From 6febfd966a4c2c5f16a5301dfb86e619ab1f19cd Mon Sep 17 00:00:00 2001
From: Jordan Pittman <jordan@cryptica.me>
Date: Wed, 16 Apr 2025 17:48:26 -0400
Subject: [PATCH] Track locations when printing

---
 packages/tailwindcss/src/ast.bench.ts |  28 ++++++
 packages/tailwindcss/src/ast.ts       | 140 +++++++++++++++++++++++++-
 packages/tailwindcss/src/index.ts     |   2 +-
 3 files changed, 168 insertions(+), 2 deletions(-)
 create mode 100644 packages/tailwindcss/src/ast.bench.ts

diff --git a/packages/tailwindcss/src/ast.bench.ts b/packages/tailwindcss/src/ast.bench.ts
new file mode 100644
index 000000000..a2d8b2892
--- /dev/null
+++ b/packages/tailwindcss/src/ast.bench.ts
@@ -0,0 +1,28 @@
+import { bench } from 'vitest'
+import { toCss } from './ast'
+import * as CSS from './css-parser'
+
+const css = String.raw
+const input = css`
+  @theme {
+    --color-primary: #333;
+  }
+  @tailwind utilities;
+  .foo {
+    color: red;
+    /* comment */
+    &:hover {
+      color: blue;
+      @apply font-bold;
+    }
+  }
+`
+const ast = CSS.parse(input)
+
+bench('toCss', () => {
+  toCss(ast)
+})
+
+bench('toCss with source maps', () => {
+  toCss(ast, true)
+})
diff --git a/packages/tailwindcss/src/ast.ts b/packages/tailwindcss/src/ast.ts
index a3f1835b0..e4b5d5a9a 100644
--- a/packages/tailwindcss/src/ast.ts
+++ b/packages/tailwindcss/src/ast.ts
@@ -714,7 +714,14 @@ export function optimizeAst(
   return newAst
 }
 
-export function toCss(ast: AstNode[]) {
+export function toCss(ast: AstNode[], track?: boolean) {
+  let pos = 0
+
+  let source: Source = {
+    file: null,
+    code: '',
+  }
+
   function stringify(node: AstNode, depth = 0): string {
     let css = ''
     let indent = '  '.repeat(depth)
@@ -722,15 +729,70 @@ export function toCss(ast: AstNode[]) {
     // Declaration
     if (node.kind === 'declaration') {
       css += `${indent}${node.property}: ${node.value}${node.important ? ' !important' : ''};\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // node.property
+        let start = pos
+        pos += node.property.length
+
+        // `: `
+        pos += 2
+
+        // node.value
+        pos += node.value?.length ?? 0
+
+        // !important
+        if (node.important) {
+          pos += 11
+        }
+
+        let end = pos
+
+        // `;\n`
+        pos += 2
+
+        node.dst = [source, start, end]
+      }
     }
 
     // Rule
     else if (node.kind === 'rule') {
       css += `${indent}${node.selector} {\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // node.selector
+        let start = pos
+        pos += node.selector.length
+
+        // ` `
+        pos += 1
+
+        let end = pos
+        node.dst = [source, start, end]
+
+        // `{\n`
+        pos += 2
+      }
+
       for (let child of node.nodes) {
         css += stringify(child, depth + 1)
       }
+
       css += `${indent}}\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // `}\n`
+        pos += 2
+      }
     }
 
     // AtRule
@@ -744,19 +806,93 @@ export function toCss(ast: AstNode[]) {
       // ```
       if (node.nodes.length === 0) {
         let css = `${indent}${node.name} ${node.params};\n`
+
+        if (track) {
+          // indent
+          pos += indent.length
+
+          // node.name
+          let start = pos
+          pos += node.name.length
+
+          // ` `
+          pos += 1
+
+          // node.params
+          pos += node.params.length
+          let end = pos
+
+          // `;\n`
+          pos += 2
+
+          node.dst = [source, start, end]
+        }
+
         return css
       }
 
       css += `${indent}${node.name}${node.params ? ` ${node.params} ` : ' '}{\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // node.name
+        let start = pos
+        pos += node.name.length
+
+        if (node.params) {
+          // ` `
+          pos += 1
+
+          // node.params
+          pos += node.params.length
+        }
+
+        // ` `
+        pos += 1
+
+        let end = pos
+        node.dst = [source, start, end]
+
+        // `{\n`
+        pos += 2
+      }
+
       for (let child of node.nodes) {
         css += stringify(child, depth + 1)
       }
+
       css += `${indent}}\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // `}\n`
+        pos += 2
+      }
     }
 
     // Comment
     else if (node.kind === 'comment') {
       css += `${indent}/*${node.value}*/\n`
+
+      if (track) {
+        // indent
+        pos += indent.length
+
+        // The comment itself. We do this instead of just the inside because
+        // it seems more useful to have the entire comment span tracked.
+        let start = pos
+        pos += 2 + node.value.length + 2
+        let end = pos
+
+        node.dst = [source, start, end]
+
+        // `\n`
+        pos += 1
+      }
     }
 
     // These should've been handled already by `optimizeAst` which
@@ -780,6 +916,8 @@ export function toCss(ast: AstNode[]) {
     css += stringify(node, 0)
   }
 
+  source.code = css
+
   return css
 }
 
diff --git a/packages/tailwindcss/src/index.ts b/packages/tailwindcss/src/index.ts
index 04a99b927..b109713ee 100644
--- a/packages/tailwindcss/src/index.ts
+++ b/packages/tailwindcss/src/index.ts
@@ -814,7 +814,7 @@ export async function compile(
         return compiledCss
       }
 
-      compiledCss = toCss(newAst)
+      compiledCss = toCss(newAst, !!opts.from)
       compiledAst = newAst
 
       return compiledCss