tailwindcss/src/lib/substituteClassApplyAtRules.js

import _ from 'lodash'
import selectorParser from 'postcss-selector-parser'
import postcss from 'postcss'
import didYouMean from 'didyoumean'
import substituteTailwindAtRules from './substituteTailwindAtRules'
import evaluateTailwindFunctions from './evaluateTailwindFunctions'
import substituteVariantsAtRules from './substituteVariantsAtRules'
import substituteResponsiveAtRules from './substituteResponsiveAtRules'
import convertLayerAtRulesToControlComments from './convertLayerAtRulesToControlComments'
import substituteScreenAtRules from './substituteScreenAtRules'
import prefixSelector from '../util/prefixSelector'
import { useMemo } from '../util/useMemo'

function hasAtRule(css, atRule) {
  let foundAtRule = false

  css.walkAtRules(atRule, () => {
    foundAtRule = true
    return false
  })

  return foundAtRule
}

function cloneWithoutChildren(node) {
  if (node.type === 'atrule') {
    return postcss.atRule({ name: node.name, params: node.params })
  }

  if (node.type === 'rule') {
    return postcss.rule({ name: node.name, selectors: node.selectors })
  }

  const clone = node.clone()
  clone.removeAll()
  return clone
}

const tailwindApplyPlaceholder = selectorParser.attribute({
  attribute: '__TAILWIND-APPLY-PLACEHOLDER__',
})

function generateRulesFromApply({ rule, utilityName: className, classPosition }, replaceWiths) {
  const parser = selectorParser((selectors) => {
    let i = 0
    selectors.walkClasses((c) => {
      if (classPosition === i++ && c.value === className) {
        c.replaceWith(tailwindApplyPlaceholder)
      }
    })
  })

  const processedSelectors = _.flatMap(rule.selectors, (selector) => {
    // You could argue we should make this replacement at the AST level, but if we believe
    // the placeholder string is safe from collisions then it is safe to do this is a simple
    // string replacement, and much, much faster.
    return replaceWiths.map((replaceWith) =>
      parser.processSync(selector).replace('[__TAILWIND-APPLY-PLACEHOLDER__]', replaceWith)
    )
  })

  const cloned = rule.clone()
  let current = cloned
  let parent = rule.parent

  while (parent && parent.type !== 'root') {
    const parentClone = cloneWithoutChildren(parent)

    parentClone.append(current)
    current.parent = parentClone
    current = parentClone
    parent = parent.parent
  }

  cloned.selectors = processedSelectors
  return current
}

const extractUtilityNamesParser = selectorParser((selectors) => {
  let classes = []
  selectors.walkClasses((c) => classes.push(c.value))
  return classes
})

const extractUtilityNames = useMemo(
  (selector) => extractUtilityNamesParser.transformSync(selector),
  (selector) => selector
)

const cloneRuleWithParent = useMemo(
  (rule) => rule.clone({ parent: rule.parent }),
  (rule) => rule
)

function buildUtilityMap(css, lookupTree) {
  let index = 0
  const utilityMap = {}

  function handle(getRule, rule) {
    const utilityNames = extractUtilityNames(rule.selector)

    utilityNames.forEach((utilityName, i) => {
      if (utilityMap[utilityName] === undefined) {
        utilityMap[utilityName] = []
      }

      utilityMap[utilityName].push({
        index,
        utilityName,
        classPosition: i,
        ...getRule(rule),
      })
      index++
    })
  }

  // Lookup tree is the big lookup tree, making the rule lazy allows us to save
  // some memory because we don't need everything.
  lookupTree.walkRules(
    handle.bind(null, (rule) => ({
      get rule() {
        return cloneRuleWithParent(rule)
      },
    }))
  )

  // This is the end user's css. This might contain rules that we want to
  // apply. We want immediate copies of everything in case that we have user
  // defined classes that are recursively applied. Down below we are modifying
  // the rules directly. We could do a better solution where we keep track of a
  // dependency tree, but that is a bit more complex. Might revisit later,
  // we'll see how this turns out!
  css.walkRules(handle.bind(null, (rule) => ({ rule: cloneRuleWithParent(rule) })))

  return utilityMap
}

function mergeAdjacentRules(initialRule, rulesToInsert) {
  let previousRule = initialRule

  rulesToInsert.forEach((toInsert) => {
    if (
      toInsert.type === 'rule' &&
      previousRule.type === 'rule' &&
      toInsert.selector === previousRule.selector
    ) {
      previousRule.append(toInsert.nodes)
    } else if (
      toInsert.type === 'atrule' &&
      previousRule.type === 'atrule' &&
      toInsert.params === previousRule.params
    ) {
      const merged = mergeAdjacentRules(
        previousRule.nodes[previousRule.nodes.length - 1],
        toInsert.nodes
      )

      previousRule.append(merged)
    } else {
      previousRule = toInsert
    }

    toInsert.walk((n) => {
      if (n.nodes && n.nodes.length === 0) {
        n.remove()
      }
    })
  })

  return rulesToInsert.filter((r) => r.nodes.length > 0)
}

function makeExtractUtilityRules(css, lookupTree, config) {
  const utilityMap = buildUtilityMap(css, lookupTree)

  return function extractUtilityRules(utilityNames, rule) {
    const combined = []

    utilityNames.forEach((utilityName) => {
      if (utilityMap[utilityName] === undefined) {
        // Look for prefixed utility in case the user has goofed
        const prefixedUtility = prefixSelector(config.prefix, `.${utilityName}`).slice(1)

        if (utilityMap[prefixedUtility] !== undefined) {
          throw rule.error(
            `The \`${utilityName}\` class does not exist, but \`${prefixedUtility}\` does. Did you forget the prefix?`
          )
        }

        const suggestedClass = didYouMean(utilityName, Object.keys(utilityMap))
        const suggestionMessage = suggestedClass ? `, but \`${suggestedClass}\` does` : ''

        throw rule.error(
          `The \`${utilityName}\` class does not exist${suggestionMessage}. If you're sure that \`${utilityName}\` exists, make sure that any \`@import\` statements are being properly processed before Tailwind CSS sees your CSS, as \`@apply\` can only be used for classes in the same CSS tree.`,
          { word: utilityName }
        )
      }

      combined.push(...utilityMap[utilityName])
    })

    return combined.sort((a, b) => a.index - b.index)
  }
}

function findParent(rule, predicate) {
  let parent = rule.parent
  while (parent) {
    if (predicate(parent)) {
      return parent
    }

    parent = parent.parent
  }

  throw new Error('No parent could be found')
}

function processApplyAtRules(css, lookupTree, config) {
  const extractUtilityRules = makeExtractUtilityRules(css, lookupTree, config)

  do {
    css.walkAtRules('apply', (applyRule) => {
      const parent = applyRule.parent // Direct parent
      const nearestParentRule = findParent(applyRule, (r) => r.type === 'rule')
      const currentUtilityNames = extractUtilityNames(nearestParentRule.selector)

      const [
        importantEntries,
        applyUtilityNames,
        important = importantEntries.length > 0,
      ] = _.partition(applyRule.params.split(/[\s\t\n]+/g), (n) => n === '!important')

      if (_.intersection(applyUtilityNames, currentUtilityNames).length > 0) {
        const currentUtilityName = _.intersection(applyUtilityNames, currentUtilityNames)[0]
        throw parent.error(
          `You cannot \`@apply\` the \`${currentUtilityName}\` utility here because it creates a circular dependency.`
        )
      }

      // Extract any post-apply declarations and re-insert them after apply rules
      const afterRule = parent.clone({ raws: {} })
      afterRule.nodes = afterRule.nodes.slice(parent.index(applyRule) + 1)
      parent.nodes = parent.nodes.slice(0, parent.index(applyRule) + 1)

      // Sort applys to match CSS source order
      const applys = extractUtilityRules(applyUtilityNames, applyRule)

      // Get new rules with the utility portion of the selector replaced with the new selector
      const rulesToInsert = []

      applys.forEach(
        nearestParentRule === parent
          ? (util) => rulesToInsert.push(generateRulesFromApply(util, parent.selectors))
          : (util) => util.rule.nodes.forEach((n) => afterRule.append(n.clone()))
      )

      rulesToInsert.forEach((rule) => {
        if (rule.type === 'atrule') {
          rule.walkRules((rule) => {
            rule.__tailwind = { ...rule.__tailwind, important }
          })
        } else {
          rule.__tailwind = { ...rule.__tailwind, important }
        }
      })

      const { nodes } = _.tap(postcss.root({ nodes: rulesToInsert }), (root) => {
        root.walkDecls((d) => {
          d.important = important
        })
      })

      const mergedRules = mergeAdjacentRules(nearestParentRule, [...nodes, afterRule])

      applyRule.remove()
      parent.after(mergedRules)

      // If the base rule has nothing in it (all applys were pseudo or responsive variants),
      // remove the rule fuggit.
      if (parent.nodes.length === 0) {
        parent.remove()
      }
    })

    // We already know that we have at least 1 @apply rule. Otherwise this
    // function would not have been called. Therefore we can execute this code
    // at least once. This also means that in the best case scenario we only
    // call this 2 times, instead of 3 times.
    // 1st time -> before we call this function
    // 2nd time -> when we check if we have to do this loop again (because do {} while (check))
    // .. instead of
    // 1st time -> before we call this function
    // 2nd time -> when we check the first time (because while (check) do {})
    // 3rd time -> when we re-check to see if we should do this loop again
  } while (hasAtRule(css, 'apply'))

  return css
}

let defaultTailwindTree = null

export default function substituteClassApplyAtRules(config, getProcessedPlugins, configChanged) {
  return function (css) {
    // We can stop already when we don't have any @apply rules. Vue users: you're welcome!
    if (!hasAtRule(css, 'apply')) {
      return css
    }

    // Tree already contains @tailwind rules, don't prepend default Tailwind tree
    if (hasAtRule(css, 'tailwind')) {
      return processApplyAtRules(css, postcss.root(), config)
    }

    // Tree contains no @tailwind rules, so generate all of Tailwind's styles and
    // prepend them to the user's CSS. Important for <style> blocks in Vue components.
    const generateLookupTree =
      configChanged || defaultTailwindTree === null
        ? () => {
            return postcss([
              substituteTailwindAtRules(config, getProcessedPlugins()),
              evaluateTailwindFunctions(config),
              substituteVariantsAtRules(config, getProcessedPlugins()),
              substituteResponsiveAtRules(config),
              convertLayerAtRulesToControlComments(config),
              substituteScreenAtRules(config),
            ])
              .process(
                `
                  @tailwind base;
                  @tailwind components;
                  @tailwind utilities;
                `,
                { from: undefined }
              )
              .then((result) => {
                defaultTailwindTree = result
                return defaultTailwindTree
              })
          }
        : () => Promise.resolve(defaultTailwindTree)

    return generateLookupTree().then((result) => {
      return processApplyAtRules(css, result.root, config)
    })
  }
}