From 3b49b51956bb0a1542146999ae9fd86d1707f63b Mon Sep 17 00:00:00 2001
From: Nicholas Bishop <nicholasbishop@google.com>
Date: Fri, 27 Feb 2026 14:22:08 -0500
Subject: [PATCH] Support bool template params (#6808)

https://github.com/carbon-language/carbon-lang/issues/6717
---
 toolchain/check/cpp/call.cpp                     | 16 +++++++++++++---
 .../interop/cpp/template/non_type_param.carbon   | 11 +++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/toolchain/check/cpp/call.cpp b/toolchain/check/cpp/call.cpp
index d849ecbcd0ff..ef5b9c2c5e40 100644
--- a/toolchain/check/cpp/call.cpp
+++ b/toolchain/check/cpp/call.cpp
@@ -177,17 +177,27 @@ static auto ConvertArgToTemplateArg(
         context.constant_values().GetConstantInstId(converted_inst_id);
     if (const_inst_id.has_value()) {
       if (param_type->isIntegerType()) {
+        const bool is_signed = param_type->isSignedIntegerOrEnumerationType();
         if (auto int_value =
                 context.insts().TryGetAs<SemIR::IntValue>(const_inst_id)) {
           const auto& ap_int = context.ints().Get(int_value->int_id);
-          const bool is_unsigned =
-              !param_type->isSignedIntegerOrEnumerationType();
           auto aps_int =
-              llvm::APSInt(ap_int, is_unsigned)
+              llvm::APSInt(ap_int, !is_signed)
                   .extOrTrunc(context.ast_context().getIntWidth(param_type));
           clang::TemplateArgument template_arg(context.ast_context(), aps_int,
                                                param_type);
           return clang::TemplateArgumentLoc(template_arg, template_loc);
+        } else if (auto bool_value =
+                       context.insts().TryGetAs<SemIR::BoolLiteral>(
+                           const_inst_id)) {
+          llvm::APInt ap_int(context.ast_context().getIntWidth(param_type),
+                             bool_value->value.ToBool(), is_signed);
+          auto aps_int =
+              llvm::APSInt(ap_int, !is_signed)
+                  .extOrTrunc(context.ast_context().getIntWidth(param_type));
+          auto template_arg = clang::TemplateArgument(context.ast_context(),
+                                                      aps_int, param_type);
+          return clang::TemplateArgumentLoc(template_arg, template_loc);
         }
       } else if (param_type->isFloatingType()) {
         if (auto float_value =
diff --git a/toolchain/check/testdata/interop/cpp/template/non_type_param.carbon b/toolchain/check/testdata/interop/cpp/template/non_type_param.carbon
index 74220204b59f..79d2dd4521b8 100644
--- a/toolchain/check/testdata/interop/cpp/template/non_type_param.carbon
+++ b/toolchain/check/testdata/interop/cpp/template/non_type_param.carbon
@@ -76,6 +76,17 @@ impl C as Core.ImplicitAs(i32) {
 }
 var s: Cpp.Simple({} as C) = Cpp.MakeSimple123();
 
+// --- bool.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+template<bool B> struct Struct {};
+Struct<true> MakeStruct() { return Struct<true>(); }
+''';
+
+var s: Cpp.Struct(true) = Cpp.MakeStruct();
+
 // --- float.carbon
 
 library "[[@TEST_NAME]]";