fix: remove local macros upon parse error (#3114)

Close all groups after parse, in particular in case of parse error,
completing `Namespace`'s simulation of local definitions.

Fixes #3122

Co-authored-by: ylemkimon <y@ylem.kim>

src/MacroExpander.js

@@ -74,6 +74,14 @@ export default class MacroExpander implements MacroContextInterface {
         this.macros.endGroup();
     }
 
+    /**
+     * Ends all currently nested groups (if any), restoring values before the
+     * groups began.  Useful in case of an error in the middle of parsing.
+     */
+    endGroups() {
+        this.macros.endGroups();
+    }
+
     /**
      * Returns the topmost token on the stack, without expanding it.
      * Similar in behavior to TeX's `\futurelet`.

src/Namespace.js

@@ -57,6 +57,16 @@ export default class Namespace<Value> {
         }
     }
 
+    /**
+     * Ends all currently nested groups (if any), restoring values before the
+     * groups began.  Useful in case of an error in the middle of parsing.
+     */
+    endGroups() {
+        while (this.undefStack.length > 0) {
+            this.endGroup();
+        }
+    }
+
     /**
      * Detect whether `name` has a definition.  Equivalent to
      * `get(name) != null`.

src/Parser.js

@@ -130,6 +130,7 @@ export default class Parser {
             this.gullet.macros.set("\\color", "\\textcolor");
         }
 
+        try {
             // Try to parse the input
             const parse = this.parseExpression(false);
 
@@ -140,7 +141,13 @@ export default class Parser {
             if (!this.settings.globalGroup) {
                 this.gullet.endGroup();
             }
+
             return parse;
+
+        // Close any leftover groups in case of a parse error.
+        } finally {
+            this.gullet.endGroups();
+        }
     }
 
     static endOfExpression: string[] = ["}", "\\endgroup", "\\end", "\\right", "&"];

test/katex-spec.js

@@ -3440,6 +3440,12 @@ describe("A macro expander", function() {
         expect(macros["\\foo"]).toBeFalsy();
     });
 
+    it("\\def doesn't change settings.macros on error", () => {
+        const macros = {};
+        expect`\def\foo{c^}\foo`.not.toParse(new Settings({macros}));
+        expect(macros["\\foo"]).toBeFalsy();
+    });
+
     it("\\def changes settings.macros with globalGroup", () => {
         const macros = {};
         expect`\gdef\foo{1}`.toParse(new Settings({macros, globalGroup: true}));