Skip newlines when parsing selectors (#13280)

* replace "\n" with " " when parsing CSS

* add test to ensure important whitespace is preserved

packages/tailwindcss/src/css-parser.test.ts

@@ -600,6 +600,28 @@ describe.each(['Unix', 'Windows'])('Line endings: %s', (lineEndings) => {
         },
       ])
     })
+
+    it('should parse a multi-line selector', () => {
+      expect(parse(['.foo,', '.bar,', '.baz', '{', 'color:red;', '}'].join('\n'))).toEqual([
+        {
+          kind: 'rule',
+          selector: '.foo, .bar, .baz',
+          nodes: [{ kind: 'declaration', property: 'color', value: 'red', important: false }],
+        },
+      ])
+    })
+
+    it('should parse a multi-line selector and preserves important whitespace', () => {
+      expect(
+        parse(['.foo,', '.bar,', '.baz\t\n \n .qux', '{', 'color:red;', '}'].join('\n')),
+      ).toEqual([
+        {
+          kind: 'rule',
+          selector: '.foo, .bar, .baz .qux',
+          nodes: [{ kind: 'declaration', property: 'color', value: 'red', important: false }],
+        },
+      ])
+    })
   })
 
   describe('at-rules', () => {

packages/tailwindcss/src/css-parser.ts

@@ -142,6 +142,16 @@ export function parse(input: string) {
       continue
     }
 
+    // Replace new lines with spaces.
+    else if (char === '\n') {
+      if (current.length === 0) continue
+
+      let last = current[current.length - 1]
+      if (last !== ' ' && last !== '\n' && last !== '\t') {
+        current += ' '
+      }
+    }
+
     // Start of a custom property.
     //
     // Custom properties are very permissive and can contain almost any