Re-enable move from last use in initializers, closes #749

hsutter · hsutter · commit 8a9346033ad5 · 2023-11-14T10:49:15.000-10:00
I was trying out suppressing move-from-last-use if the last use was in an initializer, because of examples like `view: std::span = local_variable;` when that was the last use of `local_variable`, which is an error for an rvalue. But that also suppresses a righteous move in examples like `result := local_variable;`. So I now agree those should be treated as rvalues too, and if that causes an error for an rvalue because there is no further us of that variable in scope, then the programmer must write an explicit discard of the variable.
diff --git a/regression-tests/mixed-function-expression-and-std-for-each.cpp2 b/regression-tests/mixed-function-expression-and-std-for-each.cpp2
@@ -7,24 +7,21 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2022");
-    view: std::span = vec;
 
     //  Passing a function expression
-    std::for_each(
-        view.begin(),
-        view.end(),
-        :(inout x) = x += "-ish";
+    std::ranges::for_each(
+        vec,
+        :(inout x) = x += "-ish"
     );
 
     //  Initializing from a function expression
     callback := :(inout x) = x += " maybe";
-    std::for_each(
-        view.begin(),
-        view.end(),
+    std::ranges::for_each(
+        vec,
         callback
     );
 
-    for view do (str) {
+    for vec do (str) {
         std::cout << str << "\n";
     }
 }
diff --git a/regression-tests/mixed-function-expression-and-std-ranges-for-each-with-capture.cpp2 b/regression-tests/mixed-function-expression-and-std-ranges-for-each-with-capture.cpp2
@@ -8,15 +8,14 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2022");
-    view: std::span = vec;
 
     y := "\n";
     std::ranges::for_each
-        ( view, :(x) = std::cout << x << y$ );
+        ( vec, :(x) = std::cout << x << y$ );
 
     callback := :(inout x) = x += "-ish";
-    std::ranges::for_each( view, callback );
+    std::ranges::for_each( vec, callback );
 
-    for view do (str)
+    for vec do (str)
         std::cout << str << "\n";
 }
diff --git a/regression-tests/mixed-function-expression-and-std-ranges-for-each.cpp2 b/regression-tests/mixed-function-expression-and-std-ranges-for-each.cpp2
@@ -8,14 +8,13 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2022");
-    view: std::span = vec;
 
     std::ranges::for_each
-        ( view, :(x) = std::cout << x << "\n" );
+        ( vec, :(x) = std::cout << x << "\n" );
 
     callback := :(inout x) = x += "-ish";
-    std::ranges::for_each( view, callback );
+    std::ranges::for_each( vec, callback );
 
-    for view do (str)
+    for vec do (str)
         std::cout << str << "\n";
 }
diff --git a/regression-tests/mixed-function-expression-with-pointer-capture.cpp2 b/regression-tests/mixed-function-expression-with-pointer-capture.cpp2
@@ -8,16 +8,15 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2023");
-    view: std::span = vec;
 
     y: std::string = "\n";
-    std::ranges::for_each( view, :(x) =
-        std::cout << y&$*.c_str() << x << y&$*;
+    std::ranges::for_each( vec, :(x) =
+        std::cout << y&$*.c_str() << x << y&$*
     );
 
     callback := :(inout x) = x += "-ish";
-    std::ranges::for_each( view, callback );
+    std::ranges::for_each( vec, callback );
 
-    for view do (str)
+    for vec do (str)
         std::cout << str << "\n";
 }
diff --git a/regression-tests/mixed-function-expression-with-repeated-capture.cpp2 b/regression-tests/mixed-function-expression-with-repeated-capture.cpp2
@@ -8,15 +8,14 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2022");
-    view: std::span = vec;
 
     y := "\n";
     std::ranges::for_each
-        ( view, :(x) = std::cout << y$ << x << y$ );
+        ( vec, :(x) = std::cout << y$ << x << y$ );
 
     callback := :(inout x) = x += "-ish";
-    std::ranges::for_each( view, callback );
+    std::ranges::for_each( vec, callback );
 
-    for view do (str)
+    for vec do (str)
         std::cout << str << "\n";
 }
diff --git a/regression-tests/pure2-bounds-safety-span.cpp2 b/regression-tests/pure2-bounds-safety-span.cpp2
@@ -4,6 +4,7 @@ main: () -> int
     words: std::vector<std::string> = ( "decorated", "hello", "world" );
 
     s: std::span<std::string> = words;
+    _ = words;
 
     i := 0;
     while i < s.ssize() next i++ {
diff --git a/regression-tests/pure2-intro-example-hello-2022.cpp2 b/regression-tests/pure2-intro-example-hello-2022.cpp2
@@ -1,9 +1,8 @@
 main: () -> int = {
     vec: std::vector<std::string>
             = ("hello", "2022");
-    view: std::span = vec;
 
-    for view do (inout str) {
+    for vec do (inout str) {
         len := decorate(str);
         print_it(str, len);
     }
diff --git a/regression-tests/test-results/mixed-function-expression-and-std-for-each.cpp b/regression-tests/test-results/mixed-function-expression-and-std-for-each.cpp
@@ -26,24 +26,21 @@
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2022"}; 
-    std::span view {vec}; 
 
     //  Passing a function expression
-    std::for_each(
-        CPP2_UFCS_0(begin, view), 
-        CPP2_UFCS_0(end, view), 
+    std::ranges::for_each(
+        vec, 
         [](auto& x) -> void { x += "-ish";  }
     );
 
     //  Initializing from a function expression
     auto callback {[](auto& x) -> void { x += " maybe";  }}; 
-    std::for_each(
-        CPP2_UFCS_0(begin, view), 
-        CPP2_UFCS_0(end, view), 
+    std::ranges::for_each(
+        vec, 
         std::move(callback)
     );
 
-    for ( auto const& str : view ) {
+    for ( auto const& str : vec ) {
         std::cout << str << "\n";
     }
 }
diff --git a/regression-tests/test-results/mixed-function-expression-and-std-ranges-for-each-with-capture.cpp b/regression-tests/test-results/mixed-function-expression-and-std-ranges-for-each-with-capture.cpp
@@ -27,16 +27,15 @@
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2022"}; 
-    std::span view {vec}; 
 
     auto y {"\n"}; 
     std::ranges::for_each
-        (view, [_0 = std::move(y)](auto const& x) -> void { std::cout << x << _0;  });
+        (vec, [_0 = std::move(y)](auto const& x) -> void { std::cout << x << _0;  });
 
     auto callback {[](auto& x) -> void { x += "-ish";  }}; 
-    std::ranges::for_each(view, std::move(callback));
+    std::ranges::for_each(vec, std::move(callback));
 
-    for ( auto const& str : view ) 
+    for ( auto const& str : vec ) 
         std::cout << str << "\n";
 }
 
diff --git a/regression-tests/test-results/mixed-function-expression-and-std-ranges-for-each.cpp b/regression-tests/test-results/mixed-function-expression-and-std-ranges-for-each.cpp
@@ -27,15 +27,14 @@
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2022"}; 
-    std::span view {vec}; 
 
     std::ranges::for_each
-        (view, [](auto const& x) -> void { std::cout << x << "\n";  });
+        (vec, [](auto const& x) -> void { std::cout << x << "\n";  });
 
     auto callback {[](auto& x) -> void { x += "-ish";  }}; 
-    std::ranges::for_each(view, std::move(callback));
+    std::ranges::for_each(vec, std::move(callback));
 
-    for ( auto const& str : view ) 
+    for ( auto const& str : vec ) 
         std::cout << str << "\n";
 }
 
diff --git a/regression-tests/test-results/mixed-function-expression-with-pointer-capture.cpp b/regression-tests/test-results/mixed-function-expression-with-pointer-capture.cpp
@@ -27,17 +27,16 @@
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2023"}; 
-    std::span view {vec}; 
 
     std::string y {"\n"}; 
-    std::ranges::for_each(view, [_0 = (&y)](auto const& x) -> void { 
+    std::ranges::for_each(vec, [_0 = (&y)](auto const& x) -> void { 
         std::cout << CPP2_UFCS_0(c_str, (*cpp2::assert_not_null(_0))) << x << *cpp2::assert_not_null(_0);  }
     );
 
     auto callback {[](auto& x) -> void { x += "-ish";  }}; 
-    std::ranges::for_each(view, std::move(callback));
+    std::ranges::for_each(vec, std::move(callback));
 
-    for ( auto const& str : view ) 
+    for ( auto const& str : vec ) 
         std::cout << str << "\n";
 }
 
diff --git a/regression-tests/test-results/mixed-function-expression-with-repeated-capture.cpp b/regression-tests/test-results/mixed-function-expression-with-repeated-capture.cpp
@@ -27,16 +27,15 @@
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2022"}; 
-    std::span view {vec}; 
 
     auto y {"\n"}; 
     std::ranges::for_each
-        (view, [_0 = std::move(y)](auto const& x) -> void { std::cout << _0 << x << _0;  });
+        (vec, [_0 = std::move(y)](auto const& x) -> void { std::cout << _0 << x << _0;  });
 
     auto callback {[](auto& x) -> void { x += "-ish";  }}; 
-    std::ranges::for_each(view, std::move(callback));
+    std::ranges::for_each(vec, std::move(callback));
 
-    for ( auto const& str : view ) 
+    for ( auto const& str : vec ) 
         std::cout << str << "\n";
 }
 
diff --git a/regression-tests/test-results/mixed-type-safety-1.cpp b/regression-tests/test-results/mixed-type-safety-1.cpp
@@ -55,7 +55,7 @@ auto print(cpp2::in<std::string> msg, cpp2::in<bool> b) -> void
     print( "1   is int? ", cpp2::is<int>(1));
 
     auto c {cpp2_new<Circle>()}; // safe by construction
-    Shape* s {CPP2_UFCS_0(get, c)}; // safe by Lifetime
+    Shape* s {CPP2_UFCS_0(get, std::move(c))}; // safe by Lifetime
     print("\ns* is Shape?  ", cpp2::is<Shape>(*cpp2::assert_not_null(s)));
     print(  "s* is Circle? ", cpp2::is<Circle>(*cpp2::assert_not_null(s)));
     print(  "s* is Square? ", cpp2::is<Square>(*cpp2::assert_not_null(std::move(s))));
diff --git a/regression-tests/test-results/mixed-ufcs-multiple-template-arguments.cpp b/regression-tests/test-results/mixed-ufcs-multiple-template-arguments.cpp
@@ -38,7 +38,7 @@ struct X {
     std::string test_string {"The rain in Spain flows mainly down the drain"}; 
     std::cout << substr<4,8>(test_string) << "\n";
 
-    X x {test_string}; 
+    X x {std::move(test_string)}; 
     std::cout << CPP2_UFCS_TEMPLATE_0(substr, (<4,8>), std::move(x)) << "\n";
 }
 
diff --git a/regression-tests/test-results/pure2-bounds-safety-span.cpp b/regression-tests/test-results/pure2-bounds-safety-span.cpp
@@ -14,7 +14,7 @@
 #line 2 "pure2-bounds-safety-span.cpp2"
 [[nodiscard]] auto main() -> int;
 
-#line 14 "pure2-bounds-safety-span.cpp2"
+#line 15 "pure2-bounds-safety-span.cpp2"
 auto print_and_decorate(auto const& thing) -> void;
     
 
@@ -28,6 +28,7 @@ auto print_and_decorate(auto const& thing) -> void;
     std::vector<std::string> words {"decorated", "hello", "world"}; 
 
     std::span<std::string> s {words}; 
+    static_cast<void>(std::move(words));
 
     auto i {0}; 
     for( ; cpp2::cmp_less(i,CPP2_UFCS_0(ssize, s)); ++i ) {
diff --git a/regression-tests/test-results/pure2-intro-example-hello-2022.cpp b/regression-tests/test-results/pure2-intro-example-hello-2022.cpp
@@ -13,11 +13,11 @@
 [[nodiscard]] auto main() -> int;
     
 
-#line 12 "pure2-intro-example-hello-2022.cpp2"
+#line 11 "pure2-intro-example-hello-2022.cpp2"
 [[nodiscard]] auto decorate(auto& thing) -> int;
     
 
-#line 17 "pure2-intro-example-hello-2022.cpp2"
+#line 16 "pure2-intro-example-hello-2022.cpp2"
 auto print_it(auto const& x, auto const& len) -> void;
     
 
@@ -26,9 +26,8 @@ auto print_it(auto const& x, auto const& len) -> void;
 [[nodiscard]] auto main() -> int{
     std::vector<std::string> vec {
             "hello", "2022"}; 
-    std::span view {vec}; 
 
-    for ( auto& str : view ) {
+    for ( auto& str : vec ) {
         auto len {decorate(str)}; 
         print_it(str, len);
     }
diff --git a/source/to_cpp1.h b/source/to_cpp1.h
@@ -2100,6 +2100,7 @@ class cppfront
     {
         assert(n.identifier);
         in_non_rvalue_context.push_back(true);
+        auto guard = finally([&]{ in_non_rvalue_context.pop_back(); });
 
         iteration_statements.push_back({ &n, false});
         auto labelname = labelized_position(n.label);
@@ -2134,8 +2135,6 @@ class cppfront
             if (!labelname.empty()) {
                 printer.print_extra(" CPP2_CONTINUE_BREAK("+labelname+") }");
             }
-
-            in_non_rvalue_context.pop_back();
         }
 
         //  Handle do
@@ -2166,8 +2165,6 @@ class cppfront
                 printer.print_cpp2(" ; return true; }() ", n.position());
             }
             printer.print_cpp2(");", n.position());
-
-            in_non_rvalue_context.pop_back();
         }
 
         //  Handle for
@@ -2214,8 +2211,6 @@ class cppfront
             if (!labelname.empty()) {
                 printer.print_extra(" CPP2_CONTINUE_BREAK("+labelname+") }");
             }
-
-            in_non_rvalue_context.pop_back();
         }
 
         else {
@@ -6217,7 +6212,6 @@ class cppfront
             //  If there's an initializer, emit it
             if (n.initializer)
             {
-                in_non_rvalue_context.push_back(true);
                 printer.add_pad_in_this_line(-100);
                 if (type->is_concept()) {
                     printer.print_cpp2( " = ", n.position() );
@@ -6233,7 +6227,6 @@ class cppfront
                 if (!type->is_concept()) {
                     printer.print_cpp2( "}", n.position() );
                 }
-                in_non_rvalue_context.pop_back();
             }
 
             printer.print_cpp2( "; ", n.position() );
