Bugfix #778: Flag for entry into for loop after range has been processed (#795)

* #778: Flag for entry into for loop after range has been processed

* Add regression test

* Added requested regression tests

* Changing style to `_tag`

For better or worse, I've been using `_tag` types instead of adding to the `start`/`end` names, so just staying consistent for now.

---------

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

Author: fknauf

regression-tests/pure2-for-loop-range-with-lambda.cpp2

@@ -0,0 +1,30 @@
+first: (forward f, forward _...) -> forward _ = f;
+
+main: (args) = {
+   ints: const std::array = (1, 2, 3, 4, 5);
+   // OK
+   for ints.first() do (i) {
+      std::cout << i;
+   }
+
+   // OK
+   for ints.first(1) do (i)  {
+      std::cout << i;
+   }
+
+   // Used to cause Error
+   for ints.first(:(x) x) do (i)   {
+      std::cout << i;
+   }
+
+   // OK
+   temp := ints.first(:(x) x);
+   for temp do (i) {
+      std::cout << i;
+   }
+
+   for :() args$;() do (i) _ = i;
+   for :(x) x;(args) do (j) _ = j;
+   for :(x) x;(args) next _ = :() args$;() do (k) _ = k;
+   for :(x) x;(args) next _ = :(x) x;(args) do (l) _ = l;
+}

regression-tests/test-results/pure2-for-loop-range-with-lambda.cpp

@@ -0,0 +1,56 @@
+
+#define CPP2_IMPORT_STD          Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-for-loop-range-with-lambda.cpp2"
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-for-loop-range-with-lambda.cpp2"
+[[nodiscard]] auto first(auto&& f, [[maybe_unused]] auto&& ...unnamed_param_2) -> auto&&;
+
+#line 3 "pure2-for-loop-range-with-lambda.cpp2"
+auto main(int const argc_, char** argv_) -> int;
+
+//=== Cpp2 function definitions =================================================
+
+#line 1 "pure2-for-loop-range-with-lambda.cpp2"
+[[nodiscard]] auto first(auto&& f, [[maybe_unused]] auto&& ...unnamed_param_2) -> auto&& { return CPP2_FORWARD(f);  }
+
+#line 3 "pure2-for-loop-range-with-lambda.cpp2"
+auto main(int const argc_, char** argv_) -> int{
+   auto const args = cpp2::make_args(argc_, argv_); 
+#line 4 "pure2-for-loop-range-with-lambda.cpp2"
+   std::array const ints {1, 2, 3, 4, 5}; 
+   // OK
+   for ( auto const& i : CPP2_UFCS(first)(ints) ) {
+      std::cout << i;
+   }
+
+   // OK
+   for (                 auto const& i : CPP2_UFCS(first)(ints, 1) ) {
+      std::cout << i;
+   }
+
+   // Used to cause Error
+   for (                      auto const& i : CPP2_UFCS(first)(ints, [](auto const& x) mutable -> auto { return x; }) ) {
+      std::cout << i;
+   }
+
+   // OK
+   auto temp {CPP2_UFCS(first)(std::move(ints), [](auto const& x) mutable -> auto { return x;  })}; 
+   for ( auto const& i : temp ) {
+      std::cout << i;
+   }
+
+   for ( auto const& i : [_0 = args]() mutable -> auto { return _0;  }() ) static_cast<void>(i); 
+   for ( auto const& j : [](auto const& x) mutable -> auto { return x;  }(args) ) static_cast<void>(j); 
+   for ( auto const& k : [](auto const& x) mutable -> auto { return x;  }(args) )  { do static_cast<void>(k);  while (false); static_cast<void>([_0 = args]() mutable -> auto { return _0;  }()); }
+   for ( auto const& l : [](auto const& x) mutable -> auto { return x;  }(args) )  { do static_cast<void>(l);  while (false); static_cast<void>([](auto const& x) mutable -> auto { return x;  }(args)); }
+}
+

regression-tests/test-results/pure2-for-loop-range-with-lambda.cpp2.output

@@ -0,0 +1,2 @@
+pure2-for-loop-range-with-lambda.cpp2... ok (all Cpp2, passes safety checks)
+

source/parse.h

@@ -4028,6 +4028,7 @@ auto primary_expression_node::visit(auto& v, int depth)
 
 
 struct next_expression_tag { };
+struct loop_body_tag { token const* identifier; };
 
 auto iteration_statement_node::visit(auto& v, int depth)
     -> void
@@ -4054,6 +4055,7 @@ auto iteration_statement_node::visit(auto& v, int depth)
     else {
         assert(range && parameter && body);
         range->visit(v, depth+1);
+        v.start(loop_body_tag{identifier}, depth);
         parameter->visit(v, depth+1);
         body->visit(v, depth+1);
     }

source/sema.h

@@ -1691,7 +1691,7 @@ class sema
         inside_returns_list = false;
     }
 
-    auto start(iteration_statement_node const& n, int) -> void
+    auto start(loop_body_tag const &n, int) -> void
     {
         if (*n.identifier == "for") {
             just_entered_for = true;