Allow exporting to hidden files

doc/ReleaseNotes.md

@@ -49,6 +49,7 @@ The PowerShell module now automatically uses `GH_TOKEN` or `GITHUB_TOKEN` enviro
 
 ## Bug Fixes
 
+* `winget export` now works when the destination path is a hidden file
 * Fixed the `useLatest` property in the DSC v3 `Microsoft.WinGet/Package` resource schema to emit a boolean default (`false`) instead of the incorrect string `"false"`.
 * `SignFile` in `WinGetSourceCreator` now supports an optional RFC 3161 timestamp server via the new `TimestampServer` property on the `Signature` model. When set, `signtool.exe` is called with `/tr <url> /td sha256`, embedding a countersignature timestamp so that signed packages remain valid after the signing certificate expires.
 * File and directory paths passed to `signtool.exe` and `makeappx.exe` are now quoted, fixing failures when paths contain spaces.

src/AppInstallerCLICore/Workflows/ImportExportFlow.cpp

@@ -7,6 +7,7 @@
 #include "PackageCollection.h"
 #include "DependenciesFlow.h"
 #include "WorkflowBase.h"
+#include <winget/Filesystem.h>
 #include <winget/RepositorySearch.h>
 #include <winget/Runtime.h>
 #include <winget/PackageVersionSelection.h>
@@ -177,8 +178,21 @@ namespace AppInstaller::CLI::Workflow
         auto packages = PackagesJson::CreateJson(context.Get<Execution::Data::PackageCollection>());
 
         std::filesystem::path outputFilePath{ context.Args.GetArg(Execution::Args::Type::OutputFile) };
-        std::ofstream outputFileStream{ outputFilePath };
-        outputFileStream << packages;
+
+        // GetFileAttributesW returns INVALID_FILE_ATTRIBUTES for nonexistent files, so no separate exists() check is needed.
+        DWORD attrs = GetFileAttributesW(outputFilePath.c_str());
+        bool isHidden = (attrs != INVALID_FILE_ATTRIBUTES && (attrs & FILE_ATTRIBUTE_HIDDEN));
+
+        // Open the file directly without changing its attributes:
+        // - For an existing hidden file, use TRUNCATE_EXISTING to clear its content while preserving its attributes.
+        // - Otherwise, use CREATE_ALWAYS to create a new file or overwrite an existing one.
+        DWORD creationDisposition = isHidden ? TRUNCATE_EXISTING : CREATE_ALWAYS;
+        wil::unique_hfile fileHandle{ CreateFileW(outputFilePath.c_str(), GENERIC_WRITE, 0, nullptr, creationDisposition, FILE_ATTRIBUTE_NORMAL, nullptr) };
+        THROW_LAST_ERROR_IF(!fileHandle);
+
+        Json::StreamWriterBuilder writerBuilder;
+        std::string jsonContent = Json::writeString(writerBuilder, packages);
+        Filesystem::WriteStringToFile(fileHandle.get(), jsonContent);
     }
 
     void ReadImportFile(Execution::Context& context)

src/AppInstallerCLITests/Filesystem.cpp

@@ -224,6 +224,56 @@ TEST_CASE("PathTree_VisitIf_Correct", "[filesystem][pathtree]")
     pathTree.VisitIf(L"C:", check_input, if_input);
 }
 
+TEST_CASE("WriteStringToFile", "[filesystem]")
+{
+    SECTION("Basic content")
+    {
+        TestCommon::TempDirectory tempDirectory{ "WriteStringToFile" };
+        auto tempFile = tempDirectory.CreateTempFile("output", ".txt");
+        wil::unique_hfile fileHandle{ CreateFileW(tempFile.GetPath().c_str(), GENERIC_WRITE, 0, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr) };
+        REQUIRE(fileHandle);
+
+        std::string content = "Hello, WinGet!";
+        REQUIRE_NOTHROW(WriteStringToFile(fileHandle.get(), content));
+        fileHandle.reset();
+
+        std::ifstream readBack{ tempFile.GetPath() };
+        std::string result{ std::istreambuf_iterator<char>(readBack), std::istreambuf_iterator<char>() };
+        REQUIRE(result == content);
+    }
+
+    SECTION("Empty content")
+    {
+        TestCommon::TempDirectory tempDirectory{ "WriteStringToFile" };
+        auto tempFile = tempDirectory.CreateTempFile("empty", ".txt");
+        wil::unique_hfile fileHandle{ CreateFileW(tempFile.GetPath().c_str(), GENERIC_WRITE, 0, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr) };
+        REQUIRE(fileHandle);
+
+        REQUIRE_NOTHROW(WriteStringToFile(fileHandle.get(), ""));
+        fileHandle.reset();
+
+        std::ifstream readBack{ tempFile.GetPath() };
+        std::string result{ std::istreambuf_iterator<char>(readBack), std::istreambuf_iterator<char>() };
+        REQUIRE(result.empty());
+    }
+
+    SECTION("Large content")
+    {
+        TestCommon::TempDirectory tempDirectory{ "WriteStringToFile" };
+        auto tempFile = tempDirectory.CreateTempFile("large", ".txt");
+        wil::unique_hfile fileHandle{ CreateFileW(tempFile.GetPath().c_str(), GENERIC_WRITE, 0, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr) };
+        REQUIRE(fileHandle);
+
+        std::string content(1 << 20, 'x'); // 1 MiB of 'x'
+        REQUIRE_NOTHROW(WriteStringToFile(fileHandle.get(), content));
+        fileHandle.reset();
+
+        std::ifstream readBack{ tempFile.GetPath() };
+        std::string result{ std::istreambuf_iterator<char>(readBack), std::istreambuf_iterator<char>() };
+        REQUIRE(result == content);
+    }
+}
+
 TEST_CASE("GetFileInfoFor", "[filesystem]")
 {
     TestCommon::TempDirectory tempDirectory{ "GetFileInfoFor" };

src/AppInstallerSharedLib/Filesystem.cpp

@@ -565,4 +565,20 @@ namespace AppInstaller::Filesystem
 
         files.resize(i);
     }
+
+    void WriteStringToFile(HANDLE fileHandle, std::string_view content)
+    {
+        size_t totalBytesWritten = 0;
+        while (totalBytesWritten < content.size())
+        {
+            DWORD bytesWritten = 0;
+            THROW_LAST_ERROR_IF(!WriteFile(
+                fileHandle,
+                content.data() + totalBytesWritten,
+                static_cast<DWORD>(content.size() - totalBytesWritten),
+                &bytesWritten,
+                nullptr));
+            totalBytesWritten += bytesWritten;
+        }
+    }
 }

src/AppInstallerSharedLib/Public/winget/Filesystem.h

@@ -4,6 +4,7 @@
 #include <filesystem>
 #include <map>
 #include <optional>
+#include <string_view>
 #include <vector>
 #include <shtypes.h>
 
@@ -148,4 +149,7 @@ namespace AppInstaller::Filesystem
 
     // Modifies the given files to only include those that exceed the limits that are provided.
     void FilterToFilesExceedingLimits(std::vector<FileInfo>& files, const FileLimits& limits);
+
+    // Writes the given string to the file handle, handling partial writes.
+    void WriteStringToFile(HANDLE fileHandle, std::string_view content);
 }