Add support for postfix modifier

README.md

@@ -18,7 +18,7 @@ twMerge('px-2 py-1 bg-red hover:bg-dark-red', 'p-3 bg-[#B91C1C]')
 // → 'hover:bg-dark-red p-3 bg-[#B91C1C]'
 ```
 
--   Supports Tailwind v3.0 up to v3.3 (except line-height shorthand, tracked in [#211](https://github.com/dcastil/tailwind-merge/issues/211); if you use Tailwind v2, use [tailwind-merge v0.9.0](https://github.com/dcastil/tailwind-merge/tree/v0.9.0))
+-   Supports Tailwind v3.0 up to v3.3 (if you use Tailwind v2, use [tailwind-merge v0.9.0](https://github.com/dcastil/tailwind-merge/tree/v0.9.0))
 -   Works in all modern browsers and Node >=12
 -   Fully typed
 -   [Check bundle size on Bundlephobia](https://bundlephobia.com/package/tailwind-merge)

docs/api-reference.md

@@ -100,15 +100,24 @@ const customTwMerge = extendTailwindMerge({
         //     Classes here: foo, foo-2, bar-baz, bar-baz-1, bar-baz-2
         foo: ['foo', 'foo-2', { 'bar-baz': ['', '1', '2'] }],
         //   ↓ Functions can also be used to match classes.
-        //     Classes here: qux-auto, qux-1000, qux-1001, …
+        //     Classes here: qux-auto, qux-1000, qux-1001,…
         bar: [{ qux: ['auto', (value) => Number(value) >= 1000] }],
+        baz: ['baz-sm', 'baz-md', 'baz-lg'],
     },
     // ↓ Here you can define additional conflicts across different groups
     conflictingClassGroups: {
-        // ↓ ID of class group which creates a conflict with …
-        //     ↓ … classes from groups with these IDs
+        // ↓ ID of class group which creates a conflict with…
+        //     ↓ …classes from groups with these IDs
+        // In this case `twMerge('qux-auto foo') → 'foo'`
         foo: ['bar'],
     },
+    // ↓ Here you can define conflicts between the postfix modifier of a group and a different class group.
+    conflictingClassGroupModifiers: {
+        // ↓ ID of class group whose postfix modifier creates a conflict with…
+        //     ↓ …classes from groups with these IDs
+        // In this case `twMerge('qux-auto baz-sm/1000') → 'baz-sm/1000'`
+        baz: ['bar'],
+    },
 })
 ```
 
@@ -148,11 +157,16 @@ const customTwMerge = createTailwindMerge(() => {
             ...defaultConfig.classGroups,
             foo: ['foo', 'foo-2', { 'bar-baz': ['', '1', '2'] }],
             bar: [{ qux: ['auto', (value) => Number(value) >= 1000] }],
+            baz: ['baz-sm', 'baz-md', 'baz-lg'],
         },
         conflictingClassGroups: {
             ...defaultConfig.conflictingClassGroups,
             foo: ['bar'],
         },
+        conflictingClassGroupModifiers: {
+            ...defaultConfig.conflictingClassGroupModifiers,
+            baz: ['bar'],
+        },
     }
 })
 ```

docs/configuration.md

@@ -41,6 +41,10 @@ const tailwindMergeConfig = {
     conflictingClassGroups: {
         // Conflicts between class groups are defined here
     },
+    conflictingClassGroupModifiers: {
+        // Conflicts between postfox modifier of a class group and another class group are defined here
+    },
+    }
 }
 ```
 
@@ -92,9 +96,9 @@ Sometimes there are conflicts across Tailwind classes which are more complex tha
 
 One example is the combination of the classes `px-3` (setting `padding-left` and `padding-right`) and `pr-4` (setting `padding-right`).
 
-If they are passed to `twMerge` as `pr-4 px-3`, I think you most likely intend to apply `padding-left` and `padding-right` from the `px-3` class and want `pr-4` to be removed, indicating that both these classes should belong to a single class group.
+If they are passed to `twMerge` as `pr-4 px-3`, you most likely intend to apply `padding-left` and `padding-right` from the `px-3` class and want `pr-4` to be removed, indicating that both these classes should belong to a single class group.
 
-But if they are passed to `twMerge` as `px-3 pr-4`, I assume you want to set the `padding-right` from `pr-4` but still want to apply the `padding-left` from `px-3`, so `px-3` shouldn't be removed when inserting the classes in this order, indicating they shouldn't be in the same class group.
+But if they are passed to `twMerge` as `px-3 pr-4`, you want to set the `padding-right` from `pr-4` but still want to apply the `padding-left` from `px-3`, so `px-3` shouldn't be removed when inserting the classes in this order, indicating they shouldn't be in the same class group.
 
 To summarize, `px-3` should stand in conflict with `pr-4`, but `pr-4` should not stand in conflict with `px-3`. To achieve this, we need to define asymmetric conflicts across class groups.
 
@@ -110,6 +114,18 @@ If a class group _creates_ a conflict, it means that if it appears in a class li
 
 When we think of our example, the `px` class group creates a conflict which is received by the class groups `pr` and `pl`. This way `px-3` removes a preceding `pr-4`, but not the other way around.
 
+### Postfix modifiers conflicting with class groups
+
+Tailwind CSS allows postfix modifiers for some classes. E.g. you can set font-size and line-height together with `text-lg/7` with `/7` being the postfix modifier. This means that any line-height classes preceding a font-size class with a modifier should be removed.
+
+For this tailwind-merge has the `conflictingClassGroupModifiers` object in its config with the same shape as `conflictingClassGroups` explained in the [section above](#conflicting-class-groups). This time the key is the ID of a class group whose modifier _creates_ a conflict and the value is an array of IDs of class groups which _receive_ the conflict.
+
+```ts
+const conflictingClassGroupModifiers = {
+    'font-size': ['leading'],
+}
+```
+
 ### Theme
 
 In the Tailwind config you can modify theme scales. tailwind-merge follows the same keys for the theme scales, but doesn't support all of them. tailwind-merge only supports theme scales which are used in multiple class groups to save bundle size (more info to that in [PR 55](https://github.com/dcastil/tailwind-merge/pull/55)). At the moment these are:
@@ -158,11 +174,16 @@ const customTwMerge = extendTailwindMerge({
     classGroups: {
         foo: ['foo', 'foo-2', { 'bar-baz': ['', '1', '2'] }],
         bar: [{ qux: ['auto', (value) => Number(value) >= 1000] }],
+        baz: ['baz-sm', 'baz-md', 'baz-lg'],
     },
     // ↓ Here you can define additional conflicts across class groups
     conflictingClassGroups: {
         foo: ['bar'],
     },
+    // ↓ Define conflicts between postfix modifiers and class groups
+    conflictingClassGroupModifiers: {
+        baz: ['bar'],
+    },
 })
 ```
 
@@ -181,10 +202,14 @@ const customTwMerge = createTailwindMerge(() => ({
     classGroups: {
         foo: ['foo', 'foo-2', { 'bar-baz': ['', '1', '2'] }],
         bar: [{ qux: ['auto', (value) => Number(value) >= 1000] }],
+        baz: ['baz-sm', 'baz-md', 'baz-lg'],
     },
     conflictingClassGroups: {
         foo: ['bar'],
     },
+    conflictingClassGroupModifiers: {
+        baz: ['bar'],
+    },
 }))
 ```
 

docs/features.md

@@ -75,6 +75,12 @@ twMerge('!p-3 !p-4 p-5') // → '!p-4 p-5'
 twMerge('!right-2 !-inset-x-1') // → '!-inset-x-1'
 ```
 
+## Supports postfix modifiers
+
+```ts
+twMerge('text-sm leading-6 text-lg/7') // → 'text-lg/7'
+```
+
 ## Preserves non-Tailwind classes
 
 ```ts
@@ -100,6 +106,8 @@ twMerge('some-class', [undefined, ['another-class', false]], ['third-class'])
 // → 'some-class another-class third-class'
 ```
 
+Why no object support? [Read here](https://github.com/dcastil/tailwind-merge/discussions/137#discussioncomment-3481605).
+
 ---
 
 Next: [Configuration](./configuration.md)

src/lib/class-utils.ts

@@ -15,6 +15,7 @@ const CLASS_PART_SEPARATOR = '-'
 
 export function createClassUtils(config: Config) {
     const classMap = createClassMap(config)
+    const { conflictingClassGroups, conflictingClassGroupModifiers = {} } = config
 
     function getClassGroupId(className: string) {
         const classParts = className.split(CLASS_PART_SEPARATOR)
@@ -27,8 +28,14 @@ export function createClassUtils(config: Config) {
         return getGroupRecursive(classParts, classMap) || getGroupIdForArbitraryProperty(className)
     }
 
-    function getConflictingClassGroupIds(classGroupId: ClassGroupId) {
-        return config.conflictingClassGroups[classGroupId] || []
+    function getConflictingClassGroupIds(classGroupId: ClassGroupId, hasPostfixModifier: boolean) {
+        const conflicts = conflictingClassGroups[classGroupId] || []
+
+        if (hasPostfixModifier && conflictingClassGroupModifiers[classGroupId]) {
+            return [...conflicts, ...conflictingClassGroupModifiers[classGroupId]!]
+        }
+
+        return conflicts
     }
 
     return {

src/lib/default-config.ts

@@ -1,4 +1,5 @@
 import { fromTheme } from './from-theme'
+import { Config } from './types'
 import {
     isAny,
     isArbitraryLength,
@@ -1763,5 +1764,8 @@ export function getDefaultConfig() {
             'scroll-px': ['scroll-pr', 'scroll-pl'],
             'scroll-py': ['scroll-pt', 'scroll-pb'],
         },
-    } as const
+        conflictingClassGroupModifiers: {
+            'font-size': ['leading'],
+        },
+    } as const satisfies Config
 }

src/lib/merge-classlist.ts

@@ -20,16 +20,39 @@ export function mergeClassList(classList: string, configUtils: ConfigUtils) {
             .trim()
             .split(SPLIT_CLASSES_REGEX)
             .map((originalClassName) => {
-                const { modifiers, hasImportantModifier, baseClassName } =
-                    splitModifiers(originalClassName)
+                const {
+                    modifiers,
+                    hasImportantModifier,
+                    baseClassName,
+                    maybePostfixModifierPosition,
+                } = splitModifiers(originalClassName)
 
-                const classGroupId = getClassGroupId(baseClassName)
+                let classGroupId = getClassGroupId(
+                    maybePostfixModifierPosition
+                        ? baseClassName.substring(0, maybePostfixModifierPosition)
+                        : baseClassName,
+                )
+
+                let hasPostfixModifier = Boolean(maybePostfixModifierPosition)
 
                 if (!classGroupId) {
-                    return {
-                        isTailwindClass: false as const,
-                        originalClassName,
+                    if (!maybePostfixModifierPosition) {
+                        return {
+                            isTailwindClass: false as const,
+                            originalClassName,
+                        }
+                    }
+
+                    classGroupId = getClassGroupId(baseClassName)
+
+                    if (!classGroupId) {
+                        return {
+                            isTailwindClass: false as const,
+                            originalClassName,
+                        }
                     }
+
+                    hasPostfixModifier = false
                 }
 
                 const variantModifier = sortModifiers(modifiers).join(':')
@@ -43,6 +66,7 @@ export function mergeClassList(classList: string, configUtils: ConfigUtils) {
                     modifierId,
                     classGroupId,
                     originalClassName,
+                    hasPostfixModifier,
                 }
             })
             .reverse()
@@ -52,7 +76,7 @@ export function mergeClassList(classList: string, configUtils: ConfigUtils) {
                     return true
                 }
 
-                const { modifierId, classGroupId } = parsed
+                const { modifierId, classGroupId, hasPostfixModifier } = parsed
 
                 const classId = modifierId + classGroupId
 
@@ -62,7 +86,7 @@ export function mergeClassList(classList: string, configUtils: ConfigUtils) {
 
                 classGroupsInConflict.add(classId)
 
-                getConflictingClassGroupIds(classGroupId).forEach((group) =>
+                getConflictingClassGroupIds(classGroupId, hasPostfixModifier).forEach((group) =>
                     classGroupsInConflict.add(modifierId + group),
                 )
 

src/lib/modifier-utils.ts

@@ -4,29 +4,41 @@ export const IMPORTANT_MODIFIER = '!'
 
 export function createSplitModifiers(config: Config) {
     const separator = config.separator || ':'
+    const isSeparatorSingleCharacter = separator.length === 1
+    const firstSeparatorCharacter = separator[0]
+    const separatorLength = separator.length
 
     // splitModifiers inspired by https://github.com/tailwindlabs/tailwindcss/blob/v3.2.2/src/util/splitAtTopLevelOnly.js
     return function splitModifiers(className: string) {
+        const modifiers = []
+
         let bracketDepth = 0
-        let modifiers = []
         let modifierStart = 0
+        let postfixModifierPosition: number | undefined
 
         for (let index = 0; index < className.length; index++) {
-            let char = className[index]
+            let currentCharacter = className[index]
 
-            if (bracketDepth === 0 && char === separator[0]) {
+            if (bracketDepth === 0) {
                 if (
-                    separator.length === 1 ||
-                    className.slice(index, index + separator.length) === separator
+                    currentCharacter === firstSeparatorCharacter &&
+                    (isSeparatorSingleCharacter ||
+                        className.slice(index, index + separatorLength) === separator)
                 ) {
                     modifiers.push(className.slice(modifierStart, index))
-                    modifierStart = index + separator.length
+                    modifierStart = index + separatorLength
+                    continue
+                }
+
+                if (currentCharacter === '/') {
+                    postfixModifierPosition = index
+                    continue
                 }
             }
 
-            if (char === '[') {
+            if (currentCharacter === '[') {
                 bracketDepth++
-            } else if (char === ']') {
+            } else if (currentCharacter === ']') {
                 bracketDepth--
             }
         }
@@ -39,10 +51,16 @@ export function createSplitModifiers(config: Config) {
             ? baseClassNameWithImportantModifier.substring(1)
             : baseClassNameWithImportantModifier
 
+        const maybePostfixModifierPosition =
+            postfixModifierPosition && postfixModifierPosition > modifierStart
+                ? postfixModifierPosition - modifierStart
+                : undefined
+
         return {
             modifiers,
             hasImportantModifier,
             baseClassName,
+            maybePostfixModifierPosition,
         }
     }
 }

src/lib/types.ts

@@ -34,10 +34,16 @@ export interface Config {
     /**
      * Conflicting classes across groups.
      * The key is ID of class group which creates conflict, values are IDs of class groups which receive a conflict.
-     * A class group is ID is the key of a class group in classGroups object.
+     * A class group ID is the key of a class group in classGroups object.
      * @example { gap: ['gap-x', 'gap-y'] }
      */
     conflictingClassGroups: Record<ClassGroupId, readonly ClassGroupId[]>
+    /**
+     * Postfix modifiers conflicting with other class groups.
+     * A class group ID is the key of a class group in classGroups object.
+     * @example { 'font-size': ['leading'] }
+     */
+    conflictingClassGroupModifiers?: Record<ClassGroupId, readonly ClassGroupId[]>
 }
 
 export type ThemeObject = Record<string, ClassGroup>

tests/modifiers.test.ts

@@ -1,10 +1,38 @@
-import { twMerge } from '../src'
+import { createTailwindMerge, twMerge } from '../src'
 
-test('conflicts across modifiers', () => {
+test('conflicts across prefix modifiers', () => {
     expect(twMerge('hover:block hover:inline')).toBe('hover:inline')
     expect(twMerge('hover:block hover:focus:inline')).toBe('hover:block hover:focus:inline')
     expect(twMerge('hover:block hover:focus:inline focus:hover:inline')).toBe(
         'hover:block focus:hover:inline',
     )
     expect(twMerge('focus-within:inline focus-within:block')).toBe('focus-within:block')
 })
+
+test('conflicts across postfix modifiers', () => {
+    expect(twMerge('text-lg/7 text-lg/8')).toBe('text-lg/8')
+    expect(twMerge('text-lg/none leading-9')).toBe('text-lg/none leading-9')
+    expect(twMerge('leading-9 text-lg/none')).toBe('text-lg/none')
+    expect(twMerge('w-full w-1/2')).toBe('w-1/2')
+
+    const customTwMerge = createTailwindMerge(() => ({
+        cacheSize: 10,
+        theme: {},
+        classGroups: {
+            foo: ['foo-1/2', 'foo-2/3'],
+            bar: ['bar-1', 'bar-2'],
+            baz: ['baz-1', 'baz-2'],
+        },
+        conflictingClassGroups: {},
+        conflictingClassGroupModifiers: {
+            baz: ['bar'],
+        },
+    }))
+
+    expect(customTwMerge('foo-1/2 foo-2/3')).toBe('foo-2/3')
+    expect(customTwMerge('bar-1 bar-2')).toBe('bar-2')
+    expect(customTwMerge('bar-1 baz-1')).toBe('bar-1 baz-1')
+    expect(customTwMerge('bar-1/2 bar-2')).toBe('bar-2')
+    expect(customTwMerge('bar-2 bar-1/2')).toBe('bar-1/2')
+    expect(customTwMerge('bar-1 baz-1/2')).toBe('baz-1/2')
+})

tests/tailwind-css-versions.test.ts

@@ -1,6 +1,7 @@
 import { twMerge } from '../src'
 
 test('supports Tailwind CSS v3.3 features', () => {
+    expect(twMerge('text-red text-lg/7 text-lg/8')).toBe('text-red text-lg/8')
     expect(
         twMerge(
             'start-0 start-1',