From c71444e7a0c3d1c4f371af48e3804fe7da5ce62b Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Tue, 16 Sep 2025 14:10:23 +0200
Subject: [PATCH] Compile time switch over type would not correctly compare
 function pointer types.

---
 lib/std/core/builtin.c3                       |  2 +-
 releasenotes.md                               |  1 +
 src/compiler/types.c                          |  4 +
 test/test_suite/compile_time/ct_switch_fn.c3t | 92 +++++++++++++++++++
 4 files changed, 98 insertions(+), 1 deletion(-)
 create mode 100644 test/test_suite/compile_time/ct_switch_fn.c3t

diff --git a/lib/std/core/builtin.c3 b/lib/std/core/builtin.c3
index 553e47ab5..8c52ea71f 100644
--- a/lib/std/core/builtin.c3
+++ b/lib/std/core/builtin.c3
@@ -108,7 +108,7 @@ macro anycast(any v, $Type) @builtin
 	return ($Type*)v.ptr;
 }
 
-macro bool @assignable_to(#foo, $Type) @const @builtin @deprecated("use '$define($Type x = #foo)'") => $defined(*&&($Type){} = #foo);
+macro bool @assignable_to(#foo, $Type) @const @builtin @deprecated("use '$defined($Type x = #foo)'") => $defined(*&&($Type){} = #foo);
 
 macro @addr(#val) @builtin
 {
diff --git a/releasenotes.md b/releasenotes.md
index 9194b3b37..540ac56ab 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -22,6 +22,7 @@
 - `??` with void results on both sides cause a compiler crash #2472.
 - Stack object size limit error on a static object. #2476
 - Compiler segfault when modifying variable using an inline assembly block inside defer #2450.
+- Compile time switch over type would not correctly compare function pointer types.
 
 ### Stdlib changes
 - Added generic `InterfaceList` to store a list of values that implement a specific interface
diff --git a/src/compiler/types.c b/src/compiler/types.c
index 51bdfa04e..a178b45da 100644
--- a/src/compiler/types.c
+++ b/src/compiler/types.c
@@ -1598,6 +1598,10 @@ bool type_is_subtype(Type *type, Type *possible_subtype)
 	{
 		possible_subtype = possible_subtype->canonical;
 		if (type == possible_subtype) return true;
+		if (type->type_kind == TYPE_FUNC_PTR && possible_subtype->type_kind == TYPE_FUNC_PTR)
+		{
+			return type->pointer->function.prototype->raw_type == possible_subtype->pointer->function.prototype->raw_type;
+		}
 		possible_subtype = type_find_parent_type(possible_subtype);
 	}
 	return false;
diff --git a/test/test_suite/compile_time/ct_switch_fn.c3t b/test/test_suite/compile_time/ct_switch_fn.c3t
new file mode 100644
index 000000000..01df5bb88
--- /dev/null
+++ b/test/test_suite/compile_time/ct_switch_fn.c3t
@@ -0,0 +1,92 @@
+// #target: macos-x64
+module test;
+import std;
+
+alias Foo = fn void();
+
+macro @test(#foo)
+{
+	$switch $typeof(#foo):
+	$case Foo:
+	io::printn("Hello");
+	$default:
+	io::printn($typeof(#foo).nameof);
+	$endswitch
+}
+fn void tester() {}
+fn int main(String[] args)
+{
+	@test(&tester);
+	return 0;
+}
+/* #expect: test.ll
+
+define i32 @test.main(ptr %0, i64 %1) #0 {
+entry:
+  %args = alloca %"char[][]", align 8
+  %len = alloca i64, align 8
+  %error_var = alloca i64, align 8
+  %retparam = alloca i64, align 8
+  %error_var2 = alloca i64, align 8
+  %error_var8 = alloca i64, align 8
+  store ptr %0, ptr %args, align 8
+  %ptradd = getelementptr inbounds i8, ptr %args, i64 8
+  store i64 %1, ptr %ptradd, align 8
+  %2 = call ptr @std.io.stdout()
+  %3 = call i64 @std.io.File.write(ptr %retparam, ptr %2, ptr @.str, i64 5)
+  %not_err = icmp eq i64 %3, 0
+  %4 = call i1 @llvm.expect.i1(i1 %not_err, i1 true)
+  br i1 %4, label %after_check, label %assign_optional
+
+assign_optional:                                  ; preds = %entry
+  store i64 %3, ptr %error_var, align 8
+  br label %guard_block
+
+after_check:                                      ; preds = %entry
+  br label %noerr_block
+
+guard_block:                                      ; preds = %assign_optional
+  br label %voiderr
+
+noerr_block:                                      ; preds = %after_check
+  %5 = load i64, ptr %retparam, align 8
+  store i64 %5, ptr %len, align 8
+  %6 = call i64 @std.io.File.write_byte(ptr %2, i8 zeroext 10)
+  %not_err3 = icmp eq i64 %6, 0
+  %7 = call i1 @llvm.expect.i1(i1 %not_err3, i1 true)
+  br i1 %7, label %after_check5, label %assign_optional4
+
+assign_optional4:                                 ; preds = %noerr_block
+  store i64 %6, ptr %error_var2, align 8
+  br label %guard_block6
+
+after_check5:                                     ; preds = %noerr_block
+  br label %noerr_block7
+
+guard_block6:                                     ; preds = %assign_optional4
+  br label %voiderr
+
+noerr_block7:                                     ; preds = %after_check5
+  %8 = call i64 @std.io.File.flush(ptr %2)
+  %not_err9 = icmp eq i64 %8, 0
+  %9 = call i1 @llvm.expect.i1(i1 %not_err9, i1 true)
+  br i1 %9, label %after_check11, label %assign_optional10
+
+assign_optional10:                                ; preds = %noerr_block7
+  store i64 %8, ptr %error_var8, align 8
+  br label %guard_block12
+
+after_check11:                                    ; preds = %noerr_block7
+  br label %noerr_block13
+
+guard_block12:                                    ; preds = %assign_optional10
+  br label %voiderr
+
+noerr_block13:                                    ; preds = %after_check11
+  %10 = load i64, ptr %len, align 8
+  %add = add i64 %10, 1
+  br label %voiderr
+
+voiderr:                                          ; preds = %noerr_block13, %guard_block12, %guard_block6, %guard_block
+  ret i32 0
+}