Allow skipping only same-file duplicates with skipDuplicates: "same-file", fixes #601

README.md

@@ -180,14 +180,19 @@ promised content.
 
 #### `skipDuplicates`
 
-Type: `Boolean`  
+Type: `Boolean` or `"same-file"`  
 Default: `true`
 
 By default, similar files (based on the same content) are being skipped.
 It's to optimize output and skip similar files like `normalize.css` for example.
 If this behavior is not what you want, just set this option to `false` to
 disable it.
 
+Setting this option to `"same-file"` skips repeated imports of the same file,
+but not different files sharing the same content. Use it when imported files
+contain at-rules whose paths resolve relative to the file's own location, so
+that byte-identical files at different paths are not actually duplicates.
+
 #### `addModulesDirectories`
 
 Type: `Array`  

lib/parse-styles.js

@@ -178,8 +178,9 @@ async function loadImportContent(
   }
 
   // skip previous imported files not containing @import rules
+  // (content dedup does not apply in "same-file" mode)
   if (
-    options.skipDuplicates &&
+    options.skipDuplicates === true &&
     state.hashFiles[content]?.[stmtDuplicateCheckKey]
   ) {
     return
@@ -196,7 +197,7 @@ async function loadImportContent(
   const styles = importedResult.root
   result.messages = result.messages.concat(importedResult.messages)
 
-  if (options.skipDuplicates) {
+  if (options.skipDuplicates === true) {
     const hasImport = styles.some(child => {
       return child.type === "atrule" && child.name === "import"
     })

test/fixtures/imports/same-file-dedup/a/shared.css

@@ -0,0 +1 @@
+shared {}

test/fixtures/imports/same-file-dedup/b/shared.css

@@ -0,0 +1 @@
+shared {}

test/fixtures/same-file-dedup.css

@@ -0,0 +1,3 @@
+@import "same-file-dedup/a/shared.css";
+@import "same-file-dedup/b/shared.css";
+@import "same-file-dedup/a/shared.css";

test/fixtures/same-file-dedup.expected.css

@@ -0,0 +1,2 @@
+shared {}
+shared {}

test/import.js

@@ -46,6 +46,15 @@ test(
 
 test("should import stylesheets with same content", checkFixture, "same")
 
+test(
+  "should only skip same-file duplicates with skipDuplicates: same-file",
+  checkFixture,
+  "same-file-dedup",
+  {
+    skipDuplicates: "same-file",
+  },
+)
+
 test("should ignore & adjust external import", checkFixture, "ignore")
 
 test("should not fail with only one absolute import", t => {