[system_fonts] Add Helvetica/.SFUIText to load list.

Should fix OS X (or is it called macOS now?)

Related to #220

src/system_fonts.rs

@@ -1,10 +1,10 @@
 use lazy_static::lazy_static;
 
-use crate::constants::CONSOLE_FONTS;
+//use crate::constants::CONSOLE_FONTS;
 
 use font_kit::{
     family_name::FamilyName as FKFamilyName, handle::Handle as FKHandle, properties::Properties,
-    source::SystemSource,
+    source::SystemSource, error::SelectionError::NotFound as FKNotFoundError,
 };
 
 use std::fs;
@@ -18,28 +18,62 @@ pub struct Font {
 
 fn load_font(family: &[FKFamilyName]) -> Font {
     log::debug!("Looking for a UI font to satisfy request for {:?}", family);
-    let font = match SystemSource::new().select_best_match(family, &Properties::new()) {
-        Ok(FKHandle::Path { path, .. }) => Font {
-            path: Some(path.clone()),
-            data: fs::read(path).expect("Failed to open font path system specified"),
+    let mut font = None;
+    let source = SystemSource::new();
+    let props = Properties::new();
+    for fkfamname in family {
+        let best_match = source.select_best_match(&[fkfamname.clone()], &props);
+        if let Err(FKNotFoundError) = best_match {
+            log::debug!("Skipped {:?}", fkfamname);
+        }
+        font = match best_match {
+            Ok(FKHandle::Path { path, .. }) => Some(Font {
+                path: Some(path.clone()),
+                data: fs::read(path).expect("Failed to open font path system specified"),
+            }),
+            Ok(FKHandle::Memory { bytes, .. }) => Some(Font {
+                path: None,
+                data: Arc::try_unwrap(bytes).expect("Failed to load in-memory font"),
+            }),
+            // try next font…
+            Err(FKNotFoundError) => {continue}
+            Err(e) => panic!(
+                "Failed to select font for {:?} ! Error from fontkit {:?}",
+                family, e
+            ),
+        };
+        if let Some(ref font) = font {
+            log::debug!("OK: Found {:?} (matched @ {:?}, len {})", &font.path, fkfamname, font.data.len());
+            break
+        }
+    }
+    match font {
+        Some(font) => {
+            font
         },
-        Ok(FKHandle::Memory { bytes, .. }) => Font {
-            path: None,
-            data: Arc::try_unwrap(bytes).expect("Failed to load in-memory font"),
-        },
-        Err(e) => panic!(
-            "Failed to select font for {:?} ! Error from fontkit {:?}",
-            family, e
-        ),
-    };
-    log::debug!("OK: Found {:?} (len {})", &font.path, font.data.len());
-    font
+        None => {
+            panic!("In request for {:?}, no matches were made; cannot render UI!", family);
+        }
+    }
 }
 
 lazy_static! {
+    /// Windows 10 comes first because if we allow Windows to match on `sans-serif`, it will give
+    /// us Verdana, which looks incongruent on modern Windows OS. So, we specifically ask for Segoe
+    /// UI first. Meanwhile, on macOS…the situation is very confusing and complex due to Apple's
+    /// difficulty in deciding on a default font. I believe it works to try "Helvetica" and then
+    /// ".SFUI-Text" (San Francisco UI Text); Apple does _NOT_ resolve `sans-serif` to anything,
+    /// resulting in crash which became issue №220.
     pub static ref SYSTEMSANS: Font = load_font(&[
+        // Windows 10
         FKFamilyName::Title("Segoe UI".to_string()),
-        FKFamilyName::SansSerif
+        // Linux (fontconfig)
+        FKFamilyName::SansSerif,
+        // macOS ??
+        FKFamilyName::Title("Helvetica".to_string()),
+        // macOS ??
+        FKFamilyName::Title(".SFUIText".to_string()),
     ]);
-    pub static ref SYSTEMMONO: Font = load_font(CONSOLE_FONTS.as_slice());
+    //TODO: Replace console.
+    //pub static ref SYSTEMMONO: Font = load_font(CONSOLE_FONTS.as_slice());
 }