From e84e23f7ec70e925d17495cae109d0df5bead52f Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Tue, 20 Jan 2026 01:04:12 +0100
Subject: [PATCH] Fix Using @if with methods with generic params only inferred
 from the parent type fails #2770

---
 src/compiler/compiler_internal.h              |  1 +
 src/compiler/sema_name_resolution.c           | 15 +++++++++++
 src/compiler/sema_passes.c                    | 27 +++++++++++++++++++
 .../generic/generic_with_method_ad_hoc.c3t    | 11 ++++++++
 4 files changed, 54 insertions(+)
 create mode 100644 test/test_suite/generic/generic_with_method_ad_hoc.c3t

diff --git a/src/compiler/compiler_internal.h b/src/compiler/compiler_internal.h
index ccf7abb83..d92c40b0e 100644
--- a/src/compiler/compiler_internal.h
+++ b/src/compiler/compiler_internal.h
@@ -2567,6 +2567,7 @@ Decl *sema_find_label_symbol_anywhere(SemaContext *context, const char *symbol);
 Decl *sema_find_local(SemaContext *context, const char *symbol);
 Decl *sema_resolve_symbol(SemaContext *context, const char *symbol, Path *path, SourceSpan span);
 Decl *sema_resolve_parameterized_symbol(SemaContext *context, const char *symbol, Path *path, SourceSpan span);
+Decl *sema_resolve_maybe_parameterized_symbol(SemaContext *context, const char *symbol, Path *path, SourceSpan span);
 BoolErr sema_symbol_is_defined_in_scope(SemaContext *c, const char *symbol);
 
 bool sema_resolve_array_like_len(SemaContext *context, TypeInfo *type_info, ArraySize *len_ref);
diff --git a/src/compiler/sema_name_resolution.c b/src/compiler/sema_name_resolution.c
index 588f3585b..1134cc3f2 100644
--- a/src/compiler/sema_name_resolution.c
+++ b/src/compiler/sema_name_resolution.c
@@ -1190,6 +1190,21 @@ Decl *sema_resolve_parameterized_symbol(SemaContext *context, const char *symbol
 	return resolve.found;
 }
 
+Decl *sema_resolve_maybe_parameterized_symbol(SemaContext *context, const char *symbol, Path *path, SourceSpan span)
+{
+	NameResolve resolve = {
+		.path = path,
+		.span = span,
+		.symbol = symbol,
+		.is_parameterized = true,
+		.suppress_error = true
+	};
+	if (!sema_resolve_symbol_common(context, &resolve)) return NULL;
+	Decl *found = resolve.found;
+	if (!decl_ok(found)) return NULL;
+	return resolve.found;
+}
+
 bool sema_parameterized_type_is_found(SemaContext *context, Path *decl_path, const char *name, SourceSpan span)
 {
 	NameResolve name_resolve = {
diff --git a/src/compiler/sema_passes.c b/src/compiler/sema_passes.c
index a60024e27..99098c080 100644
--- a/src/compiler/sema_passes.c
+++ b/src/compiler/sema_passes.c
@@ -163,11 +163,38 @@ FOUND_ALIAS:
 	DEBUG_LOG("Pass finished processing %d import(s) with %d error(s).", total_import_count, compiler.context.errors_found);
 }
 
+static bool sema_check_if_implicit_generic(SemaContext *context, Decl *decl)
+{
+	if (!decl->func_decl.type_parent) return false;
+	TypeInfo *typedecl = type_infoptr(decl->func_decl.type_parent);
+	Decl *d = NULL;
+	if (typedecl->resolve_status == RESOLVE_DONE)
+	{
+		CanonicalType *type = typedecl->type->canonical;
+		if (!type_is_user_defined(type)) return false;
+		d = type->decl;
+	}
+	else if (typedecl->kind == TYPE_INFO_IDENTIFIER && typedecl->subtype == TYPE_COMPRESSED_NONE)
+	{
+		d = sema_resolve_maybe_parameterized_symbol(context, typedecl->unresolved.name, typedecl->unresolved.path, typedecl->span);
+	}
+	return d && d->is_template;
+}
+
 void unit_register_optional_global_decl(CompilationUnit *unit, Decl *decl)
 {
 	SemaContext context;
 	sema_context_init(&context, unit);
 	if (decl->is_templated) context.generic_instance = declptr(decl->instance_id);
+	if (!decl->is_templated && (decl->decl_kind == DECL_MACRO || decl->decl_kind == DECL_FUNC))
+	{
+		if (sema_check_if_implicit_generic(&context, decl))
+		{
+			unit_register_global_decl(unit, decl);
+			sema_context_destroy(&context);
+			return;
+		}
+	}
 	if (sema_decl_if_cond(&context, decl))
 	{
 		unit_register_global_decl(unit, decl);
diff --git a/test/test_suite/generic/generic_with_method_ad_hoc.c3t b/test/test_suite/generic/generic_with_method_ad_hoc.c3t
new file mode 100644
index 000000000..b66fc746c
--- /dev/null
+++ b/test/test_suite/generic/generic_with_method_ad_hoc.c3t
@@ -0,0 +1,11 @@
+import std;
+struct Foo <Type> { int a; }
+
+fn void Foo.test(self) @if(Type.sizeof > 4)
+{  }
+
+fn int main()
+{
+	Foo{int} x;
+	return 0;
+}