Disambiguate types when they have the same name and need cast between each other.

releasenotes.md

@@ -88,6 +88,7 @@
 - Deprecated `@select` in favor of `???`.
 - Enum inference, like `Foo x = $eval("A")`, now works correctly for `$eval`.
 - Fix regression where files were added more than once. #2442
+- Disambiguate types when they have the same name and need cast between each other.
 
 ### Stdlib changes
 - Add `==` to `Pair`, `Triple` and TzDateTime. Add print to `Pair` and `Triple`.

src/compiler/compiler_internal.h

@@ -2584,6 +2584,9 @@ FunctionPrototype *type_get_resolved_prototype(Type *type);
 bool type_is_inner_type(Type *type);
 const char *type_to_error_string(Type *type);
 const char *type_quoted_error_string(Type *type);
+const char *type_quoted_error_string_with_path(Type *type);
+const char *type_error_string_maybe_with_path(Type *type, Type *other_type);
+const char *type_quoted_error_string_maybe_with_path(Type *type, Type *other_type);
 INLINE bool type_may_negate(Type *type);
 INLINE bool type_is_builtin(TypeKind kind);
 INLINE bool type_convert_will_trunc(Type *destination, Type *source);

src/compiler/sema_casts.c

@@ -727,21 +727,23 @@ static bool report_cast_error(CastContext *cc, bool may_cast_explicit)
 	}
 	if (may_cast_explicit)
 	{
+		Type *typeto = type_no_optional(to);
+		Type *from = type_no_optional(expr->type);
 		if (expr->type->canonical->type_kind == TYPE_DISTINCT
 			&& type_no_optional(to)->canonical->type_kind == TYPE_DISTINCT)
 		{
 			RETURN_CAST_ERROR(expr,
 					   "Implicitly casting %s to %s is not permitted. It's possible to do an explicit cast by placing '(%s)' before the expression. However, explicit casts between distinct types are usually not intended and are not safe.",
-					   type_quoted_error_string(type_no_optional(expr->type)),
-					   type_quoted_error_string(to),
-					   type_to_error_string(type_no_optional(to)));
+					   type_quoted_error_string_maybe_with_path(from, typeto),
+					   type_quoted_error_string_maybe_with_path(to, from),
+					   type_error_string_maybe_with_path(typeto, from));
 
 		}
 		RETURN_CAST_ERROR(expr,
 		           "Implicitly casting %s to %s is not permitted, but you may do an explicit cast by placing '(%s)' before the expression.",
-		           type_quoted_error_string(type_no_optional(expr->type)),
-		           type_quoted_error_string(to),
-		           type_to_error_string(type_no_optional(to)));
+		           type_quoted_error_string_maybe_with_path(from, typeto),
+				   type_quoted_error_string_maybe_with_path(to, from),
+				   type_error_string_maybe_with_path(typeto, from));
 	}
 	if (to->type_kind == TYPE_INTERFACE)
 	{

src/compiler/types.c

@@ -6,6 +6,7 @@
 
 
 static Type *flatten_raw_function_type(Type *type);
+static const char *type_to_error_string_with_path(Type *type);
 
 static struct
 {
@@ -99,6 +100,18 @@ Type *type_int_unsigned_by_bitsize(BitSize bit_size)
 	}
 }
 
+const char *type_quoted_error_string_maybe_with_path(Type *type, Type *other_type)
+{
+	if (!str_eq(type_no_optional(type)->name, type_no_optional(other_type)->name)) return type_quoted_error_string(type);
+	return type_quoted_error_string_with_path(type);
+}
+
+const char *type_error_string_maybe_with_path(Type *type, Type *other_type)
+{
+	if (!str_eq(type_no_optional(type)->name, type_no_optional(other_type)->name)) return type_to_error_string(type);
+	return type_to_error_string_with_path(type);
+}
+
 const char *type_quoted_error_string(Type *type)
 {
 	if (type->canonical != type)
@@ -108,6 +121,15 @@ const char *type_quoted_error_string(Type *type)
 	return str_printf("'%s'", type_to_error_string(type));
 }
 
+const char *type_quoted_error_string_with_path(Type *type)
+{
+	if (type->canonical != type)
+	{
+		return str_printf("'%s' (%s)", type_to_error_string_with_path(type), type_to_error_string_with_path(type->canonical));
+	}
+	return str_printf("'%s'", type_to_error_string_with_path(type));
+}
+
 void type_append_name_to_scratch(Type *type)
 {
 	type = type->canonical;
@@ -234,6 +256,7 @@ static void type_add_parent_to_scratch(Decl *decl)
 			return;
 	}
 }
+
 const char *type_to_error_string(Type *type)
 {
 	switch (type->type_kind)
@@ -301,6 +324,77 @@ const char *type_to_error_string(Type *type)
 	UNREACHABLE
 }
 
+static const char *type_to_error_string_with_path(Type *type)
+{
+	switch (type->type_kind)
+	{
+		case TYPE_POISONED:
+			return "poisoned";
+		case TYPE_VOID:
+		case TYPE_BOOL:
+		case ALL_INTS:
+		case ALL_FLOATS:
+		case TYPE_ANYFAULT:
+		case TYPE_UNTYPED_LIST:
+		case TYPE_ANY:
+		case TYPE_MEMBER:
+		case TYPE_WILDCARD:
+			return type->name;
+		case TYPE_ENUM:
+		case TYPE_CONST_ENUM:
+		case TYPE_TYPEDEF:
+		case TYPE_STRUCT:
+		case TYPE_UNION:
+		case TYPE_DISTINCT:
+		case TYPE_BITSTRUCT:
+		case TYPE_INTERFACE:
+		{
+			Decl *decl = type->decl;
+			const char *suffix = decl->unit->module->generic_suffix;
+			scratch_buffer_clear();
+			scratch_buffer_append(decl->unit->module->name->module);
+			scratch_buffer_append("::");
+			if (suffix || type_is_inner_type(type))
+			{
+				type_add_parent_to_scratch(decl);
+			}
+			scratch_buffer_append(decl->name);
+			if (suffix) scratch_buffer_append(suffix);
+			return scratch_buffer_copy();
+		}
+		case TYPE_FUNC_PTR:
+			type = type->pointer;
+			FALLTHROUGH;
+		case TYPE_FUNC_RAW:
+			if (!type->function.prototype) return type->name;
+			scratch_buffer_clear();
+			scratch_buffer_append("fn ");
+			type_append_func_to_scratch(type->function.prototype);
+			return scratch_buffer_copy();
+		case TYPE_INFERRED_VECTOR:
+			return str_printf("%s[<*>]", type_to_error_string_with_path(type->array.base));
+		case TYPE_VECTOR:
+			return str_printf("%s[<%llu>]", type_to_error_string_with_path(type->array.base), (unsigned long long)type->array.len);
+		case TYPE_TYPEINFO:
+			return "typeinfo";
+		case TYPE_TYPEID:
+			return "typeid";
+		case TYPE_POINTER:
+			return str_printf("%s*", type_to_error_string_with_path(type->pointer));
+		case TYPE_OPTIONAL:
+			if (!type->optional) return "void?";
+			return str_printf("%s?", type_to_error_string_with_path(type->optional));
+		case TYPE_ARRAY:
+			return str_printf("%s[%llu]", type_to_error_string_with_path(type->array.base), (unsigned long long)type->array.len);
+		case TYPE_INFERRED_ARRAY:
+		case TYPE_FLEXIBLE_ARRAY:
+			return str_printf("%s[*]", type_to_error_string_with_path(type->array.base));
+		case TYPE_SLICE:
+			return str_printf("%s[]", type_to_error_string_with_path(type->array.base));
+	}
+	UNREACHABLE
+}
+
 
 bool type_is_matching_int(CanonicalType *type1, CanonicalType *type2)
 {

test/test_suite/cast/implicit_cast_same_name.c3

@@ -0,0 +1,15 @@
+module foo::a;
+struct Lexer { int a; }
+fn void foo(Lexer *lex) {}
+
+module foo::b;
+struct Lexer { int a; }
+fn void foo(Lexer *lex) {}
+
+module foo;
+
+fn void bar()
+{
+  a::Lexer l;
+  b::foo(&l); // #error: Implicitly casting 'foo::a::Lexer*' to 'foo::b::Lexer*' is not permitted, but you may do an explicit cast by placing '(foo::b::Lexer*)' before the expression
+}