Fix CJK fonts again and misc. font issues (#14575)

* Push system-ui further down the stack, fix #12966

* Fix Firefox showing U+300x in emoji font and more

* Revert emoji font and fix long-standing Safari bug

* Exclude Safari emoji fix above 1.25x zoom

* Minor correctness/typo fix, affects only legacy platforms

* Emoji consistency for monospace (e.g. EasyMDE)

* Override paradigm; macOS/iOS-specific metric fix

* Move whitespace fix to font-face

* Handle metric calculation errors with Firefox

* One last workaround for aliased fonts in Linux

3 files changed, 159 insertions, 38 deletions

diff --git a/web_src/less/_base.less b/web_src/less/_base.less
index 351dbf5da0..121a2b2064 100644
--- a/web_src/less/_base.less
+++ b/web_src/less/_base.less
@@ -1,10 +1,9 @@
 :root {
   /* documented customizable variables */
-  --fonts-proportional: system-ui, -apple-system, "BlinkMacSystemFont", "Segoe UI", "Roboto", "Helvetica Neue", "Arial", "Noto Sans", "Liberation Sans", sans-serif;
-  --fonts-monospace: "SFMono-Regular", "Menlo", "Monaco", "Consolas", "Liberation Mono", "Courier New", monospace;
-  --fonts-emoji: "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji", "Twemoji Mozilla";
+  --fonts-proportional: -apple-system, "Segoe UI", system-ui, "Roboto", "Helvetica Neue", "Arial";
+  --fonts-monospace: "SFMono-Regular", "Menlo", "Monaco", "Consolas", "Liberation Mono", "Courier New", monospace, var(--fonts-emoji);
+  --fonts-emoji: "Apple Color Emoji", "Segoe UI Emoji", "Noto Color Emoji", "Twemoji Mozilla";
   /* other variables */
-  --fonts-regular: var(--fonts-proportional), var(--fonts-emoji);
   --border-radius: .28571429rem;
   --opacity-disabled: .55;
   --color-primary: #4183c4;
@@ -115,36 +114,8 @@
   --checkbox-mask-indeterminate: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" width="16" height="16"><path fill-rule="evenodd" d="M2 7.75A.75.75 0 012.75 7h10a.75.75 0 010 1.5h-10A.75.75 0 012 7.75z"></path></svg>');
 }
 
-:root:lang(ja) {
-  --fonts-proportional: "Hiragino Kaku Gothic ProN", "Yu Gothic", "Source Han Sans JP", "Noto Sans CJK JP", "Droid Sans Japanese", "Meiryo", "MS PGothic";
-}
-
-:root:lang(zh-CN) {
-  --fonts-proportional: "PingFang SC", "Hiragino Sans GB", "Source Han Sans CN", "Source Han Sans SC", "Noto Sans CJK SC", "Microsoft YaHei", "Heiti SC", "SimHei";
-}
-
-:root:lang(zh-TW) {
-  --fonts-proportional: "PingFang TC", "Hiragino Sans TC", "Source Han Sans TW", "Source Han Sans TC", "Noto Sans CJK TC", "Microsoft JhengHei", "Heiti TC", "PMingLiU";
-}
-
-:root:lang(zh-HK) {
-  --fonts-proportional: "PingFang HK", "Hiragino Sans TC", "Source Han Sans HK", "Source Han Sans TC", "Noto Sans CJK TC", "Microsoft JhengHei", "Heiti TC", "PMingLiU_HKSCS", "PMingLiU";
-}
-
-:root:lang(ko) {
-  --fonts-proportional: "Apple SD Gothic Neo", "NanumBarunGothic", "Malgun Gothic", "Gulim", "Dotum", "Nanum Gothic", "Source Han Sans KR", "Noto Sans CJK KR";
-}
-
-@font-face {
-  font-family: "Yu Gothic";
-  src: local("Yu Gothic Medium");
-  font-weight: 400;
-}
-
-@font-face {
-  font-family: "Yu Gothic";
-  src: local("Yu Gothic Bold");
-  font-weight: 500;
+:root * {
+  --fonts-regular: var(--fonts-override, var(--fonts-proportional)), "Noto Sans", "Liberation Sans", var(--fonts-emoji), sans-serif;
 }
 
 textarea {
@@ -1151,10 +1122,18 @@ footer {
     }
   }
 
-  .ui.language .menu {
-    max-height: 500px;
-    overflow-y: auto;
-    margin-bottom: 7px;
+  .ui.language {
+    .menu {
+      max-height: 500px;
+      overflow-y: auto;
+      margin-bottom: 7px;
+    }
+
+    .svg {
+      margin-right: .15em;
+      vertical-align: top;
+      margin-top: calc(2em - 16px);
+    }
   }
 
   .ui {
@@ -1885,6 +1864,17 @@ table th[data-sortt-desc] {
   font-style: normal !important;
   font-weight: normal !important;
   vertical-align: -.075em;
+
+  @supports (-webkit-hyphens:none) {
+    body:not(.safari-above125) & {
+      font-size: inherit;
+      vertical-align: inherit;
+      img {
+        font-size: 1.25em;
+        vertical-align: -.225em !important;
+      }
+    }
+  }
 }
 
 .emoji img,
diff --git a/web_src/less/_font_i18n.less b/web_src/less/_font_i18n.less
new file mode 100644
index 0000000000..f92459b6fd
--- /dev/null
+++ b/web_src/less/_font_i18n.less
@@ -0,0 +1,130 @@
+/* font i18n */
+:root {
+  /* customizable localized variables */
+  :lang(ja) {
+    --fonts-override: var(--fonts-default-override-ja);
+  }
+  :lang(zh-CN) {
+    --fonts-override: var(--fonts-default-override-zh-cn);
+  }
+  :lang(zh-TW) {
+    --fonts-override: var(--fonts-default-override-zh-tw);
+  }
+  :lang(zh-HK) {
+    --fonts-override: var(--fonts-default-override-zh-hk);
+  }
+  :lang(ko) {
+    --fonts-override: var(--fonts-default-override-ko);
+  }
+}
+
+[lang] {
+  font-family: var(--fonts-regular);
+}
+
+each(@fonts, {
+  @weights: .gen-weights-all(@value);
+  @locale: replace(@key, "@", "-");
+  .font-face-cjk(~"system-ui@{locale}", @weights[@light], 300);
+  .font-face-cjk(~"system-ui@{locale}", @weights[@regular], 400);
+  .font-face-cjk(~"system-ui@{locale}", @weights[@medium], 500);
+  .font-face-cjk(~"system-ui@{locale}", @weights[@bold], 700);
+  /* Safari on macOS/iOS */
+  @font-face {
+    font-family: ~"system-ui@{locale}";
+    src: local("HelveticaNeue");
+    unicode-range: U+A0;
+  }
+  /* Other browsers on macOS/iOS */
+  @supports not (-webkit-hyphens:none) {
+    @font-face {
+      font-family: ~"system-ui@{locale}";
+      src: local("HelveticaNeue");
+      unicode-range: U+20;
+    }
+  }
+  :root {
+    /* Special handling for Firefox on Windows/Linux */
+    @supports (-moz-appearance:none) {
+      --fonts-default-override@{locale}: ~"var(--fonts-proportional), system-ui@{locale}";
+    }
+    --fonts-default-override@{locale}: ~"system-ui@{locale}, var(--fonts-proportional)";
+  }
+});
+
+@fonts: {
+  @ja:
+    "HiraginoSans-:{W2,W4,W5,W6}", "HiraKakuProN-:{W3,W6}", "Hiragino Kaku Gothic ProN :{W3,W6}",
+    .shs("JP")[], .shs("J")[], .noto("JP")[], .shs("")[],
+    /* https://acetaminophen.hatenablog.com/entry/2016/02/15/225009 */
+    "Yu Gothic :{Regular,Medium,Bold}", "YuGothic :{Regular,Medium,Bold}",
+    "Droid Sans Japanese:{}", "Meiryo:{, Bold}", "MS PGothic:{}";
+  @zh-cn:
+    .pingfang("SC")[],
+    .shs("CN")[], .shs("SC")[], .noto("SC")[],
+    "HiraginoSansGB-:{W3,W6}", "Hiragino Sans GB :{W3,W6}",
+    "Microsoft YaHei:{ Light,, Bold}", "Heiti SC :{Light,Medium}", "SimHei:{}";
+  @zh-tw:
+    .pingfang("TC")[],
+    .shs("TW")[], .shs("TC")[], .noto("TC")[],
+    "HiraginoSansTC-:{W3,W6}", "Hiragino Sans TC :{W3,W6}",
+    "Microsoft JhengHei:{ Light,, Bold}", "Heiti TC :{Light,Medium}", "PMingLiU:{}";
+  @zh-hk:
+    .pingfang("HK")[],
+    .shs("HK")[], .shs("HC")[], .noto("HK")[], .shs("TC")[], .noto("TC")[],
+    "HiraginoSansTC-:{W3,W6}", "Hiragino Sans TC :{W3,W6}",
+    "Microsoft JhengHei:{ Light,, Bold}", "Heiti TC :{Light,Medium}", "PMingLiU_HKSCS:{}", "PMingLiU:{}";
+  @ko:
+    "AppleSDGothicNeo-:{Light,Regular,Medium,SemiBold}",
+    .shs("KR")[], .shs("K")[], .noto("KR")[],
+    "NanumBarunGothic:{ Light,, Bold}",
+    "Malgun Gothic:{ Semilight,, Bold}", "Nanum Gothic:{, Bold}", "Dotum:{}";
+}
+
+.noto(@suffix) { @value: "Noto Sans CJK @{suffix} ", "NotoSansCJK@{suffix}-"; }
+.shs(@suffix) { @value: replace("Source Han Sans @{suffix} ", "  ", " "), "SourceHanSans@{suffix}-"; }
+.pingfang(@suffix) { @value: "PingFang@{suffix}-:{Light,Regular,Medium,Semibold}"; }
+.font-face-cjk(@family, @src, @weight) {
+  @font-face {
+    font-family: @family;
+    src: @src;
+    font-weight: @weight;
+    unicode-range: ~"U+11??, U+2E80-4DBF, U+4E00-9FFF, U+A960-A97F, U+AC00-D7FF, U+F900-FAFF, U+FE00-FE6F, U+FF00-FFEF, U+1F2??, U+2????";
+  }
+}
+
+.gen-weights(@family) when (isstring(@family)) {
+  @family-str: replace(@family, ":\{.*\}$", "");
+  // apply standard style names if none is given
+  // should the font have no styles, use :{}, as in "SimHei:{}"
+  @weights-str: if(@family = @family-str, "Light,Regular,Medium,Bold", replace(@family, ".*:\{(.*)\}$", "$1"));
+  @lightest: replace(@weights-str, ",.*", "");
+  @boldest: replace(@weights-str, ".*,", "");
+  @2ndboldest: replace(@weights-str, "(?:.*,|)([^,]*),.*$", "$1");
+  @2ndlightest: if(@2ndboldest = @lightest, @lightest, replace(@weights-str, "^.*?,([^,]*).*", "$1"));
+
+  @light: local("@{family-str}@{lightest}");
+  @regular: local("@{family-str}@{2ndlightest}");
+  @medium: local("@{family-str}@{2ndboldest}");
+  @bold: local("@{family-str}@{boldest}");
+}
+.gen-weights(@family) when not (isstring(@family)) {
+  .gen-weights-all(@family);
+}
+.gen-weights(@family, @last) {
+  @this: .gen-weights(@family);
+
+  @light: @last[@light], @this[@light];
+  @regular: @last[@regular], @this[@regular];
+  @medium: @last[@medium], @this[@medium];
+  @bold: @last[@bold], @this[@bold];
+}
+.gen-weights-all(@family) when not (isstring(@family)) {
+  .gen-weights-all(@family, length(@family));
+}
+.gen-weights-all(@family, 1) when not (isstring(@family)) {
+  .gen-weights(extract(@family, 1));
+}
+.gen-weights-all(@family, @ctr) when not (isstring(@family)) and (@ctr > 1) and (@ctr <= length(@family)) {
+  .gen-weights(extract(@family, @ctr), .gen-weights-all(@family, @ctr - 1));
+}
diff --git a/web_src/less/index.less b/web_src/less/index.less
index cd70eedefd..b3cbf8abb7 100644
--- a/web_src/less/index.less
+++ b/web_src/less/index.less
@@ -13,6 +13,7 @@
 
 @import "_svg";
 @import "_tribute";
+@import "_font_i18n";
 @import "_base";
 @import "_markdown";
 @import "_home";