[PATCH] D103380: [C++20] Support for lambdas in unevaluated context

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin created this revision.
cor3ntin requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Partially implement P0315R4.

This patch allow lambda in unevaluated context.
It does not implement temp.deduct/9.

This is a rewrite of https://reviews.llvm.org/D66481 that did
not see progress over the past 2 years.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103380

Files:
  clang/lib/Sema/SemaConcept.cpp
  clang/lib/Sema/SemaExpr.cpp
  clang/test/CXX/expr/expr.prim/expr.prim.lambda/p2-unevaluated.cpp
  clang/test/SemaCXX/anonymous-struct.cpp
  clang/www/cxx_status.html


Index: clang/www/cxx_status.html
===================================================================
--- clang/www/cxx_status.html
+++ clang/www/cxx_status.html
@@ -1011,7 +1011,7 @@
     <tr>
       <td>Lambdas in unevaluated contexts</td>
       <td><a href="https://wg21.link/p0315r4">P0315R4</a></td>
-      <td class="none" align="center">No</td>
+      <td class="partial" align="center">Clang 13</td>
     </tr>
     <!-- Jacksonville papers -->
     <tr>
Index: clang/test/SemaCXX/anonymous-struct.cpp
===================================================================
--- clang/test/SemaCXX/anonymous-struct.cpp
+++ clang/test/SemaCXX/anonymous-struct.cpp
@@ -49,7 +49,7 @@
 : B { // expected-note {{type is not C-compatible due to this base class}}
 } C; // expected-note {{type is given name 'C' for linkage purposes by this typedef declaration}}
 
-#if __cplusplus > 201703L
+#if __cplusplus > 201703L && __cplusplus < 202002L
 typedef struct { // expected-warning {{anonymous non-C-compatible type given name for linkage purposes by typedef declaration; add a tag name here}}
   static_assert([]{ return true; }()); // expected-note {{type is not C-compatible due to this lambda expression}}
 } Lambda1; // expected-note {{type is given name 'Lambda1' for linkage purposes by this typedef declaration}}
Index: clang/test/CXX/expr/expr.prim/expr.prim.lambda/p2-unevaluated.cpp
===================================================================
--- /dev/null
+++ clang/test/CXX/expr/expr.prim/expr.prim.lambda/p2-unevaluated.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -std=c++20 %s -verify
+// expected-no-diagnostics
+
+template<auto> struct Nothing {};
+
+template<typename T>
+concept True = [] { return true; }();
+
+static_assert(True<int>);
+
+using x = decltype([] { return 0;}());
+
+Nothing<[]() { return 0; }()> nothing;
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -16657,8 +16657,8 @@
 
   if (!Rec.Lambdas.empty()) {
     using ExpressionKind = ExpressionEvaluationContextRecord::ExpressionKind;
-    if (Rec.ExprContext == ExpressionKind::EK_TemplateArgument || Rec.isUnevaluated() ||
-        (Rec.isConstantEvaluated() && !getLangOpts().CPlusPlus17)) {
+    if (!getLangOpts().CPlusPlus20 && (Rec.ExprContext == ExpressionKind::EK_TemplateArgument || Rec.isUnevaluated() ||
+        (Rec.isConstantEvaluated() && !getLangOpts().CPlusPlus17))) {
       unsigned D;
       if (Rec.isUnevaluated()) {
         // C++11 [expr.prim.lambda]p2:
Index: clang/lib/Sema/SemaConcept.cpp
===================================================================
--- clang/lib/Sema/SemaConcept.cpp
+++ clang/lib/Sema/SemaConcept.cpp
@@ -41,9 +41,11 @@
       LHS = BO->getLHS();
       RHS = BO->getRHS();
     } else if (auto *OO = dyn_cast<CXXOperatorCallExpr>(E)) {
-      Op = OO->getOperator();
-      LHS = OO->getArg(0);
-      RHS = OO->getArg(1);
+        if(OO->getNumArgs() == 2) {
+          Op = OO->getOperator();
+          LHS = OO->getArg(0);
+          RHS = OO->getArg(1);
+      }
     }
   }
 


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