Recognize case-insensitive import and layer at-rule names

lib/parse-statements.js

@@ -14,12 +14,12 @@ module.exports = function parseStatements(result, styles, conditions, from) {
   styles.each(node => {
     let stmt
     if (node.type === "atrule") {
-      if (node.name === "import")
+      if (node.name.toLowerCase() === "import")
         stmt = parseImport(result, node, conditions, from)
       else if (node.name === "charset")
         stmt = parseCharset(result, node, conditions, from)
       else if (
-        node.name === "layer" &&
+        node.name.toLowerCase() === "layer" &&
         !encounteredNonImportNodes &&
         !node.nodes
       )
@@ -78,7 +78,7 @@ function parseImport(result, atRule, conditions, from) {
     do {
       if (
         prev.type === "comment" ||
-        (prev.type === "atrule" && prev.name === "import")
+        (prev.type === "atrule" && prev.name.toLowerCase() === "import")
       ) {
         prev = prev.prev()
         continue
@@ -95,7 +95,8 @@ function parseImport(result, atRule, conditions, from) {
       if (
         prev.type === "comment" ||
         (prev.type === "atrule" &&
-          (prev.name === "charset" || (prev.name === "layer" && !prev.nodes)))
+          (prev.name === "charset" ||
+            (prev.name.toLowerCase() === "layer" && !prev.nodes)))
       ) {
         prev = prev.prev()
         continue

test/at-rule-case.js

@@ -0,0 +1,27 @@
+"use strict"
+
+const path = require("path")
+const { default: test } = require("ava")
+const postcss = require("postcss")
+const atImport = require("..")
+
+for (const input of [
+  '@IMPORT "a.css";',
+  '@ImPoRt "a.css"; @import "b.css";',
+  '@LAYER base; @IMPORT "a.css";',
+]) {
+  test(`should recognize case-insensitive at-rule names: ${input}`, async t => {
+    const result = await postcss([
+      atImport({
+        resolve: id => path.resolve(id),
+        load: () => "a { color: red; }",
+      }),
+    ]).process(input, { from: undefined })
+
+    t.is(result.warnings().length, 0)
+    t.false(/@import/i.test(result.css))
+    t.true(result.css.includes("color: red"))
+    if (input.startsWith("@LAYER"))
+      t.true(result.css.startsWith("@LAYER base;"))
+  })
+}

test/lint.js

@@ -8,6 +8,21 @@ const atImport = require("..")
 
 const processor = postcss().use(atImport())
 
+test("should warn if uppercase @CHARSET before @import", async t => {
+  const result = await processor.process(
+    '@CHARSET "utf-8"; @IMPORT "test/fixtures/imports/foo.css";',
+    {
+      from: undefined,
+    },
+  )
+  const warnings = result.warnings()
+  t.is(warnings.length, 1)
+  t.is(
+    warnings[0].text,
+    "@import statements must precede all other statements (besides @charset or empty @layer) and be consecutive",
+  )
+})
+
 test("should warn when not @charset and not @import statement before", t => {
   return Promise.all([
     processor.process(`a {} @import "";`, { from: undefined }),