IJPL-187512 [terminal] Implement font fallback

Because some fonts are missing some characters
used in popular shell themes, we need to have
a fallback font.

Since a fallback font can only be provided to the editor
through the FontPreferences API, we can't use
TerminalFontSettings directly anymore.
Still, we need it for TerminalOptionsConfigurable
because using FontPreferences there would be messy.

TerminalFontSettingsService already inherits
getFontPreferences from AppFontOptions,
but it only has a fallback family if it's not null
when the state is loaded (see copyState).
But we need it to be always available
except when it's not specified at all AND
the main font is also the default one.

Therefore, we override getFontPreferences
to ensure that a fallback is always provided
if necessary.

(cherry picked from commit 905fe55100ea8358fd9bea7679ccff84629da996)

IJ-CR-162755

GitOrigin-RevId: 77941a16d8c54e6cebd90cda1fe80b5bfe300570

plugins/terminal/resources/messages/TerminalBundle.properties

@@ -85,6 +85,7 @@ settings.environment.variables=&Environment variables:
 settings.shell.path=&Shell path:
 settings.tab.name=Default &tab name:
 settings.font.name=&Font:
+settings.fallback.font.name=Fallback:
 settings.font.size=Size:
 settings.line.height=Line height:
 settings.column.width=Column width:

plugins/terminal/src/org/jetbrains/plugins/terminal/TerminalFontSettingsService.kt

@@ -49,6 +49,7 @@ class TerminalFontSettingsService : AppFontOptions<TerminalFontSettingsState>()
     val preferences = fontPreferences
     return TerminalFontSettings(
       fontFamily = preferences.fontFamily,
+      fallbackFontFamily = preferences.effectiveFontFamilies.getOrNull(1) ?: FontPreferences.DEFAULT_FONT_NAME,
       fontSize = TerminalFontSize.ofFloat(preferences.getSize2D(preferences.fontFamily)),
       lineSpacing = TerminalLineSpacing.ofFloat(preferences.lineSpacing),
       columnSpacing = columnSpacing,
@@ -73,6 +74,10 @@ class TerminalFontSettingsService : AppFontOptions<TerminalFontSettingsState>()
     val boldSubFamily = FontFamilyService.getRecommendedBoldSubFamily(settings.fontFamily, regularSubFamily)
     newPreferences.boldSubFamily = boldSubFamily
     newPreferences.setFontSize(settings.fontFamily, settings.fontSize.floatValue)
+    if (settings.fallbackFontFamily != settings.fontFamily) {
+      newPreferences.addFontFamily(settings.fallbackFontFamily)
+      newPreferences.setFontSize(settings.fallbackFontFamily, settings.fontSize.floatValue)
+    }
     newPreferences.lineSpacing = settings.lineSpacing.floatValue
     // then apply the settings that aren't a part of FontPreferences
     columnSpacing = settings.columnSpacing
@@ -84,6 +89,16 @@ class TerminalFontSettingsService : AppFontOptions<TerminalFontSettingsState>()
     }
   }
 
+  override fun getFontPreferences(): FontPreferences {
+    val result = super.getFontPreferences()
+    // The default fallback family isn't serialized, but we need to explicitly add it anyway if we're not using the default font.
+    // Otherwise, if the explicitly set font is missing some characters, the default font won't be used as a fallback.
+    if (result.effectiveFontFamilies.size == 1 && result.fontFamily != FontPreferences.DEFAULT_FONT_NAME) {
+      (result as FontPreferencesImpl).register(FontPreferences.DEFAULT_FONT_NAME, result.getSize2D(result.fontFamily))
+    }
+    return result
+  }
+
   override fun createFontState(fontPreferences: FontPreferences): TerminalFontSettingsState =
     TerminalFontSettingsState(fontPreferences).also {
       it.COLUMN_SPACING = columnSpacing.floatValue
@@ -272,6 +287,7 @@ interface TerminalFontSettingsListener {
 
 internal data class TerminalFontSettings(
   val fontFamily: String,
+  val fallbackFontFamily: String,
   val fontSize: TerminalFontSize,
   val lineSpacing: TerminalLineSpacing,
   val columnSpacing: TerminalColumnSpacing,
@@ -282,6 +298,7 @@ class TerminalFontSettingsState: AppEditorFontOptions.PersistentFontPreferences
   @Suppress("unused") // for serialization
   constructor(): super() {
     LINE_SPACING = DEFAULT_TERMINAL_LINE_SPACING.floatValue // to ensure that values different from OUR default are saved
+    SECONDARY_FONT_FAMILY = FontPreferences.DEFAULT_FONT_NAME
   }
 
   constructor(fontPreferences: FontPreferences): super(fontPreferences)

plugins/terminal/src/org/jetbrains/plugins/terminal/TerminalOptionsConfigurable.kt

@@ -150,6 +150,16 @@ internal class TerminalOptionsConfigurable(private val project: Project) : Bound
                 setter = { fontSettings = fontSettings.copy(fontFamily = it) },
               ).toNullableProperty()
             )
+          cell(fontComboBox())
+            .label(message("settings.fallback.font.name"))
+            .bind(
+              componentGet = { comboBox -> comboBox.fontName },
+              componentSet = {comboBox, value -> comboBox.fontName = value },
+              MutableProperty(
+                getter = { fontSettings.fallbackFontFamily },
+                setter = { fontSettings = fontSettings.copy(fallbackFontFamily = it) },
+              ).toNullableProperty()
+            )
         }
 
         row {

plugins/terminal/src/org/jetbrains/plugins/terminal/block/ui/TerminalUiUtils.kt

@@ -56,6 +56,7 @@ import com.jediterm.terminal.ui.AwtTransformers
 import com.jediterm.terminal.util.CharUtils
 import org.intellij.lang.annotations.MagicConstant
 import org.jetbrains.annotations.ApiStatus
+import org.jetbrains.plugins.terminal.TerminalFontSettingsService
 import org.jetbrains.plugins.terminal.block.output.TextAttributesProvider
 import org.jetbrains.plugins.terminal.block.output.TextStyleAdapter
 import org.jetbrains.plugins.terminal.block.session.TerminalModel
@@ -294,9 +295,7 @@ object TerminalUiUtils {
 
 fun EditorImpl.applyFontSettings(newSettings: JBTerminalSystemSettingsProviderBase) {
   colorsScheme.apply {
-    editorFontName = newSettings.terminalFont.fontName
-    setEditorFontSize(newSettings.terminalFont.size2D)
-    lineSpacing = newSettings.lineSpacing
+    fontPreferences = newSettings.fontPreferences
   }
   settings.apply {
     characterGridWidthMultiplier = newSettings.columnSpacing