr ambiguity resolution
akyrtzi at gmail.com
Fri Aug 22 20:16:21 PDT 2008
The attached patch disambiguates between declaration or expression
statements. It uses tentative parsing and backtracking.
For the common cases no tentative parsing is needed; for the ambiguous
ones, this will result in multiple type checks (for tentative parsing
and for actual parsing).
As I've mentioned in a previous post, this can be made efficient in a
later patch by caching the type checking results of the Action module.
About the "ambiguity resoluter":
The C++ standard doesn't define in details how the ambiguity resolution
should work, it will only guarantee that if the statement is a valid
declaration, it will be parsed as a declaration.
But exactly which parts of the statement should we examine to determine
the validity of a declaration.. this is left undefined.
In practice this means that for a statement that GCC finds as invalid
declaration, Clang may parse it as valid expression.
Such differences are not important because they are about errors, the
more important "correct GCC code should be parsed correctly by
Clang"-assertion is not 'compromised'.
-If GCC parses a statement without errors, Clang will parse it the same way.
-If GCC parses a statement and emits errors because it treats it as
erroneous declaration, Clang may treat it as a correct expression instead.
Here's an example:
FuncType(a)(x,y)->z = 0;
GCC will disambiguate it as a declaration and emit errors, Clang will
disambiguate it as an expression instead.
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