fix: #1455 implicit multiplication of a fraction with unit 'in' is in…

…correct (#3315)

src/expression/parse.js

@@ -1122,7 +1122,7 @@ export const createParse = /* #__PURE__ */ factory(name, dependencies, ({
           getTokenSkipNewline(state)
 
           // Match the "symbol" part of the pattern, or a left parenthesis
-          if (state.tokenType === TOKENTYPE.SYMBOL || state.token === '(') {
+          if (state.tokenType === TOKENTYPE.SYMBOL || state.token === '(' || state.token === 'in') {
             // We've matched the pattern "number / number symbol".
             // Rewind once and build the "number / number" node; the symbol will be consumed later
             Object.assign(state, tokenStates.pop())

test/unit-tests/expression/parse.test.js

@@ -1480,6 +1480,15 @@ describe('parse', function () {
       assert.strictEqual(parseAndStringifyWithParens('8.314 J/mol K'), '(8.314 J) / (mol K)')
     })
 
+    it('should handle precedence with implicit multiplication, division, and the "in" operator', function () {
+      assert.strictEqual(parseAndStringifyWithParens('1/2 in'), '(1 / 2) in')
+      assert.strictEqual(parseAndStringifyWithParens('1/2 kg'), '(1 / 2) kg')
+      assert.strictEqual(parseAndStringifyWithParens('3 kg in lb'), '(3 kg) in lb')
+      assert.strictEqual(parseAndStringifyWithParens('2 m / 1 s'), '(2 m) / (1 s)')
+      assert.strictEqual(parseAndStringifyWithParens('5 / 10 in'), '(5 / 10) in')
+      assert.strictEqual(parseAndStringifyWithParens('10 lb + 1/2 lb'), '(10 lb) + ((1 / 2) lb)')
+    })
+
     it('should throw an error when having an implicit multiplication between two numbers', function () {
       assert.throws(function () { math.parse('2 3') }, /Unexpected part "3"/)
       assert.throws(function () { math.parse('2 * 3 4') }, /Unexpected part "4"/)