Make same-file duplicate skipping the default, fixes #601

README.md

@@ -180,13 +180,18 @@ promised content.
 
 #### `skipDuplicates`
 
-Type: `Boolean`  
+Type: `Boolean` or `"content"`  
 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.
+By default, repeated imports of the same file are being skipped.
+
+Set this option to `"content"` to skip similar files based on their content
+instead, so that copies of the same stylesheet (`normalize.css` for example)
+imported from different paths are also skipped. Files can contain at-rules
+whose paths resolve relative to the file's own location, which is why this
+is not the default.
+
+If you don't want any duplicates to be skipped, set this option to `false`.
 
 #### `addModulesDirectories`
 

lib/parse-styles.js

@@ -179,7 +179,7 @@ async function loadImportContent(
 
   // skip previous imported files not containing @import rules
   if (
-    options.skipDuplicates &&
+    options.skipDuplicates === "content" &&
     state.hashFiles[content]?.[stmtDuplicateCheckKey]
   ) {
     return
@@ -196,7 +196,7 @@ async function loadImportContent(
   const styles = importedResult.root
   result.messages = result.messages.concat(importedResult.messages)
 
-  if (options.skipDuplicates) {
+  if (options.skipDuplicates === "content") {
     const hasImport = styles.some(child => {
       return child.type === "atrule" && child.name === "import"
     })

test/fixtures/content-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/content-dedup.expected.css

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

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 +46,21 @@ test(
 
 test("should import stylesheets with same content", checkFixture, "same")
 
+test(
+  "should not skip different files with the same content by default",
+  checkFixture,
+  "same-file-dedup",
+)
+
+test(
+  "should skip files with the same content with skipDuplicates: content",
+  checkFixture,
+  "content-dedup",
+  {
+    skipDuplicates: "content",
+  },
+)
+
 test("should ignore & adjust external import", checkFixture, "ignore")
 
 test("should not fail with only one absolute import", t => {