[llvm] [Support] Report EISDIR when opening a directory (PR #79880)

[James Henderson via llvm-commits]

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@@ -1296,6 +1296,29 @@ TEST_F(FileSystemTest, UTF8ToUTF16DirectoryIteration) {
 }
 #endif
 
+TEST_F(FileSystemTest, OpenDirectoryAsFileForRead) {
+  std::string Buf(5, '?');
+  Expected<fs::file_t> FD = fs::openNativeFileForRead(TestDirectory);
+#ifdef _WIN32
+  ASSERT_EQ(errorToErrorCode(BytesRead.takeError()), errc::is_a_directory);
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jh7370 wrote:

Windows build is failing here. It's quite hard to check the state of an `Expected` when it's not been declared yet...

https://github.com/llvm/llvm-project/pull/79880