katex [nfc]: Handle error immediately on spanClasses overrun

Like an early return, this (a) brings the consequence of the error
immediately next to the condition defining it, and (b) lets the normal
happy case continue vertically down without adding indentation.

Author: gnprice

lib/model/katex.dart

@@ -278,73 +278,62 @@ class _KatexParser {
         case 'fontsize-ensurer':
           // .sizing,
           // .fontsize-ensurer { ... }
-          if (index + 1 < spanClasses.length) {
-            final resetSizeClass = spanClasses[index++];
-            final sizeClass = spanClasses[index++];
+          if (index + 2 > spanClasses.length) throw KatexHtmlParseError();
+          final resetSizeClass = spanClasses[index++];
+          final sizeClass = spanClasses[index++];
 
-            final resetSizeClassSuffix = _resetSizeClassRegExp.firstMatch(resetSizeClass)?.group(1);
-            final sizeClassSuffix = _sizeClassRegExp.firstMatch(sizeClass)?.group(1);
+          final resetSizeClassSuffix = _resetSizeClassRegExp.firstMatch(resetSizeClass)?.group(1);
+          final sizeClassSuffix = _sizeClassRegExp.firstMatch(sizeClass)?.group(1);
 
-            if (resetSizeClassSuffix != null && sizeClassSuffix != null) {
-              const sizes = <double>[0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.44, 1.728, 2.074, 2.488];
+          if (resetSizeClassSuffix != null && sizeClassSuffix != null) {
+            const sizes = <double>[0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.44, 1.728, 2.074, 2.488];
 
-              final resetSizeIdx = int.parse(resetSizeClassSuffix, radix: 10);
-              final sizeIdx = int.parse(sizeClassSuffix, radix: 10);
+            final resetSizeIdx = int.parse(resetSizeClassSuffix, radix: 10);
+            final sizeIdx = int.parse(sizeClassSuffix, radix: 10);
 
-              // These indexes start at 1.
-              if (resetSizeIdx <= sizes.length && sizeIdx <= sizes.length) {
-                styles.fontSizeEm = sizes[sizeIdx - 1] / sizes[resetSizeIdx - 1];
-                continue;
-              }
+            // These indexes start at 1.
+            if (resetSizeIdx <= sizes.length && sizeIdx <= sizes.length) {
+              styles.fontSizeEm = sizes[sizeIdx - 1] / sizes[resetSizeIdx - 1];
+              continue;
             }
           }
 
           throw KatexHtmlParseError();
 
         case 'delimsizing':
           // .delimsizing { ... }
-          if (index < spanClasses.length) {
-            final nextClass = spanClasses[index++];
-            switch (nextClass) {
-              case 'size1':
-                styles.fontFamily = 'KaTeX_Size1';
-              case 'size2':
-                styles.fontFamily = 'KaTeX_Size2';
-              case 'size3':
-                styles.fontFamily = 'KaTeX_Size3';
-              case 'size4':
-                styles.fontFamily = 'KaTeX_Size4';
-
-              case 'mult':
-                // TODO handle nested spans with `.delim-size{1,4}` class.
-                break;
-            }
-
-            if (styles.fontFamily == null) throw KatexHtmlParseError();
-
-            continue;
+          if (index + 1 > spanClasses.length) throw KatexHtmlParseError();
+          final nextClass = spanClasses[index++];
+          switch (nextClass) {
+            case 'size1':
+              styles.fontFamily = 'KaTeX_Size1';
+            case 'size2':
+              styles.fontFamily = 'KaTeX_Size2';
+            case 'size3':
+              styles.fontFamily = 'KaTeX_Size3';
+            case 'size4':
+              styles.fontFamily = 'KaTeX_Size4';
+
+            case 'mult':
+              // TODO handle nested spans with `.delim-size{1,4}` class.
+              break;
           }
 
-          throw KatexHtmlParseError();
+          if (styles.fontFamily == null) throw KatexHtmlParseError();
 
         // TODO handle .nulldelimiter and .delimcenter .
 
         case 'op-symbol':
           // .op-symbol { ... }
-          if (index < spanClasses.length) {
-           final nextClass = spanClasses[index++];
-            switch (nextClass) {
-              case 'small-op':
-                styles.fontFamily = 'KaTeX_Size1';
-              case 'large-op':
-                styles.fontFamily = 'KaTeX_Size2';
-            }
-            if (styles.fontFamily == null) throw KatexHtmlParseError();
-
-            continue;
+          if (index + 1 > spanClasses.length) throw KatexHtmlParseError();
+          final nextClass = spanClasses[index++];
+          switch (nextClass) {
+            case 'small-op':
+              styles.fontFamily = 'KaTeX_Size1';
+            case 'large-op':
+              styles.fontFamily = 'KaTeX_Size2';
           }
-
-          throw KatexHtmlParseError();
+          if (styles.fontFamily == null) throw KatexHtmlParseError();
 
         // TODO handle more classes from katex.scss