I think this is pretty close, but we're gonna wait on this one

fixes #6160

  [3:12 PM] Dustin Howett
    > we're gonna have to reason about what happens when we start keeping disconnected leaves (for user settings purposes)
    >
    > like, they will exist and they can be the default profile but we need a sane fallback
    >
    > and that will help us detect that there was a source but no generata

  So I'm stashing this until later after the elements of #9997 merge

src/cascadia/TerminalApp/AppLogic.cpp

@@ -49,6 +49,7 @@ static const std::array<std::wstring_view, static_cast<uint32_t>(SettingsLoadWar
     USES_RESOURCE(L"InvalidSplitSize"),
     USES_RESOURCE(L"FailedToParseStartupActions"),
     USES_RESOURCE(L"FailedToParseSubCommands"),
+    USES_RESOURCE(L"DidNotFindDynamicDefaultProfile"),
 };
 static const std::array<std::wstring_view, static_cast<uint32_t>(SettingsLoadErrors::ERRORS_SIZE)> settingsLoadErrorsLabels {
     USES_RESOURCE(L"NoProfilesText"),
@@ -488,6 +489,22 @@ namespace winrt::TerminalApp::implementation
 
                     warningsTextBlock.Inlines().Append(legacyGlobalsLink);
                 }
+                else if (warning == SettingsLoadWarnings::DidNotFindDynamicDefaultProfile)
+                {
+                    // Add the URL here too
+                    const auto linkLabel = RS_(L"DynamicDefaultProfileHrefLabel");
+                    const auto uriValue = RS_(L"DynamicDefaultProfileHrefUrl");
+
+                    winrt::Windows::UI::Xaml::Documents::Run legacyGlobalsLinkText;
+                    winrt::Windows::UI::Xaml::Documents::Hyperlink legacyGlobalsLink;
+                    winrt::Windows::Foundation::Uri linkUri{ uriValue };
+
+                    legacyGlobalsLinkText.Text(linkLabel);
+                    legacyGlobalsLink.NavigateUri(linkUri);
+                    legacyGlobalsLink.Inlines().Append(legacyGlobalsLinkText);
+
+                    warningsTextBlock.Inlines().Append(legacyGlobalsLink);
+                }
 
                 warningsTextBlock.Inlines().Append(Documents::LineBreak{});
             }

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

@@ -232,6 +232,18 @@
   <data name="FailedToParseSubCommands" xml:space="preserve">
     <value>&#x2022; Failed to parse all subcommands of nested command.</value>
   </data>
+  <data name="DidNotFindDynamicDefaultProfile" xml:space="preserve">
+    <value>&#x2022; We detected your default profile is a dynamic profile that did not generate. The original source of this profile may no longer exist.
+    </value>
+    <comment>{Locked="&#x2022;"} This glyph is a bullet, used in a bulleted list.</comment>
+  </data>
+  <data name="DynamicDefaultProfileHrefUrl" xml:space="preserve">
+    <value>https://go.microsoft.com/fwlink/?linkid=2170601</value>
+    <comment>{Locked}This is a FWLink, so it will be localized with the fwlink tool</comment>
+  </data>
+  <data name="DynamicDefaultProfileHrefLabel" xml:space="preserve">
+    <value>For more info, see this web page.</value>
+  </data>
   <data name="MissingRequiredParameter" xml:space="preserve">
     <value>&#x2022; Found a keybinding that was missing a required parameter value. This keybinding will be ignored.</value>
     <comment>{Locked="&#x2022;"} This glyph is a bullet, used in a bulleted list.</comment>

src/cascadia/TerminalSettingsModel/CascadiaSettings.cpp

@@ -532,6 +532,7 @@ void CascadiaSettings::_ValidateDefaultProfileExists()
 
     if (nullDefaultProfile || defaultProfileNotInProfiles)
     {
+        // TODO! Don't add the warning if we already have a DidNotFindDynamicDefaultProfile warning.
         _warnings.Append(Microsoft::Terminal::Settings::Model::SettingsLoadWarnings::MissingDefaultProfile);
         // Use the first profile as the new default
 

src/cascadia/TerminalSettingsModel/CascadiaSettingsSerialization.cpp

@@ -942,6 +942,31 @@ void CascadiaSettings::_LayerOrCreateProfile(const Json::Value& profileJson)
             profile->LayerJson(profileJson);
             _allProfiles.Append(*profile);
         }
+        else
+        {
+            // TODO!
+            const auto guid = Profile::GetGuidOrGenerateForJson(profileJson);
+            try
+            {
+                // This might throw
+                if (guid == _globals->DefaultProfile())
+                {
+                    _warnings.Append(SettingsLoadWarnings::DidNotFindDynamicDefaultProfile);
+                }
+            }
+            catch (...)
+            {
+                // if it did, then the DefaultProfile isn't valid. It might be the name of the profile!
+                if (GlobalSettings().HasUnparsedDefaultProfile())
+                {
+                    const auto unparsedDefaultProfile{ GlobalSettings().UnparsedDefaultProfile() };
+                    if (Profile::GetNameForJson(profileJson) == unparsedDefaultProfile)
+                    {
+                        _warnings.Append(SettingsLoadWarnings::DidNotFindDynamicDefaultProfile);
+                    }
+                }
+            }
+        }
     }
 
     if (profile && _userDefaultProfileSettings)

src/cascadia/TerminalSettingsModel/Profile.cpp

@@ -516,6 +516,11 @@ winrt::guid Profile::GetGuidOrGenerateForJson(const Json::Value& json) noexcept
     return Profile::_GenerateGuidForProfile(name, source);
 }
 
+winrt::hstring Profile::GetNameForJson(const Json::Value& json) noexcept
+{
+    return JsonUtils::GetValueForKey<hstring>(json, NameKey);
+}
+
 // Method Description:
 // - Create a new serialized JsonObject from an instance of this class
 // Arguments:

src/cascadia/TerminalSettingsModel/Profile.h

@@ -100,6 +100,7 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
 
         hstring EvaluatedStartingDirectory() const;
         static guid GetGuidOrGenerateForJson(const Json::Value& json) noexcept;
+        static hstring GetNameForJson(const Json::Value& json) noexcept;
 
         Model::IAppearanceConfig DefaultAppearance();
         Model::FontConfig FontInfo();

src/cascadia/TerminalSettingsModel/TerminalWarnings.idl

@@ -22,6 +22,7 @@ namespace Microsoft.Terminal.Settings.Model
         InvalidSplitSize = 12,
         FailedToParseStartupActions = 13,
         FailedToParseSubCommands = 14,
+        DidNotFindDynamicDefaultProfile = 15,
         WARNINGS_SIZE // IMPORTANT: This MUST be the last value in this enum. It's an unused placeholder.
     };