Merge 2021-10 LWG Motion 4

P2418R2 Add support for std::generator-like types to std::format

Author: tkoeppe

source/compatibility.tex

@@ -76,6 +76,26 @@
                                                         // previously threw \tcode{format_error}
 \end{codeblock}
 
+\diffref{format}
+\change
+Signature changes: \tcode{format}, \tcode{format_to}, \tcode{format_to_n},
+\tcode{formatted_size}.
+\rationale
+Enable formatting of views
+that do not support iteration when const-qualified and
+are not copyable.
+\effect
+Valid \CppXX{} code that passes bit fields to formatting functions
+may become ill-formed. For example:
+\begin{codeblock}
+struct tiny {
+  int bit: 1;
+};
+
+auto t = tiny();
+std::format("{}", t.bit);       // ill-formed, previously returned \tcode{"0"}
+\end{codeblock}
+
 \rSec1[diff.cpp17]{\Cpp{} and ISO \CppXVII{}}
 
 \rSec2[diff.cpp17.general]{General}