[PATCH] Fix makeFileCharRange for macro arguments in the presence of nested macro calls.

[Manuel Klimek]

Hi doug.gregor,

Added tests that show the problems:
1. isAt(Start|End)OfMacroExpansion did not work correctly for nested macro
   calls; consider
   #define M(x) x
   #define N(x) x
   N(f(M(i)))
   Here getSourceText would return "M(f(M(i)))" for the token location of 'i',
   as makeFileCharRange would consider 'i' to be at the start of the macro.
   The problem is that getDecomposedLoc in this case returns the offset from
   the inner call to 'M', and I have not found a way to get the offset from
   'N' easily, as this information seems to be incrementally overwritten during
   preprocessing.
   The solution is to instead take the location before / after the examined
   location and check whether its expansion location is the same as the
   expansion location of the examined location. If this is the case, the
   location before / after is not the first / last token of the macro expansion.

2. makeFileCharRange only considered the outermost layer of macro expansion,
   thus not returning the widest possible range if the outermost expansion
   was not fully describing the range.
   After fixing (1), this would lead to getSourceText returning an empty
   string instead of "M(i)".

Note that I'm still not sure I'm entirely happy with this implementation.
So far I have not found a good way to figure out whether the location
is good to call getLocWithOffset(-1) or getLocWithOffset(tokLen + 1) on.
Especially for the latter, the check for SM.isLocalSourceLocation(...) seems
to work, but doesn't seem like the right solution. Any hints for a better
solution would be highly welcome.

http://llvm-reviews.chandlerc.com/D767

Files:
  lib/Lex/Lexer.cpp
  unittests/Lex/LexerTest.cpp
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