Detect recursive creation of generics #2366.

releasenotes.md

@@ -14,6 +14,7 @@
 - Reduce allocated Vmem for the compiler on 32 bit machines.
 - Bug causing a compiler error when parsing a broken lambda inside of an expression.
 - Fixed: regression in comments for `@deprecated` and `@pure`.
+- Detect recursive creation of generics #2366.
 
 ### Stdlib changes
 - Add `==` to `Pair`, `Triple` and TzDateTime. Add print to `Pair` and `Triple`.

src/compiler/compiler_internal.h

@@ -48,6 +48,7 @@ typedef uint16_t FileId;
 #define MAX_BITSTRUCT 0x1000
 #define MAX_MEMBERS ((StructIndex)1) << 15
 #define MAX_ALIGNMENT ((ArrayIndex)(((uint64_t)2) << 28))
+#define MAX_GENERIC_DEPTH 32
 #define MAX_PRIORITY 0xFFFF
 #define MAX_TYPE_SIZE UINT32_MAX
 #define MAX_GLOBAL_DECL_STACK (65536)
@@ -1931,6 +1932,7 @@ typedef struct
 	Linking linking;
 	GlobalContext context;
 	const char *obj_output;
+	int generic_depth;
 } CompilerState;
 
 extern CompilerState compiler;

src/compiler/sema_types.c

@@ -450,8 +450,14 @@ INLINE bool sema_resolve_generic_type(SemaContext *context, TypeInfo *type_info)
 	ASSERT_SPAN(inner, inner->resolve_status == RESOLVE_NOT_DONE);
 
 	bool was_recursive = false;
+	if (compiler.generic_depth >= MAX_GENERIC_DEPTH)
+	{
+		RETURN_SEMA_ERROR(type_info, "Generic resolution of this type has become deeply nested, it was aborted after reaching %d recursions.", compiler.generic_depth);
+	}
+	compiler.generic_depth++;
 	Decl *type = sema_analyse_parameterized_identifier(context, inner->unresolved.path, inner->unresolved.name,
 	                                                   inner->span, type_info->generic.params, &was_recursive);
+	compiler.generic_depth--;
 	if (!decl_ok(type)) return false;
 	if (!sema_analyse_decl(context, type)) return false;
 	type_info->type = type->type;

test/test_suite/generic/recursive_generic.c3

@@ -0,0 +1,14 @@
+module test;
+import test1;
+
+fn int main() => 0;
+
+Aa {int} a;
+
+module test1 {Type};
+import test2;
+alias Cc = Aa {Bb {Type}}; // #error: Generic resolution of this type has become deeply nested
+struct Aa {Type a;}
+
+module test2 {Type};
+struct Bb {Type b;}