Sema: do not immediately destroy failed generic instantiation

Closes #12535
Closes #12765
Closes #12927

1 files changed, 27 insertions, 0 deletions

diff --git a/test/cases/compile_errors/generic_instantiation_failure.zig b/test/cases/compile_errors/generic_instantiation_failure.zig
new file mode 100644
index 0000000000..42e4c4e8c8
--- /dev/null
+++ b/test/cases/compile_errors/generic_instantiation_failure.zig
@@ -0,0 +1,27 @@
+fn List(comptime Head: type, comptime Tail: type) type {
+    return union {
+        const Self = @This();
+        head: Head,
+        tail: Tail,
+
+        fn AppendReturnType(comptime item: anytype) type {
+            return List(Head, List(@TypeOf(item), void));
+        }
+    };
+}
+
+fn makeList(item: anytype) List(@TypeOf(item), void) {
+    return List(@TypeOf(item), void){ .head = item };
+}
+
+pub export fn entry() void {
+    @TypeOf(makeList(42)).AppendReturnType(64);
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :18:43: error: value of type 'type' ignored
+// :18:43: note: all non-void values must be used
+// :18:43: note: this error can be suppressed by assigning the value to '_'