Prevent crash when custom streambuf implementation throws

stl/inc/xiosbase

@@ -454,7 +454,7 @@ public:
 
     static void __CLRCALL_PURE_OR_CDECL _Addstd(ios_base*); // add standard stream
 
-    size_t _Stdstr; // if > 0 index of standard stream to suppress destruction
+    size_t _Stdstr{0}; // if > 0 index of standard stream to suppress destruction
 
 protected:
     __CLR_OR_THIS_CALL ios_base() {}
@@ -547,9 +547,9 @@ private:
     fmtflags _Fmtfl; // format flags
     streamsize _Prec; // field precision
     streamsize _Wide; // field width
-    _Iosarray* _Arr; // pointer to first node of long/pointer array
-    _Fnarray* _Calls; // pointer to first node of call list
-    locale* _Ploc; // pointer to locale
+    _Iosarray* _Arr{nullptr}; // pointer to first node of long/pointer array
+    _Fnarray* _Calls{nullptr}; // pointer to first node of call list
+    locale* _Ploc{nullptr}; // pointer to locale
 
     __PURE_APPDOMAIN_GLOBAL static int _Index;
     __PURE_APPDOMAIN_GLOBAL static bool _Sync;

stl/src/ios.cpp

@@ -31,6 +31,7 @@ void __CLRCALL_PURE_OR_CDECL ios_base::_Ios_base_dtor(ios_base* _This) { // dest
     }
 
     _This->_Tidy();
+
     delete _This->_Ploc;
 }
 

tests/std/test.lst

@@ -168,6 +168,7 @@ tests\GH_001017_discrete_distribution_out_of_range
 tests\GH_001059_hyperbolic_truncation
 tests\GH_001086_partial_sort_copy
 tests\GH_001103_countl_zero_correctness
+tests\GH_001105_custom_streambuf_throws
 tests\GH_001123_random_cast_out_of_range
 tests\LWG2597_complex_branch_cut
 tests\LWG3018_shared_ptr_function

tests/std/tests/GH_001105_custom_streambuf_throws/env.lst

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

tests/std/tests/GH_001105_custom_streambuf_throws/test.cpp

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <istream>
+#include <stdexcept>
+
+struct bad_buf : std::streambuf {
+    bad_buf() {
+        throw std::runtime_error("throw in constructor!");
+    }
+};
+
+struct custom_stream : std::istream {
+    custom_stream() : std::istream(new bad_buf{}) {}
+};
+
+int main() {
+
+    {
+        // GH-1105 std::istream destructor should not crash if custom streambuf implementation throws.
+        try {
+            custom_stream f{};
+        } catch (const std::runtime_error&) {
+            assert(true);
+        }
+    }
+
+    return 0;
+}