[Tolk] AST-based semantic analysis, get rid of Expr

This is a huge refactoring focusing on untangling compiler internals
(previously forked from FunC).
The goal is to convert AST directly to Op (a kind of IR representation),
doing all code analysis at AST level.

Noteable changes:
- AST-based semantic kernel includes: registering global symbols,
  scope handling and resolving local/global identifiers,
  lvalue/rvalue calc and check, implicit return detection,
  mutability analysis, pure/impure validity checks,
  simple constant folding
- values of `const` variables are calculated NOT based on CodeBlob,
  but via a newly-introduced AST-based constant evaluator
- AST vertices are now inherited from expression/statement/other;
  expression vertices have common properties (TypeExpr, lvalue/rvalue)
- symbol table is rewritten completely, SymDef/SymVal no longer exist,
  lexer now doesn't need to register identifiers
- AST vertices have references to symbols, filled at different
  stages of pipeline
- the remaining "FunC legacy part" is almost unchanged besides Expr
  which was fully dropped; AST is converted to Ops (IR) directly

tolk/pipe-calc-rvalue-lvalue.cpp

@@ -0,0 +1,192 @@
+/*
+    This file is part of TON Blockchain source code.
+
+    TON Blockchain is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation; either version 2
+    of the License, or (at your option) any later version.
+
+    TON Blockchain is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with TON Blockchain.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#include "tolk.h"
+#include "ast.h"
+#include "ast-visitor.h"
+
+/*
+ *   This pipe assigns lvalue/rvalue flags for AST expressions.
+ *   It happens after identifiers have been resolved, but before type inferring (before methods binding).
+ *
+ *   Example: `a = b`, `a` is lvalue, `b` is rvalue.
+ *   Example: `a + b`, both are rvalue.
+ *
+ *   Note, that this pass only assigns, not checks. So, for `f() = 4`, expr `f()` is lvalue.
+ * Checking (firing this as incorrect later) is performed after type inferring, see pipe-check-rvalue-lvalue.
+ */
+
+namespace tolk {
+
+enum class MarkingState {
+  None,
+  LValue,
+  RValue,
+  LValueAndRValue
+};
+
+class CalculateRvalueLvalueVisitor final : public ASTVisitorFunctionBody {
+  MarkingState cur_state = MarkingState::None;
+
+  MarkingState enter_state(MarkingState activated) {
+    MarkingState saved = cur_state;
+    cur_state = activated;
+    return saved;
+  }
+
+  void restore_state(MarkingState saved) {
+    cur_state = saved;
+  }
+
+  void mark_vertex_cur_or_rvalue(AnyExprV v) const {
+    if (cur_state == MarkingState::LValue || cur_state == MarkingState::LValueAndRValue) {
+      v->mutate()->assign_lvalue_true();
+    }
+    if (cur_state == MarkingState::RValue || cur_state == MarkingState::LValueAndRValue || cur_state == MarkingState::None) {
+      v->mutate()->assign_rvalue_true();
+    }
+  }
+
+  void visit(V<ast_empty_expression> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+  
+  void visit(V<ast_parenthesized_expression> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    parent::visit(v);
+  }
+
+  void visit(V<ast_tensor> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    parent::visit(v);
+  }
+  
+  void visit(V<ast_tensor_square> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    parent::visit(v);
+  }
+
+  void visit(V<ast_identifier> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_int_const> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_string_const> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_bool_const> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_null_keyword> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_self_keyword> v) override {
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_argument> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(v->passed_as_mutate ? MarkingState::LValueAndRValue : MarkingState::RValue);
+    parent::visit(v);
+    restore_state(saved);
+  }
+
+  void visit(V<ast_argument_list> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    parent::visit(v);
+  }
+
+  void visit(V<ast_function_call> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(MarkingState::RValue);
+    parent::visit(v);
+    restore_state(saved);
+  }
+
+  void visit(V<ast_dot_method_call> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(MarkingState::RValue);
+    parent::visit(v->get_obj());
+    enter_state(MarkingState::RValue);
+    parent::visit(v->get_arg_list());
+    restore_state(saved);
+  }
+
+  void visit(V<ast_underscore> v) override {
+    // underscore is a placeholder to ignore left side of assignment: `(a, _) = get2params()`
+    // so, if current state is "lvalue", `_` will be marked as lvalue, and ok
+    // but if used incorrectly, like `f(_)` or just `_;`, it will be marked rvalue
+    // and will fire an error later, in pipe lvalue/rvalue check
+    mark_vertex_cur_or_rvalue(v);
+  }
+
+  void visit(V<ast_unary_operator> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(MarkingState::RValue);
+    parent::visit(v);
+    restore_state(saved);
+  }
+
+  void visit(V<ast_binary_operator> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(v->is_set_assign() ? MarkingState::LValueAndRValue : v->is_assign() ? MarkingState::LValue : MarkingState::RValue);
+    parent::visit(v->get_lhs());
+    enter_state(MarkingState::RValue);
+    parent::visit(v->get_rhs());
+    restore_state(saved);
+  }
+
+  void visit(V<ast_ternary_operator> v) override {
+    mark_vertex_cur_or_rvalue(v);
+    MarkingState saved = enter_state(MarkingState::RValue);
+    parent::visit(v);  // both cond, when_true and when_false are rvalue, `(cond ? a : b) = 5` prohibited
+    restore_state(saved);
+  }
+
+  void visit(V<ast_local_vars_declaration> v) override {
+    MarkingState saved = enter_state(MarkingState::LValue);
+    parent::visit(v->get_lhs());
+    enter_state(MarkingState::RValue);
+    parent::visit(v->get_assigned_val());
+    restore_state(saved);
+  }
+
+  void visit(V<ast_local_var> v) override {
+    tolk_assert(cur_state == MarkingState::LValue);
+    mark_vertex_cur_or_rvalue(v);
+    parent::visit(v);
+  }
+
+  void visit(V<ast_try_catch_statement> v) override {
+    parent::visit(v->get_try_body());
+    MarkingState saved = enter_state(MarkingState::LValue);
+    parent::visit(v->get_catch_expr());
+    restore_state(saved);
+    parent::visit(v->get_catch_body());
+  }
+};
+
+void pipeline_calculate_rvalue_lvalue(const AllSrcFiles& all_src_files) {
+  visit_ast_of_all_functions<CalculateRvalueLvalueVisitor>(all_src_files);
+}
+
+} // namespace tolk