[clang][Sema] Remove irrelevant diagnostics from constraint satisfaction failure

BEFORE this patch, when clang handles constraints like C1 || C2 where C1 evaluates to false and C2 evaluates to true, it emitted irrelevant diagnostics about the falsity of C1.
This patch removes the irrelevant diagnostic information generated during the evaluation of C1 if C2 evaluates to true.

Fixes https://github.com/llvm/llvm-project/issues/54678

Reviewed By: erichkeane
Differential Revision: https://reviews.llvm.org/D157526

clang/docs/ReleaseNotes.rst

@@ -169,6 +169,9 @@ Improvements to Clang's diagnostics
   Also clang no longer emits false positive warnings about the output length of
   ``%g`` format specifier and about ``%o, %x, %X`` with ``#`` flag.
 - Clang now emits ``-Wcast-qual`` for functional-style cast expressions.
+- Clang no longer emits irrelevant notes about unsatisfied constraint expressions
+  on the left-hand side of ``||`` when the right-hand side constraint is satisfied.
+  (`#54678: <https://github.com/llvm/llvm-project/issues/54678>`_).
 
 Bug Fixes in This Version
 -------------------------

clang/lib/Sema/SemaConcept.cpp

@@ -185,6 +185,7 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
   ConstraintExpr = ConstraintExpr->IgnoreParenImpCasts();
 
   if (LogicalBinOp BO = ConstraintExpr) {
+    auto EffectiveDetailEnd = Satisfaction.Details.end();
     ExprResult LHSRes = calculateConstraintSatisfaction(
         S, BO.getLHS(), Satisfaction, Evaluator);
 
@@ -218,6 +219,19 @@ calculateConstraintSatisfaction(Sema &S, const Expr *ConstraintExpr,
     if (RHSRes.isInvalid())
       return ExprError();
 
+    bool IsRHSSatisfied = Satisfaction.IsSatisfied;
+    // Current implementation adds diagnostic information about the falsity
+    // of each false atomic constraint expression when it evaluates them.
+    // When the evaluation results to `false || true`, the information
+    // generated during the evaluation of left-hand side is meaningless
+    // because the whole expression evaluates to true.
+    // The following code removes the irrelevant diagnostic information.
+    // FIXME: We should probably delay the addition of diagnostic information
+    // until we know the entire expression is false.
+    if (BO.isOr() && IsRHSSatisfied)
+      Satisfaction.Details.erase(EffectiveDetailEnd,
+                                 Satisfaction.Details.end());
+
     return BO.recreateBinOp(S, LHSRes, RHSRes);
   }
 

clang/test/SemaTemplate/concepts.cpp

@@ -994,3 +994,40 @@ void test_params() {
 }
 
 }
+
+namespace GH54678 {
+template<class>
+concept True = true;
+
+template<class>
+concept False = false; // expected-note 9 {{'false' evaluated to false}}
+
+template<class>
+concept Irrelevant = false;
+
+template <typename T>
+concept ErrorRequires = requires(ErrorRequires auto x) { x; }; // expected-error {{unknown type name 'ErrorRequires'}}
+
+template<class T> void aaa(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires (False<T> || False<T>) || False<T> {} // expected-note 3 {{'int' does not satisfy 'False'}}
+template<class T> void bbb(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires (False<T> || False<T>) && True<T> {} // expected-note 2 {{'long' does not satisfy 'False'}}
+template<class T> void ccc(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires (True<T> || Irrelevant<T>) && False<T> {} // expected-note {{'unsigned long' does not satisfy 'False'}}
+template<class T> void ddd(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires (Irrelevant<T> || True<T>) && False<T> {} // expected-note {{'int' does not satisfy 'False'}}
+template<class T> void eee(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires (Irrelevant<T> || Irrelevant<T> || True<T>) && False<T> {} // expected-note {{'long' does not satisfy 'False'}}
+
+template<class T> void fff(T t) // expected-note {{candidate template ignored: constraints not satisfied}}
+requires((ErrorRequires<T> || False<T> || True<T>) && False<T>) {} // expected-note {{'unsigned long' does not satisfy 'False'}}
+
+void test() {
+    aaa(42); // expected-error {{no matching function}}
+    bbb(42L); // expected-error{{no matching function}}
+    ccc(42UL); // expected-error {{no matching function}}
+    ddd(42); // expected-error {{no matching function}}
+    eee(42L); // expected-error {{no matching function}}
+    fff(42UL); // expected-error {{no matching function}}
+}
+}