Fix crash related to unparseable/invalid media resource paths (#4194)

WT crashes when an unparseable/invalid `backgroundImage` or `icon`
resource path is provided in `profiles.json`. This PR averts the crash
by the validating and correcting resource paths as a part of the
`_ValidateSettings()` function in `CascadiaSettings`.
`_ValidateSettings()` is run on start up and any time `profiles.json` is
changed, so a user can not change a file path and avoid the validation
step. 

When a bad `backgroundImage` or `icon` resource path is detected, a
warning screen will be presented.

References #4002, which identified a consistent repro for the crash.

To validate the resource, a `Windows::Foundation::Uri` object is
constructed with the path. The ctor will throw if the resource path is
invalid. Whether or not this validation method is robust enough is a
subject worth review. The correction method for when a bad resource path
is detected is to reset the `std::optional<winrt::hstring>` holding the
file path. 

The text in the warning display was cribbed from the text used when an
invalid `colorScheme` is used. Whether or not the case of a bad
background image file path warrants a warning display is a subject worth
review.

Ensured the repro steps in #4002 did not trigger a crash. Additionally,
some potential backdoor paths to a crash were tested: 

- Deleting the file of a validated background image file path
- Changing the actual file name of a validated background image file
  path
- Replacing the file of a validated background image file path with a
  non-image file (of the same name)
- Using a non-image file as a background image

In all the above cases WT does not crash, and instead defaults to the
background color specified in the profile's `colorScheme`. This PR does
not implement this recovery behavior (existing error catching code
does).

Closes #2329

src/cascadia/TerminalApp/AppLogic.cpp

@@ -27,10 +27,12 @@ namespace winrt
 // !!! IMPORTANT !!!
 // Make sure that these keys are in the same order as the
 // SettingsLoadWarnings/Errors enum is!
-static const std::array<std::wstring_view, 3> settingsLoadWarningsLabels {
+static const std::array<std::wstring_view, 5> settingsLoadWarningsLabels {
     USES_RESOURCE(L"MissingDefaultProfileText"),
     USES_RESOURCE(L"DuplicateProfileText"),
-    USES_RESOURCE(L"UnknownColorSchemeText")
+    USES_RESOURCE(L"UnknownColorSchemeText"),
+    USES_RESOURCE(L"InvalidBackgroundImage"),
+    USES_RESOURCE(L"InvalidIcon")
 };
 static const std::array<std::wstring_view, 2> settingsLoadErrorsLabels {
     USES_RESOURCE(L"NoProfilesText"),

src/cascadia/TerminalApp/CascadiaSettings.cpp

@@ -198,6 +198,10 @@ void CascadiaSettings::_ValidateSettings()
     // just use the hardcoded defaults
     _ValidateAllSchemesExist();
 
+    // Ensure all profile's with specified images resources have valid file path.
+    // This validates icons and background images.
+    _ValidateMediaResources();
+
     // TODO:GH#2548 ensure there's at least one key bound. Display a warning if
     // there's _NO_ keys bound to any actions. That's highly irregular, and
     // likely an indication of an error somehow.
@@ -424,6 +428,64 @@ void CascadiaSettings::_ValidateAllSchemesExist()
     }
 }
 
+// Method Description:
+// - Ensures that all specified images resources (icons and background images) are valid URIs.
+//   This does not verify that the icon or background image files are encoded as an image.
+// Arguments:
+// - <none>
+// Return Value:
+// - <none>
+// - Appends a SettingsLoadWarnings::InvalidBackgroundImage to our list of warnings if
+//   we find any invalid background images.
+// - Appends a SettingsLoadWarnings::InvalidIconImage to our list of warnings if
+//   we find any invalid icon images.
+void CascadiaSettings::_ValidateMediaResources()
+{
+    bool invalidBackground{ false };
+    bool invalidIcon{ false };
+
+    for (auto& profile : _profiles)
+    {
+        if (profile.HasBackgroundImage())
+        {
+            // Attempt to convert the path to a URI, the ctor will throw if it's invalid/unparseable.
+            // This covers file paths on the machine, app data, URLs, and other resource paths.
+            try
+            {
+                winrt::Windows::Foundation::Uri imagePath{ profile.GetExpandedBackgroundImagePath() };
+            }
+            catch (...)
+            {
+                profile.ResetBackgroundImagePath();
+                invalidBackground = true;
+            }
+        }
+
+        if (profile.HasIcon())
+        {
+            try
+            {
+                winrt::Windows::Foundation::Uri imagePath{ profile.GetExpandedIconPath() };
+            }
+            catch (...)
+            {
+                profile.ResetIconPath();
+                invalidIcon = true;
+            }
+        }
+    }
+
+    if (invalidBackground)
+    {
+        _warnings.push_back(::TerminalApp::SettingsLoadWarnings::InvalidBackgroundImage);
+    }
+
+    if (invalidIcon)
+    {
+        _warnings.push_back(::TerminalApp::SettingsLoadWarnings::InvalidIcon);
+    }
+}
+
 // Method Description:
 // - Create a TerminalSettings object for the provided newTerminalArgs. We'll
 //   use the newTerminalArgs to look up the profile that should be used to

src/cascadia/TerminalApp/CascadiaSettings.h

@@ -115,6 +115,7 @@ private:
     void _ReorderProfilesToMatchUserSettingsOrder();
     void _RemoveHiddenProfiles();
     void _ValidateAllSchemesExist();
+    void _ValidateMediaResources();
 
     friend class TerminalAppLocalTests::SettingsTests;
     friend class TerminalAppLocalTests::ProfileTests;

src/cascadia/TerminalApp/Profile.cpp

@@ -847,6 +847,14 @@ void Profile::SetIconPath(std::wstring_view path)
     _icon.emplace(path);
 }
 
+// Method Description:
+// - Resets the std::optional holding the icon file path string.
+//   HasIcon() will return false after the execution of this function.
+void Profile::ResetIconPath()
+{
+    _icon.reset();
+}
+
 // Method Description:
 // - Returns this profile's icon path, if one is set. Otherwise returns the
 //   empty string. This method will expand any environment variables in the
@@ -880,6 +888,14 @@ winrt::hstring Profile::GetExpandedBackgroundImagePath() const
     return result;
 }
 
+// Method Description:
+// - Resets the std::optional holding the background image file path string.
+//   HasBackgroundImage() will return false after the execution of this function.
+void Profile::ResetBackgroundImagePath()
+{
+    _backgroundImage.reset();
+}
+
 // Method Description:
 // - Returns the name of this profile.
 // Arguments:

src/cascadia/TerminalApp/Profile.h

@@ -89,9 +89,11 @@ public:
     bool HasIcon() const noexcept;
     winrt::hstring GetExpandedIconPath() const;
     void SetIconPath(std::wstring_view path);
+    void ResetIconPath();
 
     bool HasBackgroundImage() const noexcept;
     winrt::hstring GetExpandedBackgroundImagePath() const;
+    void ResetBackgroundImagePath();
 
     CloseOnExitMode GetCloseOnExitMode() const noexcept;
     bool GetSuppressApplicationTitle() const noexcept;

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

@@ -210,4 +210,10 @@ Temporarily using the Windows Terminal default settings.
   <data name="CloseWindowWarningTitle" xml:space="preserve">
     <value>Do you want to close all tabs?</value>
   </data>
+  <data name="InvalidBackgroundImage" xml:space="preserve">
+    <value>Found a profile with an invalid "backgroundImage". Defaulting that profile to have no background image. Make sure that when setting a "backgroundImage", the value is a valid file path to an image.</value>
+  </data>
+  <data name="InvalidIcon" xml:space="preserve">
+    <value>Found a profile with an invalid "icon". Defaulting that profile to have no icon. Make sure that when setting an "icon", the value is a valid file path to an image.</value>
+  </data>
 </root>

src/cascadia/TerminalApp/TerminalWarnings.h

@@ -23,7 +23,9 @@ namespace TerminalApp
     {
         MissingDefaultProfile = 0,
         DuplicateProfile = 1,
-        UnknownColorScheme = 2
+        UnknownColorScheme = 2,
+        InvalidBackgroundImage = 3,
+        InvalidIcon = 4
     };
 
     // SettingsLoadWarnings are scenarios where the settings had invalid state