fix: evaluate math expressions with units (#304)

* fix: evaluate math expressions with units

* Add changeset

Author: Sese-Schneider

.changeset/brave-timers-burn.md

@@ -0,0 +1,5 @@
+---
+'@tokens-studio/sd-transforms': patch
+---
+
+fix: evaluate math expressions with units

src/checkAndEvaluateMath.ts

@@ -78,15 +78,9 @@ function splitMultiIntoSingleValues(expr: string): string[] {
 function parseAndReduce(expr: string, fractionDigits = defaultFractionDigits): string | number {
   let result: string | number = expr;
 
-  let evaluated;
-  // Try to evaluate as expr-eval expression
-  try {
-    evaluated = parser.evaluate(`${result}`);
-    if (typeof evaluated === 'number') {
-      result = evaluated;
-    }
-  } catch (ex) {
-    //
+  // Check if expression is already a number
+  if (!isNaN(Number(result))) {
+    return result;
   }
 
   // We check for px unit, then remove it, since these are essentially numbers in tokens context
@@ -108,22 +102,37 @@ function parseAndReduce(expr: string, fractionDigits = defaultFractionDigits): s
   }
   const resultUnit = Array.from(foundUnits)[0] ?? (hasPx ? 'px' : '');
 
-  // Remove it here so we can evaluate expressions like 16px + 24px
-  const calcParsed = parse(noPixExpr, { allowInlineCommnets: false });
+  if (!isNaN(Number(noPixExpr))) {
+    result = Number(noPixExpr);
+  }
 
-  // No expression to evaluate, just return it (in case of number as string e.g. '10')
-  if (calcParsed.nodes.length === 1 && calcParsed.nodes[0].type === 'Number') {
-    return `${result}`;
+  if (typeof result !== 'number') {
+    // Try to evaluate as expr-eval expression
+    let evaluated;
+    try {
+      evaluated = parser.evaluate(`${noPixExpr}`);
+      if (typeof evaluated === 'number') {
+        result = evaluated;
+      }
+    } catch (ex) {
+      // no-op
+    }
   }
 
-  // Attempt to reduce the math expression
-  const reduced = reduceExpression(calcParsed);
-  // E.g. if type is Length, like 4 * 7rem would be 28rem
-  if (reduced) {
-    result = reduced.value;
+  if (typeof result !== 'number') {
+    // Try to evaluate as postcss-calc-ast-parser expression
+    const calcParsed = parse(noPixExpr, { allowInlineCommnets: false });
+
+    // Attempt to reduce the math expression
+    const reduced = reduceExpression(calcParsed);
+    // E.g. if type is Length, like 4 * 7rem would be 28rem
+    if (reduced) {
+      result = reduced.value;
+    }
   }
 
   if (typeof result !== 'number') {
+    // parsing failed, return the original expression
     return result;
   }
 

test/spec/checkAndEvaluateMath.spec.ts

@@ -86,6 +86,27 @@ describe('check and evaluate math', () => {
     ).to.equal(14);
   });
 
+  it('supports expr-eval expressions with units', () => {
+    expect(checkAndEvaluateMath({ value: 'roundTo(4px / 7, 1)', type: 'dimension' })).to.equal(
+      '0.6px',
+    );
+    expect(
+      checkAndEvaluateMath({ value: '8 * 14px roundTo(4 / 7px, 1)', type: 'dimension' }),
+    ).to.equal('112px 0.6px');
+    expect(
+      checkAndEvaluateMath({ value: 'roundTo(4px / 7px, 1) 8 * 14px', type: 'dimension' }),
+    ).to.equal('0.6px 112px');
+    expect(
+      checkAndEvaluateMath({
+        value: 'min(10px, 24px, 5px, 12px, 6px) 8 * 14px',
+        type: 'dimension',
+      }),
+    ).to.equal('5px 112px');
+    expect(
+      checkAndEvaluateMath({ value: 'ceil(roundTo(16px/1.2,0)/2)*2', type: 'dimension' }),
+    ).to.equal('14px');
+  });
+
   it('should support expr eval expressions in combination with regular math', () => {
     expect(checkAndEvaluateMath({ value: 'roundTo(4 / 7, 1) * 24', type: 'dimension' })).to.equal(
       14.4,