Mark de Wever 402eb2ef09 [libc++][format] Improves diagnostics.
Improves both the compile-time and run-time errors.
At compile-time it does a bit more work to get more specific errors.
This could be done at run-time too, but that has a performance penalty.
Since it's expected most use-cases use format* instead of vformat* the
compile-time errors are more common.

For example when using

  std::format_to("{:-c}", 42);

Before compile output would contain

  std::__throw_format_error("The format-spec should consume the input or end with a '}'");

Now it contains

  std::__throw_format_error("The format specifier does not allow the sign option");

Given a better indication the sign option is not allowed. Note the
output is still not user-friendly; C++ doesn't have good facilities to
generate nice messages from the library.

In general all messages have been reviewed and improved, using a more
consistent style and using less terms used in the standard. For example

  format-spec -> format specifier
  arg-id -> argument index

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D152624
2023-07-18 21:11:12 +02:00
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