prohibit semicolons in parameter list (#1100)

* prohibit semicolons in parameter list

* Formatting tweak: `{}` around branch bodies, 4-space indent

---------

Co-authored-by: Herb Sutter <[email protected]>

Author: sookach

source/parse.h

@@ -7732,7 +7732,7 @@ class parser
 
         //  Now the main declaration
         //
-        if (!(n->declaration = declaration(false, true, is_template))) {
+        if (!(n->declaration = declaration(false, true, is_template, {}, false))) {
             pos = start_pos;    // backtrack
             return {};
         }
@@ -8199,7 +8199,8 @@ class parser
         std::unique_ptr<unqualified_id_node> id                    = {},
         accessibility                        access                = {},
         bool                                 is_variadic           = false,
-        statement_node*                      my_stmt               = {}
+        statement_node*                      my_stmt               = {},
+        bool                                 semicolon_allowed     = true
     )
         -> std::unique_ptr<declaration_node>
     {
@@ -8505,11 +8506,18 @@ class parser
                 }
 
                 //  Then there may be a semicolon
-                //  If there is a semicolon, eat it
+                //  If there is a semicolon...
                 if (!done() && curr().type() == lexeme::Semicolon) {
-                    next();
+                    //  If it's allowed, eat it
+                    if (semicolon_allowed) {
+                        next();
+                    }
+                    // Otherwise, diagnose an error
+                    else {
+                        error("unexpected semicolon after declaration", {}, {}, {});
+                    }
                 }
-                // But if there isn't one and it was required, diagnose an error
+                //  Otherwise if there isn't one and it was required, diagnose an error
                 else if (semicolon_required) {
                     if (curr().type() == lexeme::LeftBrace) {
                         error("expected '=' before '{' - did you mean '= {' ?", true, {}, true);
@@ -8933,7 +8941,8 @@ class parser
         bool            semicolon_required    = true,
         bool            is_parameter          = false,
         bool            is_template_parameter = false,
-        statement_node* my_stmt               = {}
+        statement_node* my_stmt               = {},
+        bool            semicolon_allowed     = true
     )
         -> std::unique_ptr<declaration_node>
     {
@@ -9090,7 +9099,8 @@ class parser
                 std::move(id),
                 access,
                 is_variadic,
-                my_stmt
+                my_stmt,
+                semicolon_allowed
             );
             if (!n) {
                 pos = start_pos;    // backtrack