From ae2b05be5c594ddcdf607b06d483de7aa7449a45 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Tue, 31 Oct 2023 00:04:27 +0100
Subject: [PATCH] Fix more compatibility problems in C++17 wxString::ToLong()

Unlike the traditional C functions, std::from_chars() doesn't skip
leading whitespace and doesn't accept the leading "+" sign, so we need
to skip them explicitly to preserve the behaviour of ToLong() in the
previous wxWidgets versions.
---
 src/common/string.cpp     | 24 +++++++++++++++++-------
 tests/strings/strings.cpp |  3 +++
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/common/string.cpp b/src/common/string.cpp
index bcd78b67bd..f2949268e3 100644
--- a/src/common/string.cpp
+++ b/src/common/string.cpp
@@ -1580,15 +1580,25 @@ bool wxString::ToDouble(double *pVal) const
 namespace
 {
 
-// Helper of ToCLong() and ToCULong() taking care of base-related stuff:
-// because from_chars() doesn't recognize base==0 and doesn't recognize "0x"
-// prefix even if base 16 is explicitly specified, we need to skip the prefix
-// indicating the base to use if it's present and adjust "base" itself instead.
+// Helper of ToCLong() and ToCULong() taking care of prefix and base-related
+// stuff: because from_chars() doesn't skip leading whitespace and doesn't
+// recognize base==0 nor "0x" prefix even if base 16 is explicitly specified,
+// we need to skip the leading space and prefix indicating the base to use if
+// it's present and adjust "base" itself instead.
 //
 // Return false if base is already specified but is incompatible with the
 // prefix used.
-bool SetBaseAndSkipPrefix(int& base, const char*& start, const char* end)
+bool SkipOptPrefixAndSetBase(int& base, const char*& start, const char* end)
 {
+    // Start by skipping whitespace.
+    while ( wxSafeIsspace(*start) )
+        ++start;
+
+    // Also skip optional "+" which std::from_chars() doesn't accept neither.
+    if ( *start == '+' )
+        ++start;
+
+    // Then check for the base prefix.
     if ( end - start > 1 && *start == '0' )
     {
         ++start;
@@ -1623,7 +1633,7 @@ bool wxString::ToCLong(long *pVal, int base) const
     auto start = buf.data();
     const auto end = start + buf.length();
 
-    if ( !SetBaseAndSkipPrefix(base, start, end) )
+    if ( !SkipOptPrefixAndSetBase(base, start, end) )
         return false;
 
     const auto res = std::from_chars(start, end, *pVal, base);
@@ -1639,7 +1649,7 @@ bool wxString::ToCULong(unsigned long *pVal, int base) const
     auto start = buf.data();
     const auto end = start + buf.length();
 
-    if ( !SetBaseAndSkipPrefix(base, start, end) )
+    if ( !SkipOptPrefixAndSetBase(base, start, end) )
         return false;
 
     // Extra complication: for compatibility reasons, this function does accept
diff --git a/tests/strings/strings.cpp b/tests/strings/strings.cpp
index 43afe86eba..e8f0550a3f 100644
--- a/tests/strings/strings.cpp
+++ b/tests/strings/strings.cpp
@@ -580,6 +580,9 @@ static const struct ToLongData
     { wxT("-1"), -1, Number_Signed | Number_Long },
     // this is surprising but consistent with strtoul() behaviour
     { wxT("-1"), (TestValue_t)ULONG_MAX, Number_Unsigned | Number_Long },
+    // a couple of edge cases
+    { wxT(" +1"), 1, Number_Ok },
+    { wxT(" -1"), (TestValue_t)ULONG_MAX, Number_Unsigned | Number_Long },
 
     // this must overflow, even with 64 bit long
     { wxT("922337203685477580711"), 0, Number_Invalid },