Merge 2019-07 CWG Motion 16

P1823R0 Remove contracts from C++20

Fixes #2996.

Author: zygoloid

source/basic.tex

@@ -618,14 +618,6 @@
 that is, the default argument or default template argument
 is subject to the requirements described in this paragraph (recursively); and
 
-\item if \tcode{D} invokes a function with a precondition,
-or is a function
-that contains an assertion or has a contract condition\iref{dcl.attr.contract},
-it is \impldef{consistency of build level and violation continuation mode}
-under which conditions all definitions of \tcode{D}
-shall be translated using the same build level
-and violation continuation mode; and
-
 \item if \tcode{D} is a class with an implicitly-declared
 constructor (\ref{class.default.ctor}, \ref{class.copy.ctor}),
 it is as if the constructor was

source/classes.tex

@@ -562,8 +562,7 @@
 \begin{itemize}
 \item function body\iref{dcl.fct.def.general},
 \item default argument\iref{dcl.fct.default},
-\item \grammarterm{noexcept-specifier}\iref{except.spec},
-\item contract condition\iref{dcl.attr.contract}, or
+\item \grammarterm{noexcept-specifier}\iref{except.spec}, or
 \item default member initializer
 \end{itemize}
 within the \grammarterm{member-specification} of the class.
@@ -4105,45 +4104,6 @@
 A \tcode{consteval} virtual function shall not be overridden by
 a virtual function that is not \tcode{consteval}.
 
-\pnum
-If an overriding function specifies contract conditions\iref{dcl.attr.contract},
-it shall specify the same list of contract conditions as
-its overridden functions;
-no diagnostic is required
-if corresponding conditions will always evaluate to the same value.
-Otherwise, it is considered to have
-the list of contract conditions from one of its overridden functions;
-the names in the contract conditions are bound,
-and the semantic constraints are checked,
-at the point where the contract conditions appear.
-Given a virtual function \tcode{f}
-with a contract condition that odr-uses \tcode{*this}\iref{basic.def.odr},
-the class of which \tcode{f} is a direct member
-shall be be an unambiguous and accessible base class of any class
-in which \tcode{f} is overridden.
-If a function overrides more than one function,
-all of the overridden functions shall have
-the same list of contract conditions\iref{dcl.attr.contract};
-no diagnostic is required
-if corresponding conditions will always evaluate to the same value.
-\begin{example}
-\begin{codeblock}
-struct A {
-  virtual void g() [[expects: x == 0]];
-  int x = 42;
-};
-
-int x = 42;
-struct B {
-  virtual void g() [[expects: x == 0]];
-}
-
-struct C : A, B {
-  virtual void g();             // error: preconditions of overridden functions are not the same
-};
-\end{codeblock}
-\end{example}
-
 \rSec2[class.abstract]{Abstract classes}%
 
 \pnum

source/compatibility.tex

@@ -2124,7 +2124,6 @@
 \tcode{<bit>},
 \tcode{<compare>},
 \tcode{<concepts>},
-\tcode{<contract>},
 \tcode{<coroutine>},
 \tcode{<ranges>},
 \tcode{<span>},