Diagnose use of variable in its own initializer, closes #1028

Examples, now diagnosed:

    x: int = x;

    x: int = f(x);

NOT diagnosed:

    x := :(x) f(x);

Author: hsutter

Diff for: source/parse.h

@@ -2696,8 +2696,8 @@ struct declaration_node
     bool member_function_generation = true;
 
     //  Cache some context
-    bool is_template_parameter = false;
-    bool is_parameter          = false;
+    bool is_a_template_parameter = false;
+    bool is_a_parameter          = false;
 
     //  Constructor
     //
@@ -2707,6 +2707,19 @@ struct declaration_node
 
     //  API
     //
+
+    auto is_template_parameter() const
+        -> bool
+    {
+        return is_a_template_parameter;
+    }
+
+    auto is_parameter() const
+        -> bool
+    {
+        return is_a_parameter;
+    }
+
     auto type_member_mark_for_removal()
         -> bool
     {
@@ -5115,7 +5128,7 @@ auto pretty_print_visualize(declaration_node const& n, int indent, bool include_
             initializer.pop_back();
         }
     }
-    else if (!n.is_parameter) {
+    else if (!n.is_parameter()) {
         initializer = ";";
     }
 
@@ -5128,7 +5141,7 @@ auto pretty_print_visualize(declaration_node const& n, int indent, bool include_
     if (
         !n.parent_is_function()
         && !n.parent_is_object()
-        && !n.is_parameter
+        && !n.is_parameter()
         )
     {
         static declaration_node const* last_parent_type = {};
@@ -5144,7 +5157,7 @@ auto pretty_print_visualize(declaration_node const& n, int indent, bool include_
             ret += "\n";
         }
     }
-    if (!n.is_parameter && n.name()) {
+    if (!n.is_parameter() && n.name()) {
         ret += std::string{"\n"} + pre(indent);
     }
 
@@ -5159,7 +5172,7 @@ auto pretty_print_visualize(declaration_node const& n, int indent, bool include_
         ret += pretty_print_visualize(*n.identifier, indent);
     }
 
-    if (n.is_parameter && (n.has_name("this") || n.has_name("that"))) {
+    if (n.is_parameter() && (n.has_name("this") || n.has_name("that"))) {
         return ret;
     }
 
@@ -5758,7 +5771,7 @@ class parser
 
     //G postfix-expression:
     //G     primary-expression
-    //G     postfix-expression postfix-operator     [Note: without whitespace before the operator]
+    //G     postfix-expression postfix-operator     // Note: without whitespace before the operator
     //G     postfix-expression '[' expression-list? ','? ']'
     //G     postfix-expression '(' expression-list? ','? ')'
     //G     postfix-expression '.' id-expression
@@ -9074,8 +9087,8 @@ class parser
         }
 
         //  Cache some context
-        n->is_template_parameter = is_template_parameter;
-        n->is_parameter          = is_parameter;
+        n->is_a_template_parameter = is_template_parameter;
+        n->is_a_parameter          = is_parameter;
 
         return n;
     }

Diff for: source/sema.h

@@ -88,6 +88,7 @@ struct identifier_sym {
     enum kind { use, using_declaration, deactivation } kind_ = use;
     bool standalone_assignment_to = false;
     bool is_captured = false;
+    bool is_after_dot = false;
     bool safe_to_move = true;
     int safe_to_move_context = 0;
     token const* identifier = {};
@@ -97,10 +98,12 @@ struct identifier_sym {
         token const* id,
         kind         k = use,
         bool         mv = true,
-        int          mvc = 0
+        int          mvc = 0,
+        bool         after_dot = false
     )
         : kind_{k}
         , standalone_assignment_to{a}
+        , is_after_dot{after_dot}
         , safe_to_move{mv}
         , safe_to_move_context{mvc}
         , identifier{id}
@@ -731,7 +734,8 @@ class sema
                 find_definite_last_uses(
                     decl->identifier,
                     sympos,
-                    decl->parameter ? std::optional{decl->parameter->pass} : std::optional<passing_style>{}
+                    decl->parameter ? std::optional{decl->parameter->pass} : std::optional<passing_style>{},
+                    decl->parameter
                 );
             }
         }
@@ -746,7 +750,8 @@ class sema
     auto find_definite_last_uses(
         token const*                 id,
         int                          pos,
-        std::optional<passing_style> pass
+        std::optional<passing_style> pass,
+        bool                         is_parameter
     ) const
         -> void
     {
@@ -883,12 +888,47 @@ class sema
         };
 
         //  Scan forward to the end of this scope
+        auto found_end_of_our_initialization = false;
         for (auto start_depth = symbols[pos].depth;
             i < std::ssize(symbols)
             && symbols[i].depth >= start_depth;
             ++i
             )
         {
+            //  While we're here, if this is a non-parameter local, check for
+            //  any uses before the end of the initializer
+            if (
+                !is_parameter
+                && !found_end_of_our_initialization
+                )
+            {
+                if (symbols[i].depth == start_depth)
+                {
+                    if (auto decl = std::get_if<symbol::active::declaration>(&symbols[i].sym);
+                        decl
+                        && decl->declaration->is_object()
+                        && decl->declaration->has_name(*id)
+                        && !decl->start
+                        )
+                    {
+                        found_end_of_our_initialization = true;
+                    }
+                }
+
+                if (auto sym = std::get_if<symbol::active::identifier>(&symbols[i].sym);
+                    sym
+                    && !sym->is_after_dot
+                    && is_a_use(sym)
+                    )
+                {
+                    assert(sym->identifier);
+                    errors.emplace_back(
+                        sym->identifier->position(),
+                        "local variable " + sym->identifier->to_string()
+                            + " cannot be used in its own initializer");
+                }
+            }
+
             if (
                 skip_function_expression()
                 || skip_hidden_name(true)
@@ -1565,9 +1605,9 @@ class sema
         if (n.identifier && *n.identifier->identifier == "this")
         {
             if (
-                n.is_template_parameter
+                n.is_template_parameter()
                 || (
-                    !n.is_parameter
+                    !n.is_parameter()
                     && !n.parent_is_type()
                     )
                 )
@@ -2430,12 +2470,19 @@ class sema
                 //  or it's a 'copy' parameter (but to be a use it must be after
                 //  the declaration, not the token in the decl's name itself)
                 //  including an implicit 'this' access of a member name
-                auto push_use = [&](token const* u) {
-                    this->push_use( identifier_sym( false, u, {}, !inside_next_expression, safe_to_move_context ) );
+                auto push_use = [&](token const* u, bool is_dot_access = false) {
+                    this->push_use( identifier_sym(
+                        false,
+                        u,
+                        {},
+                        !inside_next_expression,
+                        safe_to_move_context,
+                        is_dot_access
+                    ) );
                 };
                 if (accessed_member_for_ufcs) {
                     if (t == "(") {
-                        push_use(accessed_member_for_ufcs);
+                        push_use(accessed_member_for_ufcs, true);
                     }
                     accessed_member_for_ufcs = nullptr;
                 }