Avoid calling OString ctor with null pointer

...in preparation of potential future changes from using OString to using
std::string_view, where OString has an undocumented feature of allowing
construction from a null pointer.

This is mostly the result of a manual audit of potentially problematic getenv
calls across the code base.  But there can be other problematic places too, like
the xmlGetProp call in tools/source/xml/XmlWalker.cxx.  To identify those,
rtl_{string,uString}_newFromStr aborts now in non-production debug builds when a
null pointer is passed(and all places that hit with a full `make check
screenshot` have been addressed here).  Once we are confident that all
problematic places have been identified, we should drop support for the
undocumented feature (see the TODO in sal/rtl/strtmpl.cxx).

Change-Id: I595cc6d4f1cda74add2a3db171323f817d362b08
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/107430
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

idl/source/prj/command.cxx

@@ -277,7 +277,8 @@ SvCommand::SvCommand( int argc, char ** argv )
 
     aList.clear();
 
-    OString aInc(getenv("INCLUDE"));
+    auto const env = getenv("INCLUDE");
+    OString aInc(env == nullptr ? "" : env);
     // append include environment variable
     if( aInc.getLength() )
     {

sal/osl/w32/socket.cxx

@@ -512,7 +512,11 @@ oslHostAddr SAL_CALL osl_createHostAddrByName(rtl_uString *strHostname)
             {
                 pRet = static_cast<oslHostAddr>(
                     rtl_allocateZeroMemory(sizeof(struct oslHostAddrImpl)));
-                rtl_uString_newFromStr(&pRet->pHostName, o3tl::toU(pIter->ai_canonname));
+                if (pIter->ai_canonname == nullptr) {
+                    rtl_uString_new(&pRet->pHostName);
+                } else {
+                    rtl_uString_newFromStr(&pRet->pHostName, o3tl::toU(pIter->ai_canonname));
+                }
                 pRet->pSockAddr = createSocketAddr();
                 memcpy(& pRet->pSockAddr->m_sockaddr,
                        pIter->ai_addr, pIter->ai_addrlen);

sal/qa/osl/file/osl_File.cxx

@@ -931,7 +931,7 @@ namespace osl_FileBase
         OString sURL("file://~/tmp");
         char* home_path;
         home_path = getenv("HOME");
-        OString expResult(home_path);
+        OString expResult(home_path ? home_path : "");
         expResult += "/tmp";
         checkUNXBehaviour_getSystemPathFromFileURL(sURL, osl::FileBase::E_None, expResult);
 #endif
@@ -1009,7 +1009,7 @@ namespace osl_FileBase
         OString sSysPath("~/tmp");
         char* home_path;
         home_path = getenv("HOME");
-        OString expResult(home_path);
+        OString expResult(home_path ? home_path : "");
         expResult = "file://"+ expResult + "/tmp";
         checkUNXBehaviour_getFileURLFromSystemPath(sSysPath, osl::FileBase::E_None, expResult);
         checkWNTBehaviour_getFileURLFromSystemPath(sSysPath, osl::FileBase::E_None, "~/tmp");

sal/rtl/strtmpl.cxx

@@ -24,6 +24,7 @@
 
 #include <algorithm>
 #include <cassert>
+#include <cstdlib>
 #include <limits>
 
 #include <cstring>
@@ -1324,6 +1325,15 @@ void SAL_CALL IMPL_RTL_STRINGNAME( newFromStr )( IMPL_RTL_STRINGDATA** ppThis,
     IMPL_RTL_STRINGDATA*    pOrg;
     sal_Int32               nLen;
 
+#if OSL_DEBUG_LEVEL > 0
+    //TODO: For now, only abort in non-production debug builds; once all places that rely on the
+    // undocumented newFromStr behavior of treating a null pCharStr like an empty string have been
+    // found and fixed, drop support for that behavior and turn this into a general assert:
+    if (pCharStr == nullptr) {
+        std::abort();
+    }
+#endif
+
     if ( pCharStr )
     {
         nLen = IMPL_RTL_STRNAME( getLength )( pCharStr );

test/source/screenshot_test.cxx

@@ -47,7 +47,9 @@ ScreenshotTest::ScreenshotTest()
     , maParent(nullptr, "vcl/ui/screenshotparent.ui", "ScreenShot")
     , mxParentWidget(maParent.getDialog()->weld_content_area())
 {
-    maCurrentLanguage = OUString::fromUtf8(getenv("LO_TEST_LOCALE"));
+    if (auto const env = getenv("LO_TEST_LOCALE")) {
+        maCurrentLanguage = OUString::fromUtf8(env);
+    }
 }
 
 ScreenshotTest::~ScreenshotTest()

tools/source/xml/XmlWalker.cxx

@@ -90,7 +90,8 @@ OString XmlWalker::attribute(const OString& sName)
 {
     xmlChar* xmlName = xmlCharStrdup(sName.getStr());
     xmlChar* xmlAttribute = xmlGetProp(mpImpl->mpCurrent, xmlName);
-    OString aAttributeContent(reinterpret_cast<const char*>(xmlAttribute));
+    OString aAttributeContent(
+        xmlAttribute == nullptr ? "" : reinterpret_cast<const char*>(xmlAttribute));
     xmlFree(xmlAttribute);
     xmlFree(xmlName);
 

vcl/headless/svpprn.cxx

@@ -50,7 +50,9 @@ static OUString getPdfDir( const PrinterInfo& rInfo )
             sal_Int32 nPos = 0;
             aDir = aToken.getToken( 1, '=', nPos );
             if( aDir.isEmpty() )
-                aDir = OStringToOUString( OString( getenv( "HOME" ) ), osl_getThreadTextEncoding() );
+                if (auto const env = getenv( "HOME" )) {
+                    aDir = OStringToOUString( OString( env ), osl_getThreadTextEncoding() );
+                }
             break;
         }
     }

vcl/qt5/Qt5Instance_Print.cxx

@@ -50,7 +50,10 @@ static OUString getPdfDir(const PrinterInfo& rInfo)
             sal_Int32 nPos = 0;
             aDir = aToken.getToken(1, '=', nPos);
             if (aDir.isEmpty())
-                aDir = OStringToOUString(OString(getenv("HOME")), osl_getThreadTextEncoding());
+                if (auto const env = getenv("HOME"))
+                {
+                    aDir = OStringToOUString(OString(env), osl_getThreadTextEncoding());
+                }
             break;
         }
     }

vcl/unx/generic/dtrans/X11_selection.cxx

@@ -675,7 +675,9 @@ SelectionManager& SelectionManager::get( const OUString& rDisplayName )
 
     OUString aDisplayName( rDisplayName );
     if( aDisplayName.isEmpty() )
-        aDisplayName = OStringToOUString( getenv( "DISPLAY" ), RTL_TEXTENCODING_ISO_8859_1 );
+        if (auto const env = getenv( "DISPLAY" )) {
+            aDisplayName = OStringToOUString( env, RTL_TEXTENCODING_ISO_8859_1 );
+        }
     SelectionManager* pInstance = nullptr;
 
     std::unordered_map< OUString, SelectionManager* >::iterator it = getInstances().find( aDisplayName );