• Vladislav Zavialov's avatar
    Parser API annotations: RealSrcLoc · be7068a6
    Vladislav Zavialov authored
    During parsing, GHC collects lexical information about AST nodes and
    stores it in a map. It is needed to faithfully restore original source
    code, e.g. compare these expressions:
    	a =  b
    	a  = b
    The position of the equality sign is not recorded in the AST, so it must
    be stored elsewhere.
    This system is described in Note [Api annotations].
    Before this patch, the mapping was represented by:
    	Map (SrcSpan, AnnKeywordId) SrcSpan
    After this patch, the mapping is represented by:
    	Map (RealSrcSpan, AnnKeywordId) RealSrcSpan
    The motivation behind this change is to avoid using the Ord SrcSpan
    instance (required by Map here), as it interferes with #17632 (see the
    discussion there).
    SrcSpan is isomorphic to  Either String RealSrcSpan,  but we shouldn't
    use those strings as Map keys. Those strings are intended as hints to
    the user, e.g. "<interactive>" or "<compiler-generated code>", so they
    are not a valid way to identify nodes in the source code.
T12417.stdout 3.87 KB