From d92a981083ed96947395c5aa48812a666b8381c7 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Tue, 8 Sep 2026 23:36:36 +0000
Subject: [PATCH] Add explicit testing for use of non-constant template
 arguments. (#7735)

Also move another template test into the template/ subdirectory.
---
 .../testdata/generic/template/argument.carbon | 77 +++++++++++++++++++
 .../dependence.carbon}                        |  4 +-
 2 files changed, 79 insertions(+), 2 deletions(-)
 create mode 100644 toolchain/check/testdata/generic/template/argument.carbon
 rename toolchain/check/testdata/generic/{template_dependence.carbon => template/dependence.carbon} (99%)

diff --git a/toolchain/check/testdata/generic/template/argument.carbon b/toolchain/check/testdata/generic/template/argument.carbon
new file mode 100644
index 000000000000..f3eb9334d353
--- /dev/null
+++ b/toolchain/check/testdata/generic/template/argument.carbon
@@ -0,0 +1,77 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/destroy.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/generic/template/argument.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/generic/template/argument.carbon
+
+// --- constant_type_argument.carbon
+library "[[@TEST_NAME]]";
+
+fn F(template T: type, unused x: T) {}
+
+class X {}
+
+fn G(x: X) {
+  F((), ());
+  F({}, {});
+  F(X, {});
+  F(type, X);
+  F(X, x);
+}
+
+// --- constant_nontype_argument.carbon
+library "[[@TEST_NAME]]";
+
+fn F(template T: type, unused template X: T) {}
+
+class X {}
+
+fn G() {
+  F((), ());
+  F({}, {});
+  F(X, {});
+  F(type, X);
+}
+
+// --- fail_non_constant_type_argument.carbon
+library "[[@TEST_NAME]]";
+
+class Y {}
+let T: type = Y;
+
+fn F(template T: type, unused y: T) {}
+
+fn H(y: Y) {
+  // CHECK:STDERR: fail_non_constant_type_argument.carbon:[[@LINE+7]]:3: error: argument for generic parameter is not a compile-time constant [CompTimeArgumentNotConstant]
+  // CHECK:STDERR:   F(T, y);
+  // CHECK:STDERR:   ^~~~~~~
+  // CHECK:STDERR: fail_non_constant_type_argument.carbon:[[@LINE-6]]:6: note: initializing generic parameter `T` declared here [InitializingGenericParam]
+  // CHECK:STDERR: fn F(template T: type, unused y: T) {}
+  // CHECK:STDERR:      ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  F(T, y);
+}
+
+// --- fail_non_constant_nontype_argument.carbon
+library "[[@TEST_NAME]]";
+
+class Y {}
+
+fn F(unused template X: Y) {}
+
+fn H(y: Y) {
+  // CHECK:STDERR: fail_non_constant_nontype_argument.carbon:[[@LINE+7]]:3: error: argument for generic parameter is not a compile-time constant [CompTimeArgumentNotConstant]
+  // CHECK:STDERR:   F(y);
+  // CHECK:STDERR:   ^~~~
+  // CHECK:STDERR: fail_non_constant_nontype_argument.carbon:[[@LINE-6]]:13: note: initializing generic parameter `X` declared here [InitializingGenericParam]
+  // CHECK:STDERR: fn F(unused template X: Y) {}
+  // CHECK:STDERR:             ^~~~~~~~~~~~~
+  // CHECK:STDERR:
+  F(y);
+}
diff --git a/toolchain/check/testdata/generic/template_dependence.carbon b/toolchain/check/testdata/generic/template/dependence.carbon
similarity index 99%
rename from toolchain/check/testdata/generic/template_dependence.carbon
rename to toolchain/check/testdata/generic/template/dependence.carbon
index 919564b57a4b..5ca963383807 100644
--- a/toolchain/check/testdata/generic/template_dependence.carbon
+++ b/toolchain/check/testdata/generic/template/dependence.carbon
@@ -6,9 +6,9 @@
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
-// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/generic/template_dependence.carbon
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/generic/template/dependence.carbon
 // TIP: To dump output, run:
-// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/generic/template_dependence.carbon
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/generic/template/dependence.carbon
 
 // --- type.carbon