1 files changed, 34 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 58614322f76..1485b80cf95 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2831,10 +2831,44 @@ static void collectConjunctionTerms(Expr *Clause,
   Terms.push_back(Clause);
 }
 
+// The ranges-v3 library uses an odd pattern of a top-level "||" with
+// a left-hand side that is value-dependent but never true. Identify
+// the idiom and ignore that term.
+static Expr *lookThroughRangesV3Condition(Preprocessor &PP, Expr *Cond) {
+  // Top-level '||'.
+  auto *BinOp = dyn_cast<BinaryOperator>(Cond->IgnoreParenImpCasts());
+  if (!BinOp) return Cond;
+
+  if (BinOp->getOpcode() != BO_LOr) return Cond;
+
+  // With an inner '==' that has a literal on the right-hand side.
+  Expr *LHS = BinOp->getLHS();
+  auto InnerBinOp = dyn_cast<BinaryOperator>(LHS->IgnoreParenImpCasts());
+  if (!InnerBinOp) return Cond;
+
+  if (InnerBinOp->getOpcode() != BO_EQ ||
+      !isa<IntegerLiteral>(InnerBinOp->getRHS()))
+    return Cond;
+
+  // If the inner binary operation came from a macro expansion named
+  // CONCEPT_REQUIRES or CONCEPT_REQUIRES_, return the right-hand side
+  // of the '||', which is the real, user-provided condition.
+  auto Loc = InnerBinOp->getExprLoc();
+  if (!Loc.isMacroID()) return Cond;
+
+  StringRef MacroName = PP.getImmediateMacroName(Loc);
+  if (MacroName == "CONCEPT_REQUIRES" || MacroName == "CONCEPT_REQUIRES_")
+    return BinOp->getRHS();
+
+  return Cond;
+}
+
 /// Find the failed subexpression within enable_if, and describe it
 /// with a string.
 static std::pair<Expr *, std::string>
 findFailedEnableIfCondition(Sema &S, Expr *Cond) {
+  Cond = lookThroughRangesV3Condition(S.PP, Cond);
+
   // Separate out all of the terms in a conjunction.
   SmallVector<Expr *, 4> Terms;
   collectConjunctionTerms(Cond, Terms);