v4: Improve DX around completions when prefixes are in use (#1292)

Fixes #1291

- [x] Really needs tests

Author: thecrypticace

packages/tailwindcss-language-server/tests/completions/completions.test.js

@@ -740,6 +740,80 @@ defineTest({
   },
 })
 
+defineTest({
+  name: 'v4: Completions show after a variant arbitrary value, using prefixes',
+  fs: {
+    'app.css': css`
+      @import 'tailwindcss' prefix(tw);
+    `,
+  },
+  prepare: async ({ root }) => ({ client: await createClient({ root }) }),
+  handle: async ({ client }) => {
+    let document = await client.open({
+      lang: 'html',
+      text: '<div class="tw:data-[foo]:">',
+    })
+
+    // <div class="tw:data-[foo]:">
+    //                          ^
+    let completion = await document.completions({ line: 0, character: 26 })
+
+    expect(completion?.items.length).toBe(19236)
+  },
+})
+
+defineTest({
+  name: 'v4: Variant and utility suggestions show prefix when one has been typed',
+  fs: {
+    'app.css': css`
+      @import 'tailwindcss' prefix(tw);
+    `,
+  },
+  prepare: async ({ root }) => ({ client: await createClient({ root }) }),
+  handle: async ({ client }) => {
+    let document = await client.open({
+      lang: 'html',
+      text: '<div class="">',
+    })
+
+    // <div class="">
+    //            ^
+    let completion = await document.completions({ line: 0, character: 12 })
+
+    expect(completion?.items.length).toBe(19237)
+
+    // Verify that variants and utilities are all prefixed
+    let prefixed = completion.items.filter((item) => !item.label.startsWith('tw:'))
+    expect(prefixed).toHaveLength(0)
+  },
+})
+
+defineTest({
+  name: 'v4: Variant and utility suggestions hide prefix when it has been typed',
+  fs: {
+    'app.css': css`
+      @import 'tailwindcss' prefix(tw);
+    `,
+  },
+  prepare: async ({ root }) => ({ client: await createClient({ root }) }),
+  handle: async ({ client }) => {
+    let document = await client.open({
+      lang: 'html',
+      text: '<div class="tw:">',
+    })
+
+    // <div class="tw:">
+    //               ^
+    let completion = await document.completions({ line: 0, character: 15 })
+
+    expect(completion?.items.length).toBe(19236)
+
+    // Verify that no variants and utilities have prefixes
+    let prefixed = completion.items.filter((item) => item.label.startsWith('tw:'))
+    expect(prefixed).toHaveLength(0)
+  },
+})
+
 defineTest({
   name: 'v4: Completions show inside class functions in JS/TS files',
   fs: {

packages/tailwindcss-language-service/src/completionProvider.ts

@@ -261,29 +261,25 @@ export function completionsFromClassList(
 
     // TODO: This is a bit of a hack
     if (prefix.length > 0) {
-      // No variants seen: suggest the prefix only
+      // No variants seen:
+      // - suggest the prefix as a variant
+      // - Modify the remaining items to include the prefix in the variant name
       if (existingVariants.length === 0) {
-        items = items.slice(0, 1)
+        items = items.map((item, idx) => {
+          if (idx === 0) return item
 
-        return withDefaults(
-          {
-            isIncomplete: false,
-            items,
-          },
-          {
-            data: {
-              ...(state.completionItemData ?? {}),
-              ...(important ? { important } : {}),
-              variants: existingVariants,
-            },
-            range: replacementRange,
-          },
-          state.editor.capabilities.itemDefaults,
-        )
+          item.label = `${prefix}:${item.label}`
+
+          if (item.textEditText) {
+            item.textEditText = `${prefix}:${item.textEditText}`
+          }
+
+          return item
+        })
       }
 
       // The first variant is not the prefix: don't suggest anything
-      if (existingVariants[0] !== prefix) {
+      if (existingVariants.length > 0 && existingVariants[0] !== prefix) {
         return null
       }
     }
@@ -304,6 +300,10 @@ export function completionsFromClassList(
               documentation = formatColor(color)
             }
 
+            if (prefix.length > 0 && existingVariants.length === 0) {
+              className = `${prefix}:${className}`
+            }
+
             items.push({
               label: className,
               kind,

packages/tailwindcss-language-service/src/util/getVariantsFromClassName.ts

@@ -33,6 +33,12 @@ export function getVariantsFromClassName(
       // NOTE: This should never happen
       if (!state.designSystem) return false
 
+      let prefix = state.designSystem.theme.prefix ?? ''
+
+      if (prefix !== '') {
+        className = `${prefix}:${className}`
+      }
+
       // We don't use `compile()` so there's no overhead from PostCSS
       let compiled = state.designSystem.candidatesToCss([className])