Disable path validation, add warning (#10045)

This is primarily being done to unblock #9223.

Prior to this, we'd validate that the user's `startingDirectory` existed
here. If it was invalid, we'd gracefully fall back to `%USERPROFILE%`.

However, that could cause hangs when combined with WSL. When the WSL
filesystem is slow to respond, we'll end up waiting indefinitely for
their filesystem driver to respond. This can result in the whole terminal
becoming unresponsive.

Similarly, with #9223 we want users to be able to specify WSL paths in a
profile, but this bit of validation logic totally prevents that from working,
because it'll just replace the path with `%USERPROFILE%`.

If the path is eventually invalid, we'll display warning in the
`ConptyConnection`, when the process fails to launch.

Closes #9541
Closes #9114

![image](https://user-images.githubusercontent.com/18356694/117318675-426d2d00-ae50-11eb-9cc0-0b23c397472c.png)

src/cascadia/TerminalConnection/ConptyConnection.cpp

@@ -300,8 +300,20 @@ namespace winrt::Microsoft::Terminal::TerminalConnection::implementation
         // EXIT POINT
         const auto hr = wil::ResultFromCaughtException();
 
-        winrt::hstring failureText{ fmt::format(std::wstring_view{ RS_(L"ProcessFailedToLaunch") }, gsl::narrow_cast<unsigned long>(hr), _commandline) };
+        winrt::hstring failureText{ fmt::format(std::wstring_view{ RS_(L"ProcessFailedToLaunch") },
+                                                gsl::narrow_cast<unsigned long>(hr),
+                                                _commandline) };
         _TerminalOutputHandlers(failureText);
+
+        // If the path was invalid, let's present an informative message to the user
+        if (hr == HRESULT_FROM_WIN32(ERROR_DIRECTORY))
+        {
+            winrt::hstring badPathText{ fmt::format(std::wstring_view{ RS_(L"BadPathText") },
+                                                    _startingDirectory) };
+            _TerminalOutputHandlers(L"\r\n");
+            _TerminalOutputHandlers(badPathText);
+        }
+
         _transitionToState(ConnectionState::Failed);
 
         // Tear down any state we may have accumulated.

src/cascadia/TerminalConnection/Resources/en-US/Resources.resw

@@ -212,4 +212,8 @@
     <comment>The first argument {0...} is the hexadecimal error code. The second argument {1} is the user-specified path to a program.
       If this string is broken to multiple lines, it will not be displayed properly.</comment>
   </data>
-</root>
+  <data name="BadPathText" xml:space="preserve">
+    <value>Could not access starting directory "{0}"</value>
+    <comment>The first argument {0} is a path to a directory on the filesystem, as provided by the user.</comment>
+  </data>
+</root>

src/cascadia/TerminalSettingsModel/Profile.cpp

@@ -413,21 +413,17 @@ std::wstring Profile::EvaluateStartingDirectory(const std::wstring& directory)
     std::unique_ptr<wchar_t[]> evaluatedPath = std::make_unique<wchar_t[]>(numCharsInput);
     THROW_LAST_ERROR_IF(0 == ExpandEnvironmentStrings(directory.c_str(), evaluatedPath.get(), numCharsInput));
 
-    // Validate that the resulting path is legitimate
-    const DWORD dwFileAttributes = GetFileAttributes(evaluatedPath.get());
-    if ((dwFileAttributes != INVALID_FILE_ATTRIBUTES) && (WI_IsFlagSet(dwFileAttributes, FILE_ATTRIBUTE_DIRECTORY)))
-    {
-        return std::wstring(evaluatedPath.get(), numCharsInput);
-    }
-    else
-    {
-        // In the event where the user supplied a path that can't be resolved, use a reasonable default (in this case, %userprofile%)
-        const DWORD numCharsDefault = ExpandEnvironmentStrings(DEFAULT_STARTING_DIRECTORY.c_str(), nullptr, 0);
-        std::unique_ptr<wchar_t[]> defaultPath = std::make_unique<wchar_t[]>(numCharsDefault);
-        THROW_LAST_ERROR_IF(0 == ExpandEnvironmentStrings(DEFAULT_STARTING_DIRECTORY.c_str(), defaultPath.get(), numCharsDefault));
-
-        return std::wstring(defaultPath.get(), numCharsDefault);
-    }
+    // Prior to GH#9541, we'd validate that the user's startingDirectory existed
+    // here. If it was invalid, we'd gracefully fall back to %USERPROFILE%.
+    //
+    // However, that could cause hangs when combined with WSL. When the WSL
+    // filesystem is slow to respond, we'll end up waiting indefinitely for
+    // their filesystem driver to respond. This can result in the whole terminal
+    // becoming unresponsive.
+    //
+    // If the path is eventually invalid, we'll display warning in the
+    // ConptyConnection when the process fails to launch.
+    return std::wstring(evaluatedPath.get(), numCharsInput);
 }
 
 // Function Description: