Add helper: getAccessibleChildren (PR #13126)

Make all usages of AccessibleChildren conform to a consistent approach.
Management of resources is automatic.
Related to #13106

nvdaHelper/common/ia2utils.cpp

@@ -74,6 +74,37 @@ void IA2AttribsToMap(const wstring &attribsString, map<wstring, wstring> &attrib
 	}
 }
 
+std::pair<std::vector<CComVariant>, HRESULT>
+getAccessibleChildren(IAccessible* pacc, long indexOfFirstChild, long maxChildCount) {
+	try {
+		std::vector<CComVariant> varChildren(maxChildCount);
+		const auto res = AccessibleChildren(
+			pacc,
+			indexOfFirstChild,
+			maxChildCount,
+			varChildren.data(),
+			&maxChildCount
+		);
+		if (res != S_OK) {
+			return std::make_pair(
+				std::vector<CComVariant>(0),
+				res
+			);
+		}
+		// shrink the vector in case less children were returned.
+		// so that varChildren.size() will equal actual filled size
+		varChildren.resize(maxChildCount);
+		// no need to shrink to fit, make_pair will copy the vector, using only the first varChildren.size() elements.
+		return std::make_pair(varChildren, S_OK);
+	}
+	catch (std::bad_array_new_length&) {
+		return std::make_pair(
+			std::vector<CComVariant>(0),
+			S_FALSE
+		);
+	}
+}
+
 CComPtr<IAccessibleHyperlink> HyperlinkGetter::next() {
 	return this->get(this->index++);
 }

nvdaHelper/common/ia2utils.h

@@ -18,6 +18,8 @@ This license can be found at:
 #include <atlcomcli.h>
 #include <string>
 #include <map>
+#include <vector>
+#include <utility>
 #include <memory>
 #include <ia2.h>
 
@@ -34,6 +36,12 @@ bool fetchIA2Attributes(IAccessible2* pacc2, std::map<std::wstring, std::wstring
  */
 void IA2AttribsToMap(const std::wstring &attribsString, std::map<std::wstring, std::wstring> &attribsMap);
 
+/**
+* Helper to collect the children for an IAccessible, uses memory managed types that will clear / delete automatically.
+*/
+std::pair<std::vector<CComVariant>, HRESULT>
+getAccessibleChildren(IAccessible* pacc, long indexOfFirstChild, long maxChildCount);
+
 /**
  * Base class to support retrieving hyperlinks (embedded objects) from
  * IAccessibleHypertext or IAccessibleHypertext2.

nvdaHelper/vbufBackends/adobeAcrobat/adobeAcrobat.cpp

@@ -17,6 +17,7 @@ This license can be found at:
 #include <iomanip>
 #include <windows.h>
 #include <oleacc.h>
+#include <common/ia2utils.h>
 #include <remote/nvdaHelperRemote.h>
 #include <vbufBase/backend.h>
 #include <common/log.h>
@@ -619,30 +620,22 @@ AdobeAcrobatVBufStorage_controlFieldNode_t* AdobeAcrobatVBufBackend_t::fillVBuf(
 
 	} else if (childCount > 0) {
 		// Iterate through the children.
-		LOG_DEBUG(L"Allocate memory to hold children");
-		VARIANT* varChildren;
-		if((varChildren=(VARIANT*)malloc(sizeof(VARIANT)*childCount))==NULL) {
-			LOG_DEBUG(L"Error allocating varChildren memory");
-			if (stdName)
-				SysFreeString(stdName);
-			return NULL;
-		}
 		LOG_DEBUG(L"Fetch children with AccessibleChildren");
-		if((res=AccessibleChildren(pacc,0,childCount,varChildren,(long*)(&childCount)))!=S_OK) {
-			LOG_DEBUG(L"AccessibleChildren returned "<<res);
+		auto[varChildren, accChildRes] = getAccessibleChildren(pacc, 0, childCount);
+		if(S_OK != accChildRes || varChildren.size() == 0) {
+			LOG_DEBUG(L"Failed to get AccessibleChildren (count: " << childCount << L"), res: " << accChildRes);
 			childCount=0;
 		}
-		LOG_DEBUG(L"got "<<childCount<<L" children");
-		for(int i=0;i<childCount;++i) {
-			LOG_DEBUG(L"child "<<i);
-			if(varChildren[i].vt==VT_DISPATCH) {
+		LOG_DEBUG(L"got "<< varChildren.size() << L" children");
+		for(auto i = 0u; i < varChildren.size(); ++i) {
+			LOG_DEBUG(L"child " << i);
+			if(VT_DISPATCH == varChildren[i].vt) {
 				LOG_DEBUG(L"QueryInterface dispatch child to IID_IAccesible");
-				IAccessible* childPacc=NULL;
-				if((res=varChildren[i].pdispVal->QueryInterface(IID_IAccessible,(void**)(&childPacc)))!=S_OK) {
-					LOG_DEBUG(L"varChildren["<<i<<L"].pdispVal->QueryInterface to IID_iAccessible returned "<<res);
-					childPacc=NULL;
+				CComQIPtr<IAccessible, &IID_IAccessible> childPacc(varChildren[i].pdispVal);
+				if(!childPacc) {
+					LOG_DEBUG(L"varChildren[" << i << L"]: QueryInterface to IID_iAccessible failed.");
 				}
-				if(childPacc) {
+				else {
 					if (this->isXFA) {
 						// HACK: If this is an XFA document, we must call WindowFromAccessibleObject() so that AccessibleObjectFromEvent() will work for this node.
 						HWND tempHwnd;
@@ -654,15 +647,9 @@ AdobeAcrobatVBufStorage_controlFieldNode_t* AdobeAcrobatVBufBackend_t::fillVBuf(
 					} else {
 						LOG_DEBUG(L"Error in calling fillVBuf");
 					}
-					LOG_DEBUG(L"releasing child IAccessible object");
-					childPacc->Release();
 				}
 			}
-			VariantClear(&(varChildren[i]));
 		}
-		LOG_DEBUG(L"Freeing memory holding children");
-		free(varChildren);
-
 	} else {
 		// No children, so this is a leaf node.
 		if (!this->isXFA && !stdName) {

nvdaHelper/vbufBackends/gecko_ia2/gecko_ia2.cpp

@@ -950,25 +950,20 @@ VBufStorage_fieldNode_t* GeckoVBufBackend_t::fillVBuf(
 
 		} else if (renderChildren && childCount > 0) {
 			// The object has no text, but we do want to render its children.
-			VARIANT* varChildren;
-			if(!(varChildren=(VARIANT*)malloc(sizeof(VARIANT)*childCount))) {
-				LOG_DEBUG(L"Error allocating varChildren memory");
-				return NULL;
+			auto [varChildren, accChildRes] = getAccessibleChildren(pacc, 0, childCount);
+			if (S_OK != accChildRes || varChildren.size() == 0) {
+				LOG_ERROR(L"AccessibleChildren failed (count: " << childCount << L"), res: " << accChildRes);
 			}
-			long accessibleChildrenCount = 0;
-			if(AccessibleChildren(pacc,0,childCount,varChildren,&accessibleChildrenCount)!=S_OK) {
-				LOG_DEBUG(L"AccessibleChildren failed");
-				accessibleChildrenCount=0;
-			}
-			for(long i=0;i<accessibleChildrenCount;++i) {
-				if (varChildren[i].vt != VT_DISPATCH) {
-					VariantClear(&(varChildren[i]));
+			LOG_DEBUG(L"got " << varChildren.size() << L" children");
+
+			for(CComVariant& child : varChildren) {
+				if (child.vt != VT_DISPATCH || !child.pdispVal) {
+					child.Clear();
 					continue;
 				}
-				IAccessible2* childPacc=NULL;
-				if(varChildren[i].pdispVal) varChildren[i].pdispVal->QueryInterface(IID_IAccessible2,(void**)&childPacc);
+				CComQIPtr< IAccessible2, &IID_IAccessible2> childPacc(child.pdispVal);
 				if (!childPacc) {
-					VariantClear(&(varChildren[i]));
+					child.Clear();
 					continue;
 				}
 				tempNode = this->fillVBuf(
@@ -986,11 +981,8 @@ VBufStorage_fieldNode_t* GeckoVBufBackend_t::fillVBuf(
 				}
 				else
 					LOG_DEBUG(L"Error in calling fillVBuf");
-				childPacc->Release();
-				VariantClear(&(varChildren[i]));
+				child.Clear();
 			}
-			free(varChildren);
-
 		} else if (renderSelectedItemOnly) {
 			CComPtr<IAccessible2> item = this->getSelectedItem(pacc, IA2AttribsMap);
 			if (item) {

nvdaHelper/vbufBackends/lotusNotesRichText/lotusNotesRichText.cpp

@@ -17,6 +17,7 @@ This license can be found at:
 #include <windows.h>
 #include <oleacc.h>
 #include <common/log.h>
+#include <common/ia2utils.h>
 #include <remote/nvdaHelperRemote.h>
 #include <vbufBase/backend.h>
 #include "lotusNotesRichText.h"
@@ -170,12 +171,18 @@ void lotusNotesRichTextVBufBackend_t::render(VBufStorage_buffer_t* buffer, int d
 		VBufStorage_fieldNode_t* previousNode=NULL;
 		long childCount=0;
 		pacc->get_accChildCount(&childCount);
-		VARIANT* varChildren=(VARIANT*)malloc(sizeof(VARIANT)*childCount);
-		HRESULT hRes;
-		hRes=AccessibleChildren(pacc,0,childCount,varChildren,&childCount);
-		for(int i=0;i<childCount;++i) {
-			if(varChildren[i].vt==VT_I4) {
-				previousNode=this->renderControlContent(buffer,parentNode,previousNode,docHandle,pacc,varChildren[i].lVal);
+
+		auto [varChildren, hres] = getAccessibleChildren(pacc, 0, childCount);
+		for(CComVariant& child : varChildren) {
+			if(VT_I4 == child.vt) {
+				previousNode = this->renderControlContent(
+					buffer,
+					parentNode,
+					previousNode,
+					docHandle,
+					pacc,
+					child.lVal
+				);
 			}
 		}
 	} else {

nvdaHelper/vbufBackends/webKit/webKit.cpp

@@ -19,6 +19,7 @@ This license can be found at:
 #include <ia2.h>
 #include <remote/nvdaHelperRemote.h>
 #include <common/log.h>
+#include <common/ia2utils.h>
 #include <vbufBase/backend.h>
 #include "webKit.h"
 
@@ -123,20 +124,19 @@ VBufStorage_fieldNode_t* WebKitVBufBackend_t::fillVBuf(int docHandle, IAccessibl
 
 	// Iterate through the children.
 	if (childCount > 0) {
-		auto varChildren = make_unique<CComVariant[]>(childCount);
-		if(AccessibleChildren(pacc,0,childCount,varChildren.get(),(long*)(&childCount))!=S_OK) {
-			childCount=0;
-		}
-		for(int i=0;i<childCount;i++) {
-			if(varChildren[i].vt!=VT_DISPATCH) {
-				continue;
-			}
-			CComQIPtr<IAccessible2> childPacc = varChildren[i].pdispVal;
-			if(!childPacc) {
-				continue;
-			}
-			if((tempNode=this->fillVBuf(docHandle,childPacc,buffer,parentNode,previousNode))!=NULL) {
-				previousNode=tempNode;
+		auto [varChildren, accChildrenRes] = getAccessibleChildren(pacc, 0, childCount);
+		if (S_OK == accChildrenRes) {
+			for (CComVariant& child : varChildren) {
+				if (VT_DISPATCH != child.vt) {
+					continue;
+				}
+				CComQIPtr<IAccessible2> childPacc(child.pdispVal);
+				if (!childPacc) {
+					continue;
+				}
+				if ((tempNode = this->fillVBuf(docHandle, childPacc, buffer, parentNode, previousNode)) != NULL) {
+					previousNode = tempNode;
+				}
 			}
 		}
 	} else {