py: Improve handling of memory error in parser.

Parser shouldn't raise exceptions, so needs to check when memory
allocation fails.  This patch does that for the initial set up of the
parser state.

Also, we now put the parser object on the stack.  It's small enough to
go there instead of on the heap.

This partially addresses issue #558.

1 files changed, 52 insertions, 47 deletions

diff --git a/py/parse.c b/py/parse.c
index 0ec336cd1a..f5efd7a4f4 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -344,21 +344,26 @@ STATIC void push_result_rule(parser_t *parser, int src_line, const rule_t *rule,
 
 mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_parse_error_kind_t *parse_error_kind_out) {
 
-    // allocate memory for the parser and its stacks
+    // initialise parser and allocate memory for its stacks
 
-    parser_t *parser = m_new_obj(parser_t);
+    parser_t parser;
 
-    parser->had_memory_error = false;
+    parser.had_memory_error = false;
 
-    parser->rule_stack_alloc = MP_ALLOC_PARSE_RULE_INIT;
-    parser->rule_stack_top = 0;
-    parser->rule_stack = m_new(rule_stack_t, parser->rule_stack_alloc);
+    parser.rule_stack_alloc = MP_ALLOC_PARSE_RULE_INIT;
+    parser.rule_stack_top = 0;
+    parser.rule_stack = m_new_maybe(rule_stack_t, parser.rule_stack_alloc);
 
-    parser->result_stack_alloc = MP_ALLOC_PARSE_RESULT_INIT;
-    parser->result_stack_top = 0;
-    parser->result_stack = m_new(mp_parse_node_t, parser->result_stack_alloc);
+    parser.result_stack_alloc = MP_ALLOC_PARSE_RESULT_INIT;
+    parser.result_stack_top = 0;
+    parser.result_stack = m_new_maybe(mp_parse_node_t, parser.result_stack_alloc);
 
-    parser->lexer = lex;
+    parser.lexer = lex;
+
+    // check if we could allocate the stacks
+    if (parser.rule_stack == NULL || parser.result_stack == NULL) {
+        goto memory_error;
+    }
 
     // work out the top-level rule to use, and push it on the stack
     int top_level_rule;
@@ -367,7 +372,7 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
         case MP_PARSE_EVAL_INPUT: top_level_rule = RULE_eval_input; break;
         default: top_level_rule = RULE_file_input;
     }
-    push_rule(parser, mp_lexer_cur(lex)->src_line, rules[top_level_rule], 0);
+    push_rule(&parser, mp_lexer_cur(lex)->src_line, rules[top_level_rule], 0);
 
     // parse!
 
@@ -381,17 +386,17 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
 
     for (;;) {
         next_rule:
-        if (parser->rule_stack_top == 0 || parser->had_memory_error) {
+        if (parser.rule_stack_top == 0 || parser.had_memory_error) {
             break;
         }
 
-        pop_rule(parser, &rule, &i, &rule_src_line);
+        pop_rule(&parser, &rule, &i, &rule_src_line);
         n = rule->act & RULE_ACT_ARG_MASK;
 
         /*
         // debugging
-        printf("depth=%d ", parser->rule_stack_top);
-        for (int j = 0; j < parser->rule_stack_top; ++j) {
+        printf("depth=%d ", parser.rule_stack_top);
+        for (int j = 0; j < parser.rule_stack_top; ++j) {
             printf(" ");
         }
         printf("%s n=%d i=%d bt=%d\n", rule->rule_name, n, i, backtrack);
@@ -408,14 +413,14 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                     switch (rule->arg[i] & RULE_ARG_KIND_MASK) {
                         case RULE_ARG_TOK:
                             if (mp_lexer_is_kind(lex, rule->arg[i] & RULE_ARG_ARG_MASK)) {
-                                push_result_token(parser, lex);
+                                push_result_token(&parser, lex);
                                 mp_lexer_to_next(lex);
                                 goto next_rule;
                             }
                             break;
                         case RULE_ARG_RULE:
-                            push_rule(parser, rule_src_line, rule, i + 1); // save this or-rule
-                            push_rule_from_arg(parser, rule->arg[i]); // push child of or-rule
+                            push_rule(&parser, rule_src_line, rule, i + 1); // save this or-rule
+                            push_rule_from_arg(&parser, rule->arg[i]); // push child of or-rule
                             goto next_rule;
                         default:
                             assert(0);
@@ -423,14 +428,14 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                 }
                 if ((rule->arg[i] & RULE_ARG_KIND_MASK) == RULE_ARG_TOK) {
                     if (mp_lexer_is_kind(lex, rule->arg[i] & RULE_ARG_ARG_MASK)) {
-                        push_result_token(parser, lex);
+                        push_result_token(&parser, lex);
                         mp_lexer_to_next(lex);
                     } else {
                         backtrack = true;
                         goto next_rule;
                     }
                 } else {
-                    push_rule_from_arg(parser, rule->arg[i]);
+                    push_rule_from_arg(&parser, rule->arg[i]);
                 }
                 break;
 
@@ -441,7 +446,7 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                     assert(i > 0);
                     if ((rule->arg[i - 1] & RULE_ARG_KIND_MASK) == RULE_ARG_OPT_RULE) {
                         // an optional rule that failed, so continue with next arg
-                        push_result_node(parser, MP_PARSE_NODE_NULL);
+                        push_result_node(&parser, MP_PARSE_NODE_NULL);
                         backtrack = false;
                     } else {
                         // a mandatory rule that failed, so propagate backtrack
@@ -463,7 +468,7 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                             if (mp_lexer_is_kind(lex, tok_kind)) {
                                 // matched token
                                 if (tok_kind == MP_TOKEN_NAME) {
-                                    push_result_token(parser, lex);
+                                    push_result_token(&parser, lex);
                                 }
                                 mp_lexer_to_next(lex);
                             } else {
@@ -480,8 +485,8 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                             break;
                         case RULE_ARG_RULE:
                         case RULE_ARG_OPT_RULE:
-                            push_rule(parser, rule_src_line, rule, i + 1); // save this and-rule
-                            push_rule_from_arg(parser, rule->arg[i]); // push child of and-rule
+                            push_rule(&parser, rule_src_line, rule, i + 1); // save this and-rule
+                            push_rule_from_arg(&parser, rule->arg[i]); // push child of and-rule
                             goto next_rule;
                         default:
                             assert(0);
@@ -514,12 +519,12 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
 #if 0 && !MICROPY_ENABLE_DOC_STRING
                 // this code discards lonely statement, such as doc strings
                 // problem is that doc strings have already been interned, so this doesn't really help reduce RAM usage
-                if (input_kind != MP_PARSE_SINGLE_INPUT && rule->rule_id == RULE_expr_stmt && peek_result(parser, 0) == MP_PARSE_NODE_NULL) {
-                    mp_parse_node_t p = peek_result(parser, 1);
+                if (input_kind != MP_PARSE_SINGLE_INPUT && rule->rule_id == RULE_expr_stmt && peek_result(&parser, 0) == MP_PARSE_NODE_NULL) {
+                    mp_parse_node_t p = peek_result(&parser, 1);
                     if (MP_PARSE_NODE_IS_LEAF(p) && !MP_PARSE_NODE_IS_ID(p)) {
                         pop_result(parser);
                         pop_result(parser);
-                        push_result_rule(parser, rule_src_line, rules[RULE_pass_stmt], 0);
+                        push_result_rule(&parser, rule_src_line, rules[RULE_pass_stmt], 0);
                         break;
                     }
                 }
@@ -540,35 +545,35 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                 // always emit these rules, and add an extra blank node at the end (to be used by the compiler to store data)
                 if (ADD_BLANK_NODE(rule->rule_id)) {
                     emit_rule = true;
-                    push_result_node(parser, MP_PARSE_NODE_NULL);
+                    push_result_node(&parser, MP_PARSE_NODE_NULL);
                     i += 1;
                 }
 
                 int num_not_nil = 0;
                 for (int x = 0; x < i; ++x) {
-                    if (peek_result(parser, x) != MP_PARSE_NODE_NULL) {
+                    if (peek_result(&parser, x) != MP_PARSE_NODE_NULL) {
                         num_not_nil += 1;
                     }
                 }
                 //printf("done and %s n=%d i=%d notnil=%d\n", rule->rule_name, n, i, num_not_nil);
                 if (emit_rule) {
-                    push_result_rule(parser, rule_src_line, rule, i);
+                    push_result_rule(&parser, rule_src_line, rule, i);
                 } else if (num_not_nil == 0) {
-                    push_result_rule(parser, rule_src_line, rule, i); // needed for, eg, atom_paren, testlist_comp_3b
+                    push_result_rule(&parser, rule_src_line, rule, i); // needed for, eg, atom_paren, testlist_comp_3b
                     //result_stack_show(parser);
                     //assert(0);
                 } else if (num_not_nil == 1) {
                     // single result, leave it on stack
                     mp_parse_node_t pn = MP_PARSE_NODE_NULL;
                     for (int x = 0; x < i; ++x) {
-                        mp_parse_node_t pn2 = pop_result(parser);
+                        mp_parse_node_t pn2 = pop_result(&parser);
                         if (pn2 != MP_PARSE_NODE_NULL) {
                             pn = pn2;
                         }
                     }
-                    push_result_node(parser, pn);
+                    push_result_node(&parser, pn);
                 } else {
-                    push_result_rule(parser, rule_src_line, rule, i);
+                    push_result_rule(&parser, rule_src_line, rule, i);
                 }
                 break;
 
@@ -615,7 +620,7 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                                     if (i & 1 & n) {
                                         // separators which are tokens are not pushed to result stack
                                     } else {
-                                        push_result_token(parser, lex);
+                                        push_result_token(&parser, lex);
                                     }
                                     mp_lexer_to_next(lex);
                                     // got element of list, so continue parsing list
@@ -628,8 +633,8 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                                 }
                                 break;
                             case RULE_ARG_RULE:
-                                push_rule(parser, rule_src_line, rule, i + 1); // save this list-rule
-                                push_rule_from_arg(parser, arg); // push child of list-rule
+                                push_rule(&parser, rule_src_line, rule, i + 1); // save this list-rule
+                                push_rule_from_arg(&parser, arg); // push child of list-rule
                                 goto next_rule;
                             default:
                                 assert(0);
@@ -649,13 +654,13 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
                     // list matched single item
                     if (had_trailing_sep) {
                         // if there was a trailing separator, make a list of a single item
-                        push_result_rule(parser, rule_src_line, rule, i);
+                        push_result_rule(&parser, rule_src_line, rule, i);
                     } else {
                         // just leave single item on stack (ie don't wrap in a list)
                     }
                 } else {
                     //printf("done list %s %d %d\n", rule->rule_name, n, i);
-                    push_result_rule(parser, rule_src_line, rule, i);
+                    push_result_rule(&parser, rule_src_line, rule, i);
                 }
                 break;
 
@@ -667,7 +672,8 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
     mp_parse_node_t result;
 
     // check if we had a memory error
-    if (parser->had_memory_error) {
+    if (parser.had_memory_error) {
+memory_error:
         *parse_error_kind_out = MP_PARSE_ERROR_MEMORY;
         result = MP_PARSE_NODE_NULL;
         goto finished;
@@ -681,19 +687,18 @@ mp_parse_node_t mp_parse(mp_lexer_t *lex, mp_parse_input_kind_t input_kind, mp_p
 
     //printf("--------------\n");
     //result_stack_show(parser);
-    //printf("rule stack alloc: %d\n", parser->rule_stack_alloc);
-    //printf("result stack alloc: %d\n", parser->result_stack_alloc);
+    //printf("rule stack alloc: %d\n", parser.rule_stack_alloc);
+    //printf("result stack alloc: %d\n", parser.result_stack_alloc);
     //printf("number of parse nodes allocated: %d\n", num_parse_nodes_allocated);
 
     // get the root parse node that we created
-    assert(parser->result_stack_top == 1);
-    result = parser->result_stack[0];
+    assert(parser.result_stack_top == 1);
+    result = parser.result_stack[0];
 
 finished:
     // free the memory that we don't need anymore
-    m_del(rule_stack_t, parser->rule_stack, parser->rule_stack_alloc);
-    m_del(mp_parse_node_t, parser->result_stack, parser->result_stack_alloc);
-    m_del_obj(parser_t, parser);
+    m_del(rule_stack_t, parser.rule_stack, parser.rule_stack_alloc);
+    m_del(mp_parse_node_t, parser.result_stack, parser.result_stack_alloc);
 
     // return the result
     return result;