feat: 修复 cssCalc 预计算时可能输出重复声明的问题，新增仅在启用 cssCalc 时生效的去重清理

Author: sonofmagic

.changeset/css-calc-duplicate-cleaner.md

@@ -0,0 +1,5 @@
+---
+"@weapp-tailwindcss/postcss": patch
+---
+
+修复 `cssCalc` 预计算时可能输出重复声明的问题，新增仅在启用 `cssCalc` 时生效的去重清理。

packages/postcss/src/pipeline.ts

@@ -4,6 +4,7 @@ import type { IStyleHandlerOptions } from './types'
 import postcssPresetEnv from 'postcss-preset-env'
 import { createColorFunctionalFallback } from './plugins/colorFunctionalFallback'
 import { createContext } from './plugins/ctx'
+import { getCalcDuplicateCleaner } from './plugins/getCalcDuplicateCleaner'
 import { getCalcPlugin } from './plugins/getCalcPlugin'
 import { getCustomPropertyCleaner } from './plugins/getCustomPropertyCleaner'
 import { getPxTransformPlugin } from './plugins/getPxTransformPlugin'
@@ -184,6 +185,21 @@ function createPipelineDefinitions(options: IStyleHandlerOptions): PipelineNodeD
     },
   })
 
+  stages.normal.push({
+    id: 'normal:calc-duplicate-cleaner',
+    stage: 'normal',
+    prepare: () => {
+      const plugin = getCalcDuplicateCleaner(options)
+      return plugin
+        ? {
+            id: 'normal:calc-duplicate-cleaner',
+            stage: 'normal',
+            createPlugin: () => plugin,
+          }
+        : undefined
+    },
+  })
+
   stages.normal.push({
     id: 'normal:custom-property-cleaner',
     stage: 'normal',

packages/postcss/src/plugins/getCalcDuplicateCleaner.ts

@@ -0,0 +1,35 @@
+// 清理由 cssCalc 引入的重复声明，避免输出冗余属性
+import type { AcceptedPlugin } from 'postcss'
+import type { IStyleHandlerOptions } from '../types'
+
+export function getCalcDuplicateCleaner(options: IStyleHandlerOptions): AcceptedPlugin | null {
+  if (!options.cssCalc) {
+    return null
+  }
+
+  return {
+    postcssPlugin: 'postcss-calc-duplicate-cleaner',
+    Rule(rule) {
+      rule.walkDecls((decl) => {
+        const prev = decl.prev()
+        if (!prev || prev.type !== 'decl') {
+          return
+        }
+
+        if (prev.prop !== decl.prop) {
+          return
+        }
+
+        if (prev.important !== decl.important) {
+          return
+        }
+
+        if (prev.value !== decl.value) {
+          return
+        }
+
+        decl.remove()
+      })
+    },
+  }
+}

packages/postcss/test/calc.test.ts

@@ -192,6 +192,20 @@ describe('calc', () => {
     expect(css).toContain('margin-left: calc(var(--spacing)*4);')
   })
 
+  it('removes duplicate literal declarations when cssCalc is enabled', async () => {
+    const code = `.mt-1{ margin-top: 8rpx; margin-top: 8rpx; }`
+
+    const styleHandler = createStyleHandler({
+      isMainChunk: false,
+      cssCalc: true,
+    })
+    const { css } = await styleHandler(code, {
+      isMainChunk: false,
+    })
+    const count = css.match(/margin-top:\s*8rpx;/g)?.length ?? 0
+    expect(count).toBe(1)
+  })
+
   it('cssCalc 传入 --spacing 示例', async () => {
     const code = `page,
 :root {