[PATCH] D155610: [Clang][ExprConstant] Print integer instead of character on static assertion failure

[Takuya Shimizu via Phabricator via cfe-commits]

hazohelet added a comment.

Thanks everyone for the comments!



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Comment at: clang/test/Lexer/cxx1z-trigraphs.cpp:24
 // expected-error at 11 {{}} expected-warning at 11 {{trigraph ignored}}
-// expected-error at 13 {{failed}} expected-warning at 13 {{trigraph ignored}} expected-note at 13 {{evaluates to ''?' == '#''}}
+// expected-error at 13 {{failed}} expected-warning at 13 {{trigraph ignored}} expected-note at 13 {{evaluates to '63 == 35'}}
 // expected-error at 16 {{}}
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cor3ntin wrote:
> tahonermann wrote:
> > aaron.ballman wrote:
> > > I think the original diagnostic was actually more understandable as it relates more closely to what's written in the static assertion. I could imagine something like `evaluates to '?' (63) == '#' (35)` would also be reasonable.
> > I agree. I would also be ok with printing the integer value as primary with the character as secondary:
> >   evaluates to 63 ('?') == 35 ('#')
> > 
> > There are two kinds of non-printable characters:
> >   # Control characters (including new-line)
> >   # character values that don't correspond to a character (e.g., lone trailing characters or invalid code unit values).
> > For the first case, I would support printing them as either C escapes or universal-character-names. e.g.,
> >   evaluates to 0 ('\0') == 1 (\u0001)
> > For the second case, I would support printing them as C hex escapes. e.g, 
> >   evaluates to -128 ('\x80') == -123 ('\x85')
> > 
> > 
> > For the first case, I would support printing them as either C escapes or universal-character-names. e.g.,
> 
> As mentioned before, we should be consistent with what we do for diagnostics messages in general - (`ie `pushEscapedString`).
> I check and we already do that. https://godbolt.org/z/doah9YGMT
> 
> Question is, why do we sometimes don't?
> Note that in general i don't have an opinion about displaying the value of characters literal _in addition_ of the character itself, it seems like a good thing)
The character escape in the current error message is handled in `CharacterLiteral::print` (https://github.com/llvm/llvm-project/blob/fcb6a9c07cf7a2bc63d364e3b7f60aaadadd57cc/clang/lib/AST/Expr.cpp#L1064-L1083), and the reason for `'\0'` being escaped to `\x00` and `'\u{9}'` escaped to `\t` is that `escapeCStyle` does not escape null character (https://github.com/llvm/llvm-project/blob/c1c86f9eae73786bcdacddaab248817c4f176935/clang/include/clang/Basic/CharInfo.h#L174-L200).
`pushEscapedString` does not escape whitespace characters, so we should use `escapeCStyle` if we are to use c-style escape for them.


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https://reviews.llvm.org/D155610