<format>: Fix STL internal check when formatting empty strings
#4243
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… internal check `_First < _Last` When `_First == _Last`, the iterator will compare equal to `default_sentinel_t` and the callsite `_Measure_string_prefix()` will do the right thing, we just need to avoid calling `_Decode_utf()` for an empty range. This will leave `_Next` as null, which is fine - we only need it when we increment the iterator. `_Measure_string_prefix_iterator_legacy` already appears to handle empty ranges correctly.
CaseyCarter
reviewed
Dec 6, 2023
| _Next = _Decode_utf(_First, _Last, _Val)._Next_ptr; | ||
| if (_First != _Last) { | ||
| _Next = _Decode_utf(_First, _Last, _Val)._Next_ptr; | ||
| } | ||
| } | ||
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| constexpr _Unicode_codepoint_iterator() = default; |
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Drive-by WTF: Why does line 364 check _Last == _Other._Last when line 363 say it's a precondition? Should we fix that in another PR?
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Good catch. I assume I wrote the INTERNAL_CHECK on a different side of a coffee break than the return statement :D
CaseyCarter
approved these changes
Dec 6, 2023
barcharcraz
approved these changes
Dec 7, 2023
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Fixes #4241. Test coverage will be provided by the upcoming libcxx update.
When
_First == _Last, the iterator will compare equal todefault_sentinel_tand the callsite_Measure_string_prefix()will do the right thing, we just need to avoid calling_Decode_utf()for an empty range. This will leave_Nextas null, which is fine - we only need it when we increment the iterator._Measure_string_prefix_iterator_legacyalready appears to handle empty ranges correctly.