<chrono>: Fix formatter ignoring dynamically provided width (#4283)

Co-authored-by: Stephan T. Lavavej <[email protected]>

stl/inc/chrono

@@ -5477,7 +5477,14 @@ namespace chrono {
 
             int _Estimated_width = -1;
             (void) _Measure_string_prefix(_Stream.view(), _Estimated_width);
-            return _Write_aligned(_STD move(_FormatCtx.out()), _Estimated_width, _Specs, _Fmt_align::_Left,
+
+            auto _Format_specs = _Specs;
+            if (_Specs._Dynamic_width_index >= 0) {
+                _Format_specs._Width = _Get_dynamic_specs<_Width_checker>(
+                    _FormatCtx.arg(static_cast<size_t>(_Specs._Dynamic_width_index)));
+            }
+
+            return _Write_aligned(_STD move(_FormatCtx.out()), _Estimated_width, _Format_specs, _Fmt_align::_Left,
                 [&](auto _Out) { return _Fmt_write(_STD move(_Out), _Stream.view()); });
         }
 

tests/std/test.lst

@@ -234,6 +234,7 @@ tests\GH_003840_tellg_when_reading_lf_file_in_text_mode
 tests\GH_003867_output_nan
 tests\GH_004023_mdspan_fwd_prod_overflow
 tests\GH_004040_container_nonmember_functions
+tests\GH_004201_chrono_formatter
 tests\GH_004275_seeking_fancy_iterators
 tests\LWG2381_num_get_floating_point
 tests\LWG2597_complex_branch_cut

tests/std/tests/GH_004201_chrono_formatter/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\concepts_20_matrix.lst

tests/std/tests/GH_004201_chrono_formatter/test.cpp

@@ -0,0 +1,16 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <chrono>
+#include <format>
+#include <string>
+
+using namespace std::literals::chrono_literals;
+
+int main() {
+    assert(std::format("[{:20%T}]", 314159s) == "[87:15:59            ]");
+
+    // std::formatter specializations for <chrono> types used to ignore dynamically provided width
+    assert(std::format("[{:{}%T}]", 314159s, 20) == "[87:15:59            ]");
+}