[system] Array reject on spacing transformation fixed

docs/src/pages/customization/spacing/spacing.md

@@ -38,7 +38,7 @@ theme.spacing(2); // = 0.25 * 2rem = 0.5rem = 8px
 
 ```js
 const theme = createMuiTheme({
-  spacing: factor => [0, 4, 8, 16, 32, 64][factor],
+  spacing: [0, 4, 8, 16, 32, 64],
 });
 
 theme.spacing(2); // = 8

packages/material-ui-system/src/index.js

@@ -16,6 +16,7 @@ export { default as shadows } from './shadows';
 export { default as sizing } from './sizing';
 export * from './sizing';
 export { default as spacing } from './spacing';
+export * from './spacing';
 export { default as style } from './style';
 export { default as typography } from './typography';
 export * from './typography';

packages/material-ui-system/src/spacing.js

@@ -74,11 +74,20 @@ const spacingKeys = [
   'paddingY',
 ];
 
-function getTransformer(theme) {
+export function createUnarySpacing(theme) {
   const themeSpacing = theme.spacing || 8;
 
   if (typeof themeSpacing === 'number') {
-    return abs => themeSpacing * abs;
+    return abs => {
+      if (process.env.NODE_ENV !== 'production') {
+        if (typeof abs !== 'number') {
+          console.error(
+            `@material-ui/system: expected spacing argument to be a number, got ${abs}.`,
+          );
+        }
+      }
+      return themeSpacing * abs;
+    };
   }
 
   if (Array.isArray(themeSpacing)) {
@@ -144,7 +153,7 @@ function getStyleFromPropValue(cssProperties, transformer) {
 
 function spacing(props) {
   const theme = props.theme;
-  const transformer = getTransformer(theme);
+  const transformer = createUnarySpacing(theme);
 
   return Object.keys(props)
     .map(prop => {

packages/material-ui/src/styles/createSpacing.js

@@ -1,3 +1,5 @@
+import { createUnarySpacing } from '@material-ui/system';
+
 let warnOnce;
 
 export default function createSpacing(spacingInput = 8) {
@@ -6,32 +8,12 @@ export default function createSpacing(spacingInput = 8) {
     return spacingInput;
   }
 
-  // All components align to an 8dp square baseline grid for mobile, tablet, and desktop.
-  // https://material.io/design/layout/understanding-layout.html#pixel-density
-  let transform;
-
-  if (typeof spacingInput === 'function') {
-    transform = spacingInput;
-  } else {
-    if (process.env.NODE_ENV !== 'production') {
-      if (typeof spacingInput !== 'number') {
-        console.error(
-          [
-            `Material-UI: the \`theme.spacing\` value (${spacingInput}) is invalid.`,
-            'It should be a number or a function.',
-          ].join('\n'),
-        );
-      }
-    }
-    transform = factor => {
-      if (process.env.NODE_ENV !== 'production') {
-        if (typeof factor !== 'number') {
-          console.error(`Expected spacing argument to be a number, got ${factor}`);
-        }
-      }
-      return spacingInput * factor;
-    };
-  }
+  // Material Design layouts are visually balanced. Most measurements align to an 8dp grid applied, which aligns both spacing and the overall layout.
+  // Smaller components, such as icons and type, can align to a 4dp grid.
+  // https://material.io/design/layout/understanding-layout.html#usage
+  const transform = createUnarySpacing({
+    spacing: spacingInput,
+  });
 
   const spacing = (...args) => {
     if (process.env.NODE_ENV !== 'production') {

packages/material-ui/src/styles/createSpacing.test.js

@@ -1,20 +1,20 @@
-import { assert } from 'chai';
+import { expect } from 'chai';
 import createSpacing from './createSpacing';
 import consoleErrorMock from 'test/utils/consoleErrorMock';
 
 describe('createSpacing', () => {
   it('should work as expected', () => {
     let spacing;
     spacing = createSpacing();
-    assert.strictEqual(spacing(1), 8);
+    expect(spacing(1)).to.equal(8);
     spacing = createSpacing(10);
-    assert.strictEqual(spacing(1), 10);
-    spacing = createSpacing(factor => [0, 8, 16][factor]);
-    assert.strictEqual(spacing(2), 16);
+    expect(spacing(1)).to.equal(10);
+    spacing = createSpacing([0, 8, 16]);
+    expect(spacing(2)).to.equal(16);
     spacing = createSpacing(factor => factor ** 2);
-    assert.strictEqual(spacing(2), 4);
+    expect(spacing(2)).to.equal(4);
     spacing = createSpacing(factor => `${0.25 * factor}rem`);
-    assert.strictEqual(spacing(2), '0.5rem');
+    expect(spacing(2)).to.equal('0.5rem');
   });
 
   it('should support recursion', () => {
@@ -25,17 +25,17 @@ describe('createSpacing', () => {
   it('should support a default value when no arguments are provided', () => {
     let spacing;
     spacing = createSpacing();
-    assert.strictEqual(spacing(), 8);
+    expect(spacing()).to.equal(8);
     spacing = createSpacing(factor => `${0.25 * factor}rem`);
-    assert.strictEqual(spacing(), '0.25rem');
+    expect(spacing()).to.equal('0.25rem');
   });
 
   it('should support multiple arguments', () => {
     let spacing;
     spacing = createSpacing();
-    assert.strictEqual(spacing(1, 2), '8px 16px');
+    expect(spacing(1, 2)).to.equal('8px 16px');
     spacing = createSpacing(factor => `${0.25 * factor}rem`);
-    assert.strictEqual(spacing(1, 2), '0.25rem 0.5rem');
+    expect(spacing(1, 2)).to.equal('0.25rem 0.5rem');
   });
 
   describe('warnings', () => {
@@ -47,20 +47,22 @@ describe('createSpacing', () => {
       consoleErrorMock.reset();
     });
 
+    // TODO v5: remove
     it('should warn for the deprecated API', () => {
       const spacing = createSpacing(11);
-      assert.strictEqual(spacing.unit, 11);
-      assert.strictEqual(consoleErrorMock.callCount(), 1);
-      assert.include(consoleErrorMock.args()[0][0], 'theme.spacing.unit usage has been deprecated');
+      expect(spacing.unit).to.equal(11);
+      expect(consoleErrorMock.callCount()).to.equal(1);
+      expect(consoleErrorMock.args()[0][0]).to.include(
+        'theme.spacing.unit usage has been deprecated',
+      );
     });
 
     it('should warn for wrong input', () => {
       createSpacing({
         unit: 4,
       });
-      assert.strictEqual(consoleErrorMock.callCount(), 1);
-      assert.include(
-        consoleErrorMock.args()[0][0],
+      expect(consoleErrorMock.callCount()).to.equal(1);
+      expect(consoleErrorMock.args()[0][0]).to.include(
         'the `theme.spacing` value ([object Object]) is invalid',
       );
     });