bool safe_to_write(ast_t* ast, ast_t* type)
{
switch(ast_id(ast))
{
case TK_VAR:
case TK_LET:
case TK_VARREF:
case TK_DONTCARE:
return true;
case TK_FVARREF:
case TK_FLETREF:
case TK_EMBEDREF:
{
// If the ast is x.f, we need the type of x, which will be a nominal
// type or an arrow type, since we were able to lookup a field on it.
AST_GET_CHILDREN(ast, left, right);
ast_t* l_type = ast_type(left);
// Any viewpoint adapted type will not be safe to write to.
if(ast_id(l_type) != TK_NOMINAL)
return false;
token_id l_cap = cap_single(l_type);
// If the RHS is safe to write, we're done.
if(safe_field_write(l_cap, type))
return true;
// If the field type (without adaptation) is safe, then it's ok as
// well. So iso.tag = ref should be allowed.
ast_t* r_type = ast_type(right);
return safe_field_write(l_cap, r_type);
}
case TK_TUPLE:
{
// At this point, we know these will be the same length.
assert(ast_id(type) == TK_TUPLETYPE);
ast_t* child = ast_child(ast);
ast_t* type_child = ast_child(type);
while(child != NULL)
{
if(!safe_to_write(child, type_child))
return false;
child = ast_sibling(child);
type_child = ast_sibling(type_child);
}
assert(type_child == NULL);
return true;
}
case TK_SEQ:
{
// Occurs when there is a tuple on the left. Each child of the tuple will
// be a sequence, but only sequences with a single writeable child are
// valid. Other types won't appear here.
return safe_to_write(ast_child(ast), type);
}
default: {}
}
assert(0);
return false;
}
bool expr_assign(pass_opt_t* opt, ast_t* ast)
{
// Left and right are swapped in the AST to make sure we type check the
// right side before the left. Fetch them in the opposite order.
assert(ast != NULL);
AST_GET_CHILDREN(ast, right, left);
ast_t* l_type = ast_type(left);
if(!is_lvalue(&opt->check, left, is_result_needed(ast)))
{
ast_error(ast, "left side must be something that can be assigned to");
return false;
}
assert(l_type != NULL);
if(!coerce_literals(&right, l_type, opt))
return false;
ast_t* r_type = ast_type(right);
if(is_typecheck_error(r_type))
return false;
if(!infer_locals(left, r_type))
return false;
// Inferring locals may have changed the left type.
l_type = ast_type(left);
// Assignment is based on the alias of the right hand side.
ast_t* a_type = alias(r_type);
if(!is_subtype(a_type, l_type))
{
ast_error(ast, "right side must be a subtype of left side");
ast_error(a_type, "right side type: %s", ast_print_type(a_type));
ast_error(l_type, "left side type: %s", ast_print_type(l_type));
ast_free_unattached(a_type);
return false;
}
if((ast_id(left) == TK_TUPLE) && (ast_id(a_type) != TK_TUPLETYPE))
{
switch(ast_id(a_type))
{
case TK_UNIONTYPE:
ast_error(ast,
"can't destructure a union using assignment, use pattern matching "
"instead");
break;
case TK_ISECTTYPE:
ast_error(ast,
"can't destructure an intersection using assignment, use pattern "
"matching instead");
break;
default:
assert(0);
break;
}
ast_error(a_type, "right side type: %s", ast_print_type(a_type));
ast_free_unattached(a_type);
return false;
}
bool ok_safe = safe_to_write(left, a_type);
if(!ok_safe)
{
if(ast_id(left) == TK_FVARREF && ast_child(left) != NULL &&
ast_id(ast_child(left)) == TK_THIS)
{
// We are writing to a field in this
ast_t* fn = ast_nearest(left, TK_FUN);
if(fn != NULL)
{
ast_t* iso = ast_child(fn);
assert(iso != NULL);
token_id iso_id = ast_id(iso);
if(iso_id == TK_BOX || iso_id == TK_VAL || iso_id == TK_TAG)
{
ast_error(ast, "cannot write to a field in a %s function",
lexer_print(iso_id));
ast_free_unattached(a_type);
return false;
}
}
}
ast_error(ast, "not safe to write right side to left side");
ast_error(a_type, "right side type: %s", ast_print_type(a_type));
ast_free_unattached(a_type);
return false;
}
ast_free_unattached(a_type);
// If it's an embedded field, check for a constructor result.
if(ast_id(left) == TK_EMBEDREF)
{
if((ast_id(right) != TK_CALL) ||
(ast_id(ast_childidx(right, 2)) != TK_NEWREF))
{
ast_error(ast, "an embedded field must be assigned using a constructor");
return false;
}
}
ast_settype(ast, consume_type(l_type, TK_NONE));
ast_inheritflags(ast);
return true;
}
bool expr_assign(pass_opt_t* opt, ast_t* ast)
{
// Left and right are swapped in the AST to make sure we type check the
// right side before the left. Fetch them in the opposite order.
assert(ast != NULL);
AST_GET_CHILDREN(ast, right, left);
ast_t* l_type = ast_type(left);
if(l_type == NULL || !is_lvalue(opt, left, is_result_needed(ast)))
{
ast_error(opt->check.errors, ast,
"left side must be something that can be assigned to");
return false;
}
if(!coerce_literals(&right, l_type, opt))
return false;
ast_t* r_type = ast_type(right);
if(is_typecheck_error(r_type))
return false;
if(is_control_type(r_type))
{
ast_error(opt->check.errors, ast,
"the right hand side does not return a value");
return false;
}
if(!infer_locals(opt, left, r_type))
return false;
// Inferring locals may have changed the left type.
l_type = ast_type(left);
// Assignment is based on the alias of the right hand side.
ast_t* a_type = alias(r_type);
errorframe_t info = NULL;
if(!is_subtype(a_type, l_type, &info, opt))
{
errorframe_t frame = NULL;
ast_error_frame(&frame, ast, "right side must be a subtype of left side");
errorframe_append(&frame, &info);
errorframe_report(&frame, opt->check.errors);
ast_free_unattached(a_type);
return false;
}
if((ast_id(left) == TK_TUPLE) && (ast_id(a_type) != TK_TUPLETYPE))
{
switch(ast_id(a_type))
{
case TK_UNIONTYPE:
ast_error(opt->check.errors, ast,
"can't destructure a union using assignment, use pattern matching "
"instead");
break;
case TK_ISECTTYPE:
ast_error(opt->check.errors, ast,
"can't destructure an intersection using assignment, use pattern "
"matching instead");
break;
default:
assert(0);
break;
}
ast_free_unattached(a_type);
return false;
}
bool ok_safe = safe_to_write(left, a_type);
if(!ok_safe)
{
if(ast_id(left) == TK_FVARREF && ast_child(left) != NULL &&
ast_id(ast_child(left)) == TK_THIS)
{
// We are writing to a field in this
ast_t* fn = ast_nearest(left, TK_FUN);
if(fn != NULL)
{
ast_t* iso = ast_child(fn);
assert(iso != NULL);
token_id iso_id = ast_id(iso);
if(iso_id == TK_BOX || iso_id == TK_VAL || iso_id == TK_TAG)
{
ast_error(opt->check.errors, ast,
"cannot write to a field in a %s function. If you are trying to "
"change state in a function use fun ref",
lexer_print(iso_id));
ast_free_unattached(a_type);
return false;
}
}
}
ast_error(opt->check.errors, ast,
"not safe to write right side to left side");
ast_error_continue(opt->check.errors, a_type, "right side type: %s",
ast_print_type(a_type));
ast_free_unattached(a_type);
return false;
}
ast_free_unattached(a_type);
if(!check_embed_construction(opt, left, right))
return false;
ast_settype(ast, consume_type(l_type, TK_NONE));
return true;
}
