From afc39509537293a2c135fece0eece6b2e8c95ce5 Mon Sep 17 00:00:00 2001
From: awjin <awjinahn@gmail.com>
Date: Thu, 26 Dec 2019 13:02:46 -0800
Subject: [PATCH] Add built-in variables e and pi.

See https://github.com/sass/sass-spec/pull/1501
---
 CHANGELOG.md                 |  2 ++
 lib/src/functions/math.dart  |  5 ++++-
 lib/src/module/built_in.dart | 15 +++++++++++----
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a47dc2b31..a1283ad33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@
   * `hypot()`: given *n* numbers, outputs the length of the *n*-dimensional
     vector that has components equal to each of the inputs.
 
+* Add the variables `pi` and `e` to the built-in "sass:math" module.
+
 ## 1.24.0
 
 * Add an optional `with` clause to the `@forward` rule. This works like the
diff --git a/lib/src/functions/math.dart b/lib/src/functions/math.dart
index e0a106183..84d81ff9c 100644
--- a/lib/src/functions/math.dart
+++ b/lib/src/functions/math.dart
@@ -25,7 +25,10 @@ final global = UnmodifiableListView([
 final module = BuiltInModule("math", functions: [
   _abs, _ceil, _clamp, _compatible, _floor, _hypot, _isUnitless, _max, _min, //
   _percentage, _randomFunction, _round, _unit,
-]);
+], variables: {
+  "e": SassNumber(math.e),
+  "pi": SassNumber(math.pi),
+});
 
 /// Returns a [Callable] named [name] that transforms a number's value
 /// using [transform] and preserves its units.
diff --git a/lib/src/module/built_in.dart b/lib/src/module/built_in.dart
index 63d098687..f1a1f50eb 100644
--- a/lib/src/module/built_in.dart
+++ b/lib/src/module/built_in.dart
@@ -17,19 +17,21 @@ class BuiltInModule<T extends AsyncCallable> implements Module<T> {
   final Uri url;
   final Map<String, T> functions;
   final Map<String, T> mixins;
+  final Map<String, Value> variables;
 
   List<Module<T>> get upstream => const [];
-  Map<String, Value> get variables => const {};
   Map<String, AstNode> get variableNodes => const {};
   Extender get extender => Extender.empty;
   CssStylesheet get css => CssStylesheet.empty(url: url);
   bool get transitivelyContainsCss => false;
   bool get transitivelyContainsExtensions => false;
 
-  BuiltInModule(String name, {Iterable<T> functions, Iterable<T> mixins})
+  BuiltInModule(String name,
+      {Iterable<T> functions, Iterable<T> mixins, Map<String, Value> variables})
       : url = Uri(scheme: "sass", path: name),
         functions = _callableMap(functions),
-        mixins = _callableMap(mixins);
+        mixins = _callableMap(mixins),
+        variables = _variableMap(variables);
 
   /// Returns a map from [callables]' names to their values.
   static Map<String, T> _callableMap<T extends AsyncCallable>(
@@ -39,8 +41,13 @@ class BuiltInModule<T extends AsyncCallable> implements Module<T> {
           : UnmodifiableMapView(
               {for (var callable in callables) callable.name: callable}));
 
+  /// Returns a map from [variables]' names to their values.
+  static Map<String, V> _variableMap<V>(Map<String, V> variables) =>
+      UnmodifiableMapView(
+          variables == null ? {} : UnmodifiableMapView(variables));
+
   void setVariable(String name, Value value, AstNode nodeWithSpan) {
-    throw SassScriptException("Undefined variable.");
+    throw SassScriptException("Cannot modify built-in variable \$$name.");
   }
 
   Module<T> cloneCss() => this;