Fix richio vprint

stdlib checks do not allow dereferencing the first element of a vector
when there are no elements in the vector (regardless of whether we have
allocated memory for them).  This whole function is rather
over-engineered, setting up multiple allocations and branches depending
of the string size.  This commit reduces the function to the actions
needed (get the string size, print it into the output)

common/richio.cpp

@@ -48,35 +48,17 @@
 
 static int vprint( std::string* result, const char* format, va_list ap )
 {
-    char    msg[512];
-    // This function can call vsnprintf twice.
-    // But internally, vsnprintf retrieves arguments from the va_list identified by arg as if
-    // va_arg was used on it, and thus the state of the va_list is likely to be altered by the call.
-    // see: www.cplusplus.com/reference/cstdio/vsnprintf
-    // we make a copy of va_list ap for the second call, if happens
     va_list tmp;
     va_copy( tmp, ap );
+    size_t  len = vsnprintf( nullptr, 0, format, tmp );
+    va_end( tmp );
 
-    size_t  len = vsnprintf( msg, sizeof(msg), format, ap );
+    // Resize the output to hold the required data
+    size_t  size = result->size();
+    result->resize( size + len );
 
-    if( len < sizeof(msg) )     // the output fit into msg
-    {
-        result->append( msg, msg + len );
-    }
-    else
-    {
-        // output was too big, so now incur the expense of allocating
-        // a buf for holding suffient characters.
-
-        std::vector<char>   buf;
-        buf.reserve( len+1 );   // reserve(), not resize() which writes. +1 for trailing nul.
-
-        len = vsnprintf( &buf[0], len+1, format, tmp );
-
-        result->append( &buf[0], &buf[0] + len );
-    }
-
-    va_end( tmp );      // Release the temporary va_list, initialised from ap
+    // Now do the actual printing
+    len = vsnprintf( result->data() + size, len + 1, format, ap );
 
     return len;
 }

qa/tests/common/CMakeLists.txt

@@ -43,6 +43,7 @@ set( QA_COMMON_SRCS
     test_kiid.cpp
     test_property.cpp
     test_refdes_utils.cpp
+    test_richio.cpp
     test_text_attributes.cpp
     test_title_block.cpp
     test_types.cpp

qa/tests/common/test_richio.cpp

@@ -0,0 +1,77 @@
+/*
+ * This program source code file is part of KiCad, a free EDA CAD application.
+ *
+ * Copyright (C) 2023 KiCad Developers, see AUTHORS.TXT for contributors.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you may find one here:
+ * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+ * or you may search the http://www.gnu.org website for the version 2 license,
+ * or you may write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+ */
+
+/**
+ * @file
+ * Test suite for general string functions
+ */
+
+#include <qa_utils/wx_utils/unit_test_utils.h>
+
+// Code under test
+#include <richio.h>
+
+/**
+ * Declare the test suite
+ */
+BOOST_AUTO_TEST_SUITE( RichIO )
+
+/**
+ * Test the #vprint method.
+ */
+BOOST_AUTO_TEST_CASE( VPrint )
+{
+    std::string output;
+
+    // Test 1: Basic strings and numbers
+    StrPrintf( &output, "Hello %s! ", "World" );
+    StrPrintf( &output, "Number: %d, ", 42 );
+    StrPrintf( &output, "Float: %.2f, ", 3.14 );
+    StrPrintf( &output, "Char: %c. ", 'A' );
+    BOOST_CHECK_EQUAL( output, std::string( "Hello World! Number: 42, Float: 3.14, Char: A. " ) );
+    output.clear();
+
+    // Test 2: Large string
+    std::string longString( 500, 'A' );
+    StrPrintf( &output, "%s", longString.c_str() );
+    BOOST_CHECK_EQUAL( output, longString );
+    output.clear();
+
+    // Test 3: Edge case with zero characters
+    StrPrintf( &output, "" );
+    BOOST_ASSERT( output.empty() );
+
+    // Test 4: Mixing small and large strings
+    StrPrintf( &output, "Small, " );
+    StrPrintf( &output, "%s, ", longString.c_str() );
+    StrPrintf( &output, "End." );
+    BOOST_CHECK_EQUAL( output, std::string( "Small, " + longString + ", End." ) );
+    output.clear();
+
+    // Test 5: Formatting with various data types
+    StrPrintf( &output, "%d %s %c %.2f", 123, "Hello", 'X', 9.876 );
+    BOOST_CHECK_EQUAL( output, std::string( "123 Hello X 9.88" ) );
+    output.clear();
+}
+
+BOOST_AUTO_TEST_SUITE_END()