[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-check-pure-impure.cpp

@@ -0,0 +1,107 @@
+/*
+    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"
+#include "platform-utils.h"
+
+/*
+ *   This pipe checks for impure operations inside pure functions.
+ *   It happens after type inferring (after methods binding) since it operates fun_ref of calls.
+ */
+
+namespace tolk {
+
+GNU_ATTRIBUTE_NORETURN GNU_ATTRIBUTE_COLD
+static void fire_error_impure_operation_inside_pure_function(AnyV v) {
+  v->error("an impure operation in a pure function");
+}
+
+class CheckImpureOperationsInPureFunctionVisitor final : public ASTVisitorFunctionBody {
+  static void fire_if_global_var(AnyExprV v) {
+    if (auto v_ident = v->try_as<ast_identifier>()) {
+      if (v_ident->sym->try_as<GlobalVarData>()) {
+        fire_error_impure_operation_inside_pure_function(v);
+      }
+    }
+  }
+
+  void visit(V<ast_local_var> v) override {
+    if (v->marked_as_redef) {
+      fire_if_global_var(v->get_identifier());
+    }
+  }
+
+  void visit(V<ast_binary_operator> v) override {
+    if (v->is_set_assign() || v->is_assign()) {
+      fire_if_global_var(v->get_lhs());
+    }
+
+    parent::visit(v);
+  }
+
+  void visit(V<ast_function_call> v) override {
+    // most likely it's a global function, but also may be `some_var(args)` or even `getF()(args)`
+    if (!v->fun_maybe) {
+      // calling variables is always impure, no considerations about what's there at runtime
+      fire_error_impure_operation_inside_pure_function(v);
+    }
+
+    if (!v->fun_maybe->is_marked_as_pure()) {
+      fire_error_impure_operation_inside_pure_function(v);
+    }
+
+    parent::visit(v);
+  }
+
+  void visit(V<ast_dot_method_call> v) override {
+    if (!v->fun_ref->is_marked_as_pure()) {
+      fire_error_impure_operation_inside_pure_function(v);
+    }
+
+    parent::visit(v);
+  }
+
+  void visit(V<ast_argument> v) override {
+    if (v->passed_as_mutate) {
+      fire_if_global_var(v->get_expr());
+    }
+
+    parent::visit(v);
+  }
+
+  void visit(V<ast_throw_statement> v) override {
+    fire_error_impure_operation_inside_pure_function(v);
+  }
+
+  void visit(V<ast_assert_statement> v) override {
+    fire_error_impure_operation_inside_pure_function(v);
+  }
+
+public:
+  void start_visiting_function(V<ast_function_declaration> v_function) override {
+    if (v_function->marked_as_pure) {
+      parent::visit(v_function->get_body());
+    }
+  }
+};
+
+void pipeline_check_pure_impure_operations(const AllSrcFiles& all_src_files) {
+  visit_ast_of_all_functions<CheckImpureOperationsInPureFunctionVisitor>(all_src_files);
+}
+
+} // namespace tolk