Use IBM Plex Sans / Lilex (#36084)

The Zed Plex fonts were found to violate the OFL by using the word Plex
in the name.

Lilex has better ligatures and box-drawing characters than Zed Plex
Mono, but Zed Plex Sans should be identical
to IBM Plex Sans.

Closes #15542
Closes zed-industries/zed-fonts#31

Release Notes:

- The "Zed Plex Sans" and "Zed Plex Mono" fonts have been replaced with
"IBM Plex Sans" and "Lilex". The old names still work for backward
compatibility. Other than fixing line-drawing characters, and improving
the ligatures, there should be little visual change as the fonts are all
of the same family.
- Introduced ".ZedSans" and ".ZedMono" as aliases to allow us to easily
change the default fonts in the future. These currently default to "IBM
Plex Sans" and "Lilex" respectively.

crates/gpui/src/platform/linux/text_system.rs

@@ -213,11 +213,7 @@ impl CosmicTextSystemState {
         features: &FontFeatures,
     ) -> Result<SmallVec<[FontId; 4]>> {
         // TODO: Determine the proper system UI font.
-        let name = if name == ".SystemUIFont" {
-            "Zed Plex Sans"
-        } else {
-            name
-        };
+        let name = crate::text_system::font_name_with_fallbacks(name, "IBM Plex Sans");
 
         let families = self
             .font_system

crates/gpui/src/platform/mac/text_system.rs

@@ -211,11 +211,7 @@ impl MacTextSystemState {
         features: &FontFeatures,
         fallbacks: Option<&FontFallbacks>,
     ) -> Result<SmallVec<[FontId; 4]>> {
-        let name = if name == ".SystemUIFont" {
-            ".AppleSystemUIFont"
-        } else {
-            name
-        };
+        let name = crate::text_system::font_name_with_fallbacks(name, ".AppleSystemUIFont");
 
         let mut font_ids = SmallVec::new();
         let family = self

crates/gpui/src/platform/windows/direct_write.rs

@@ -498,8 +498,9 @@ impl DirectWriteState {
                 )
                 .unwrap()
             } else {
+                let family = self.system_ui_font_name.clone();
                 self.find_font_id(
-                    target_font.family.as_ref(),
+                    font_name_with_fallbacks(target_font.family.as_ref(), family.as_ref()),
                     target_font.weight,
                     target_font.style,
                     &target_font.features,
@@ -512,7 +513,6 @@ impl DirectWriteState {
                     }
                     #[cfg(not(any(test, feature = "test-support")))]
                     {
-                        let family = self.system_ui_font_name.clone();
                         log::error!("{} not found, use {} instead.", target_font.family, family);
                         self.get_font_id_from_font_collection(
                             family.as_ref(),

crates/gpui/src/text_system.rs

@@ -65,7 +65,7 @@ impl TextSystem {
             font_runs_pool: Mutex::default(),
             fallback_font_stack: smallvec![
                 // TODO: Remove this when Linux have implemented setting fallbacks.
-                font("Zed Plex Mono"),
+                font(".ZedMono"),
                 font("Helvetica"),
                 font("Segoe UI"),  // Windows
                 font("Cantarell"), // Gnome
@@ -96,7 +96,7 @@ impl TextSystem {
     }
 
     /// Get the FontId for the configure font family and style.
-    pub fn font_id(&self, font: &Font) -> Result<FontId> {
+    fn font_id(&self, font: &Font) -> Result<FontId> {
         fn clone_font_id_result(font_id: &Result<FontId>) -> Result<FontId> {
             match font_id {
                 Ok(font_id) => Ok(*font_id),
@@ -844,3 +844,16 @@ impl FontMetrics {
         (self.bounding_box / self.units_per_em as f32 * font_size.0).map(px)
     }
 }
+
+#[allow(unused)]
+pub(crate) fn font_name_with_fallbacks<'a>(name: &'a str, system: &'a str) -> &'a str {
+    // Note: the "Zed Plex" fonts were deprecated as we are not allowed to use "Plex"
+    // in a derived font name. They are essentially indistinguishable from IBM Plex/Lilex,
+    // and so retained here for backward compatibility.
+    match name {
+        ".SystemUIFont" => system,
+        ".ZedSans" | "Zed Plex Sans" => "IBM Plex Sans",
+        ".ZedMono" | "Zed Plex Mono" => "Lilex",
+        _ => name,
+    }
+}

crates/gpui/src/text_system/line_wrapper.rs

@@ -327,7 +327,7 @@ mod tests {
     fn build_wrapper() -> LineWrapper {
         let dispatcher = TestDispatcher::new(StdRng::seed_from_u64(0));
         let cx = TestAppContext::build(dispatcher, None);
-        let id = cx.text_system().font_id(&font("Zed Plex Mono")).unwrap();
+        let id = cx.text_system().resolve_font(&font(".ZedMono"));
         LineWrapper::new(id, px(16.), cx.text_system().platform_text_system.clone())
     }