fix initializing undefined and crash when casting to invalid type

closes #408

src/analyze.cpp

@@ -3704,6 +3704,9 @@ void init_const_undefined(CodeGen *g, ConstExprValue *const_val) {
         const_val->data.x_array.special = ConstArraySpecialUndef;
     } else if (wanted_type->id == TypeTableEntryIdStruct) {
         ensure_complete_type(g, wanted_type);
+        if (type_is_invalid(wanted_type)) {
+            return;
+        }
 
         const_val->special = ConstValSpecialStatic;
         size_t field_count = wanted_type->data.structure.src_field_count;

src/ir.cpp

@@ -6945,6 +6945,9 @@ IrInstruction *ir_eval_const_value(CodeGen *codegen, Scope *scope, AstNode *node
         FnTableEntry *fn_entry, Buf *c_import_buf, AstNode *source_node, Buf *exec_name,
         IrExecutable *parent_exec)
 {
+    if (expected_type != nullptr && type_is_invalid(expected_type))
+        return codegen->invalid_instruction;
+
     IrExecutable ir_executable = {0};
     ir_executable.source_node = source_node;
     ir_executable.parent_exec = parent_exec;
@@ -14112,6 +14115,7 @@ TypeTableEntry *ir_analyze(CodeGen *codegen, IrExecutable *old_exec, IrExecutabl
         TypeTableEntry *expected_type, AstNode *expected_type_source_node)
 {
     assert(!old_exec->invalid);
+    assert(expected_type == nullptr || !type_is_invalid(expected_type));
 
     IrAnalyze ir_analyze_data = {};
     IrAnalyze *ira = &ir_analyze_data;

test/compile_errors.zig

@@ -1918,4 +1918,17 @@ pub fn addCases(cases: &tests.CompileErrorContext) {
         ".tmp_source.zig:1:13: error: aoeu",
         ".tmp_source.zig:3:19: note: referenced here",
         ".tmp_source.zig:7:12: note: referenced here");
+
+    cases.add("instantiating an undefined value for an invalid struct that contains itself",
+        \\const Foo = struct {
+        \\    x: Foo,
+        \\};
+        \\
+        \\var foo: Foo = undefined;
+        \\
+        \\export fn entry() -> usize {
+        \\    return @sizeOf(@typeOf(foo.x));
+        \\}
+    ,
+        ".tmp_source.zig:1:13: error: struct 'Foo' contains itself");
 }