From e5fab7be95684a7ff16f5f14d14313b1765a397f Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 00:32:29 +0200
Subject: [PATCH 1/7] we should mark it as an unsafe migration

We already know we are in v4 and up and it didn't compile. All
migrations will fail but will still run, so now we can bail early.
---
 .../src/codemods/template/is-safe-migration.ts                  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index a344e56ed18f..883098de27c6 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -62,7 +62,7 @@ export function isSafeMigration(
   // So let's only skip if we couldn't parse and we are not in Tailwind CSS v3.
   //
   if (!candidate && version.isGreaterThan(3)) {
-    return true
+    return false
   }
 
   // Parsed a candidate succesfully, verify if it's a valid candidate

From 1c5296837b8b4f2958e0fecbbb9b8842fd2b4f66 Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 00:33:46 +0200
Subject: [PATCH 2/7] fix typo

---
 .../src/codemods/template/is-safe-migration.ts                  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index 883098de27c6..18e7b13e7d46 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -65,7 +65,7 @@ export function isSafeMigration(
     return false
   }
 
-  // Parsed a candidate succesfully, verify if it's a valid candidate
+  // Parsed a candidate successfully, verify if it's a valid candidate
   else if (candidate) {
     // When we have variants, we can assume that the candidate is safe to migrate
     // because that requires colons.

From 56b094c1767d19e38ed1a3a7a83b7fd491d0035e Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 01:04:17 +0200
Subject: [PATCH 3/7] compute `<style>` and `</style>` positions once
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This allows us to compute all the positions once and cache it per file
contents. This is useful because otherwise we have to check the exact
same file over and over and over again, but just for different
positions.

This also just computes the ranges of start and end positions. This will
allow us to simply check if the candidate is between any of 2 pair
points to know if we are in a `<style>…</style>` or not.
---
 .../codemods/template/is-safe-migration.ts    | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index 18e7b13e7d46..96b56d768483 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -1,5 +1,6 @@
 import { parseCandidate } from '../../../../tailwindcss/src/candidate'
 import type { DesignSystem } from '../../../../tailwindcss/src/design-system'
+import { DefaultMap } from '../../../../tailwindcss/src/utils/default-map'
 import * as version from '../../utils/version'
 
 const QUOTES = ['"', "'", '`']
@@ -168,3 +169,30 @@ export function isSafeMigration(
 
   return true
 }
+
+// Assumptions:
+// - All `<style` tags appear before the next `</style>` tag
+// - All `<style` tags are closed with `</style>`
+// - No nested `<style>` tags
+const styleBlockRanges = new DefaultMap((source: string) => {
+  let ranges: number[] = []
+  let offset = 0
+
+  while (true) {
+    let startTag = source.indexOf('<style', offset)
+    if (startTag === -1) return ranges
+
+    // Ensure the style looks like:
+    // - `<style>`   (closed)
+    // - `<style …>` (with attributes)
+    if (!source[startTag + 6].match(/[>\s]/)) return ranges
+
+    offset = startTag + 1
+
+    let endTag = source.indexOf('</style>', offset)
+    if (endTag === -1) return ranges
+    offset = endTag + 1
+
+    ranges.push(startTag, endTag)
+  }
+})

From 7020cc4d98a76ea218118bec6ba77005b5896ada Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 01:06:04 +0200
Subject: [PATCH 4/7] use ranges to compute if we are in a style block

---
 .../codemods/template/is-safe-migration.ts    | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index 96b56d768483..b8b845a7a991 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -45,13 +45,20 @@ export function isSafeMigration(
     // Whitespace before the candidate
     location.contents[location.start - 1]?.match(/\s/) &&
     // A colon followed by whitespace after the candidate
-    location.contents.slice(location.end, location.end + 2)?.match(/^:\s/) &&
-    // A `<style` block is present before the candidate
-    location.contents.slice(0, location.start).includes('<style') &&
-    // `</style>` is present after the candidate
-    location.contents.slice(location.end).includes('</style>')
+    location.contents.slice(location.end, location.end + 2)?.match(/^:\s/)
   ) {
-    return false
+    // Compute all `<style>` ranges once and cache it for the current files
+    let ranges = styleBlockRanges.get(location.contents)
+
+    for (let i = 0; i < ranges.length; i += 2) {
+      let start = ranges[i]
+      let end = ranges[i + 1]
+
+      // Check if the candidate is inside a `<style>` block
+      if (location.start >= start && location.end <= end) {
+        return false
+      }
+    }
   }
 
   let [candidate] = Array.from(parseCandidate(rawCandidate, designSystem))

From 17a7cca4a5deda67b4dc26383c5560fec814db76 Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 01:06:28 +0200
Subject: [PATCH 5/7] optimization: destructure from iterator

There is no need to convert the iterator to an array first. We can just
destructure the first value immediately.
---
 .../src/codemods/template/is-safe-migration.ts                  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index b8b845a7a991..6368c5d09ebc 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -61,7 +61,7 @@ export function isSafeMigration(
     }
   }
 
-  let [candidate] = Array.from(parseCandidate(rawCandidate, designSystem))
+  let [candidate] = parseCandidate(rawCandidate, designSystem)
 
   // If we can't parse the candidate, then it's not a candidate at all. However,
   // we could be dealing with legacy classes like `tw__flex` in Tailwind CSS v3

From 2c1c31ba91798ba1e5829aae30938b1ae314f251 Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Sat, 17 May 2025 01:17:13 +0200
Subject: [PATCH 6/7] update changelog

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f4ab2a1e561c..a5fb9603d04b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
-- Upgrade: Do not migrate declarations that look like candidates in `<style>` blocks ([#18057](https://github.com/tailwindlabs/tailwindcss/pull/18057))
+- Upgrade: Do not migrate declarations that look like candidates in `<style>` blocks ([#18057](https://github.com/tailwindlabs/tailwindcss/pull/18057), [18068](https://github.com/tailwindlabs/tailwindcss/pull/18068))
 - Upgrade: Improve `pnpm` workspaces support ([#18065](https://github.com/tailwindlabs/tailwindcss/pull/18065))
 
 ## [4.1.7] - 2025-05-15

From f1572a48ff4fc7d67b49470926a40f83b82a3091 Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Mon, 19 May 2025 12:24:47 +0200
Subject: [PATCH 7/7] Update
 packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts

Co-authored-by: Jordan Pittman <jordan@cryptica.me>
---
 .../src/codemods/template/is-safe-migration.ts              | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
index 6368c5d09ebc..047424e11291 100644
--- a/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
+++ b/packages/@tailwindcss-upgrade/src/codemods/template/is-safe-migration.ts
@@ -189,12 +189,12 @@ const styleBlockRanges = new DefaultMap((source: string) => {
     let startTag = source.indexOf('<style', offset)
     if (startTag === -1) return ranges
 
+    offset = startTag + 1
+
     // Ensure the style looks like:
     // - `<style>`   (closed)
     // - `<style …>` (with attributes)
-    if (!source[startTag + 6].match(/[>\s]/)) return ranges
-
-    offset = startTag + 1
+    if (!source[startTag + 6].match(/[>\s]/)) continue
 
     let endTag = source.indexOf('</style>', offset)
     if (endTag === -1) return ranges