build: tslint rule to enforce html tags escaping in comments

tools/tslint-rules/noUnescapedHtmlTagRule.ts

@@ -0,0 +1,64 @@
+import * as ts from 'typescript';
+import * as Lint from 'tslint';
+import * as utils from 'tsutils';
+
+const ERROR_MESSAGE =
+  'An HTML tag delimiter (< or >) may only appear in a JSDoc comment if it is escaped.' +
+  ' This prevents failures in document generation caused by a misinterpreted tag.';
+
+/**
+ * Rule that walks through all comments inside of the library and adds failures when it
+ * detects unescaped HTML tags inside of multi-line comments.
+ */
+export class Rule extends Lint.Rules.AbstractRule {
+
+  apply(sourceFile: ts.SourceFile) {
+    return this.applyWithWalker(new NoUnescapedHtmlTagWalker(sourceFile, this.getOptions()));
+  }
+}
+
+class NoUnescapedHtmlTagWalker extends Lint.RuleWalker {
+
+  visitSourceFile(sourceFile: ts.SourceFile) {
+    utils.forEachComment(sourceFile, (fullText, commentRange) => {
+      const htmlIsEscaped =
+        this._parseForHtml(fullText.substring(commentRange.pos, commentRange.end));
+      if (commentRange.kind === ts.SyntaxKind.MultiLineCommentTrivia && !htmlIsEscaped) {
+        this.addFailureAt(commentRange.pos, commentRange.end - commentRange.pos, ERROR_MESSAGE);
+      }
+    });
+
+    super.visitSourceFile(sourceFile);
+  }
+
+  /** Gets whether the comment's HTML, if any, is properly escaped */
+  private _parseForHtml(fullText: string): boolean {
+    const matches = /[<>]/;
+    const backtickCount = fullText.split('`').length - 1;
+
+    // An odd number of backticks or html without backticks is invalid
+    if (backtickCount % 2 || (!backtickCount && matches.test(fullText))) {
+      return false;
+    }
+
+    // Text without html is valid
+    if (!matches.test(fullText)) {
+      return true;
+    }
+
+    // < and > must always be between two matching backticks.
+
+    // Whether an opening backtick has been found without a closing pair
+    let openBacktick = false;
+
+    for (const char of fullText) {
+      if (char === '`') {
+        openBacktick = !openBacktick;
+      } else if (matches.test(char) && !openBacktick) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+}

tslint.json

@@ -119,6 +119,7 @@
       true,
       "./tools/package-tools/rollup-globals.ts",
       "src/+(lib|cdk|material-examples|material-experimental|cdk-experimental)/**/*.ts"
-    ]
+    ],
+    "no-unescaped-html-tag": true
   }
 }