From fb15852f41ee77dc12c0d0df96c10fe17b5c597f Mon Sep 17 00:00:00 2001
From: xzyfer <xzyfer@gmail.com>
Date: Sat, 24 Mar 2018 13:24:12 +1100
Subject: [PATCH] Add a deprecation warning for @import's that resolved .css
 files

This is the first to removing native CSS imports.

Like Ruby Sass, Dart Sass will not implement this behaviour. This is
blocking compatibility between Node Sass and Dart Sass.

This is a non-standard behaviour which is constant source of confusion.

We had originally planned to removed this behaviour when the module
system was ready. However that has feature has been delayed and
people are continuing to be tripped up by this behaviour.
---
 src/context.cpp | 8 ++++++++
 src/file.cpp    | 4 ++--
 src/file.hpp    | 7 ++++++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/context.cpp b/src/context.cpp
index e2cffd1db1..46efc05d8e 100644
--- a/src/context.cpp
+++ b/src/context.cpp
@@ -373,6 +373,14 @@ namespace Sass {
     // process the resolved entry
     else if (resolved.size() == 1) {
       bool use_cache = c_importers.size() == 0;
+      if (resolved[0].deprecated) {
+        // emit deprecation warning when import resolves to a .css file
+        deprecated(
+          "Including .css files with @import is non-standard behaviour which will be removed in future versions of LibSass.",
+          "Use a custom importer to maintain this behaviour. Check your implementations documentation on how to create a custom importer.",
+          true, pstate
+        );
+      }
       // use cache for the resource loading
       if (use_cache && sheets.count(resolved[0].abs_path)) return resolved[0];
       // try to read the content of the resolved file entry
diff --git a/src/file.cpp b/src/file.cpp
index 826c8113ce..b40067649b 100644
--- a/src/file.cpp
+++ b/src/file.cpp
@@ -357,13 +357,13 @@ namespace Sass {
       for(auto ext : d_exts) {
         rel_path = join_paths(base, "_" + name + ext);
         abs_path = join_paths(root, rel_path);
-        if (file_exists(abs_path)) includes.push_back({{ rel_path, root }, abs_path });
+        if (file_exists(abs_path)) includes.push_back({{ rel_path, root }, abs_path, true });
       }
       // next test plain name with d_exts
       for(auto ext : d_exts) {
         rel_path = join_paths(base, name + ext);
         abs_path = join_paths(root, rel_path);
-        if (file_exists(abs_path)) includes.push_back({{ rel_path, root }, abs_path });
+        if (file_exists(abs_path)) includes.push_back({{ rel_path, root }, abs_path, true });
       }
       // index files
       if (includes.size() == 0) {
diff --git a/src/file.hpp b/src/file.hpp
index 759996fa85..718a529cd1 100644
--- a/src/file.hpp
+++ b/src/file.hpp
@@ -89,9 +89,14 @@ namespace Sass {
     public:
       // resolved absolute path
       std::string abs_path;
+      // is a deprecated file type
+      bool deprecated;
     public:
+      Include(const Importer& imp, std::string abs_path, bool deprecated)
+      : Importer(imp), abs_path(abs_path), deprecated(deprecated)
+      { }
       Include(const Importer& imp, std::string abs_path)
-      : Importer(imp), abs_path(abs_path)
+      : Importer(imp), abs_path(abs_path), deprecated(false)
       { }
   };