feat: expose error length and raw error message on ParseError

src/ParseError.js

@@ -12,15 +12,21 @@ import type {AnyParseNode} from "./parseNode";
  * about where in the source string the problem occurred.
  */
 class ParseError {
+    name: "ParseError";
     position: number | void;
-        // Error position based on passed-in Token or ParseNode.
+        // Error start position based on passed-in Token or ParseNode.
+    length: number | void;
+        // Length of affected text based on passed-in Token or ParseNode.
+    rawMessage: string | void;
+        // The underlying error message without any context added.
 
     constructor(
         message: string,               // The error message
         token?: ?Token | AnyParseNode, // An object providing position information
-    ): Error {
+    ): ParseError {
         let error = "KaTeX parse error: " + message;
         let start;
+        let end;
 
         const loc = token && token.loc;
         if (loc && loc.start <= loc.end) {
@@ -31,7 +37,7 @@ class ParseError {
 
             // Prepend some information
             start = loc.start;
-            const end = loc.end;
+            end = loc.end;
             if (start === input.length) {
                 error += " at end of input: ";
             } else {
@@ -60,12 +66,16 @@ class ParseError {
 
         // Some hackery to make ParseError a prototype of Error
         // See http://stackoverflow.com/a/8460753
-        const self = new Error(error);
+        // $FlowFixMe
+        const self: ParseError = new Error(error);
         self.name = "ParseError";
         // $FlowFixMe
         self.__proto__ = ParseError.prototype;
-        // $FlowFixMe
         self.position = start;
+        if (start != null && end != null) {
+            self.length = end - start;
+        }
+        self.rawMessage = message;
         return self;
     }
 }

test/katex-spec.js

@@ -5,6 +5,7 @@ import buildTree from "../src/buildTree";
 import katex from "../katex";
 import parseTree from "../src/parseTree";
 import Options from "../src/Options";
+import ParseError from "../src/ParseError";
 import Settings from "../src/Settings";
 import Style from "../src/Style";
 import {
@@ -3060,6 +3061,53 @@ describe("A parser that does not throw on unsupported commands", function() {
     });
 });
 
+describe("ParseError properties", function() {
+    it("should contain affected position and length information", function() {
+        try {
+            katex.renderToString("1 + \\fraq{}{}");
+
+            // Render is expected to throw, so this should not be called.
+            expect(true).toBe(false);
+        } catch (error) {
+            expect(error).toBeInstanceOf(ParseError);
+            expect(error.message).toBe("KaTeX parse error: Undefined control sequence: \\fraq at position 5: 1 + \\̲f̲r̲a̲q̲{}{}");
+            expect(error.rawMessage).toBe("Undefined control sequence: \\fraq");
+            expect(error.position).toBe(4);
+            expect(error.length).toBe(5);
+        }
+    });
+
+    it("should contain position and length information at end of input", function() {
+        try {
+            katex.renderToString("\\frac{}");
+
+            // Render is expected to throw, so this should not be called.
+            expect(true).toBe(false);
+        } catch (error) {
+            expect(error).toBeInstanceOf(ParseError);
+            expect(error.message).toBe("KaTeX parse error: Unexpected end of input in a macro argument, expected '}' at end of input: \\frac{}");
+            expect(error.rawMessage).toBe("Unexpected end of input in a macro argument, expected '}'");
+            expect(error.position).toBe(7);
+            expect(error.length).toBe(0);
+        }
+    });
+
+    it("should contain no position and length information if unavailable", function() {
+        try {
+            katex.renderToString("\\verb|hello\nworld|");
+
+            // Render is expected to throw, so this should not be called.
+            expect(true).toBe(false);
+        } catch (error) {
+            expect(error).toBeInstanceOf(ParseError);
+            expect(error.message).toBe("KaTeX parse error: \\verb ended by end of line instead of matching delimiter");
+            expect(error.rawMessage).toBe("\\verb ended by end of line instead of matching delimiter");
+            expect(error.position).toBeUndefined();
+            expect(error.length).toBeUndefined();
+        }
+    });
+});
+
 describe("The symbol table integrity", function() {
     it("should treat certain symbols as synonyms", function() {
         expect`<`.toBuildLike`\lt`;