Implement copy-on-write semantics for VarSet, speeding up Environment cloning

spec/rscons/varset_spec.rb

@@ -21,9 +21,9 @@ module Rscons
     end
 
     describe "#[]" do
-      v = VarSet.new({"fuz" => "a string", "foo" => 42, "bar" => :baz,
-                      "qax" => [3, 6], "qux" => {a: :b}})
       it "allows accessing a variable with its verbatim value if type is not specified" do
+        v = VarSet.new({"fuz" => "a string", "foo" => 42, "bar" => :baz,
+                        "qax" => [3, 6], "qux" => {a: :b}})
         v["fuz"].should == "a string"
         v["foo"].should == 42
         v["bar"].should == :baz
@@ -44,11 +44,21 @@ module Rscons
     describe "#include?" do
       it "returns whether the variable is in the VarSet" do
         v = VarSet.new("CFLAGS" => [], :foo => :bar)
+
         expect(v.include?("CFLAGS")).to be_true
         expect(v.include?(:CFLAGS)).to be_false
         expect(v.include?(:foo)).to be_true
         expect(v.include?("foo")).to be_false
         expect(v.include?("bar")).to be_false
+
+        v2 = v.clone
+        v2.append("bar" => [])
+
+        expect(v2.include?("CFLAGS")).to be_true
+        expect(v2.include?(:CFLAGS)).to be_false
+        expect(v2.include?(:foo)).to be_true
+        expect(v2.include?("foo")).to be_false
+        expect(v2.include?("bar")).to be_true
       end
     end
 
@@ -56,14 +66,26 @@ module Rscons
       it "adds values from a Hash to the VarSet" do
         v = VarSet.new("LDFLAGS" => "-lgcc")
         v.append("LIBS" => "gcc", "LIBPATH" => ["mylibs"])
-        v.vars.keys.should =~ ["LDFLAGS", "LIBS", "LIBPATH"]
+        expect(v["LDFLAGS"]).to eq("-lgcc")
+        expect(v["LIBS"]).to eq("gcc")
+        expect(v["LIBPATH"]).to eq(["mylibs"])
       end
+
       it "adds values from another VarSet to the VarSet" do
         v = VarSet.new("CPPPATH" => ["mydir"])
         v2 = VarSet.new("CFLAGS" => ["-O0"], "CPPPATH" => ["different_dir"])
         v.append(v2)
-        v.vars.keys.should =~ ["CPPPATH", "CFLAGS"]
-        v["CPPPATH"].should == ["different_dir"]
+        expect(v["CFLAGS"]).to eq(["-O0"])
+        expect(v["CPPPATH"]).to eq(["different_dir"])
+      end
+
+      it "does not pick up subsequent variable changes from a given VarSet" do
+        v = VarSet.new("dirs" => ["a"])
+        v2 = VarSet.new
+        v2.append(v)
+        v["dirs"] << "b"
+        expect(v["dirs"]).to eq(["a", "b"])
+        expect(v2["dirs"]).to eq(["a"])
       end
     end
 
@@ -71,17 +93,30 @@ module Rscons
       it "returns a new VarSet merged with the given Hash" do
         v = VarSet.new("foo" => "yoda")
         v2 = v.merge("baz" => "qux")
-        v.vars.keys.should == ["foo"]
-        v2.vars.keys.should =~ ["foo", "baz"]
+        expect(v["foo"]).to eq("yoda")
+        expect(v2["foo"]).to eq("yoda")
+        expect(v2["baz"]).to eq("qux")
       end
+
       it "returns a new VarSet merged with the given VarSet" do
         v = VarSet.new("foo" => ["a", "b"], "bar" => 42)
         v2 = v.merge(VarSet.new("bar" => 33, "baz" => :baz))
         v2["foo"] << "c"
-        v["foo"].should == ["a", "b"]
-        v["bar"].should == 42
-        v2["foo"].should == ["a", "b", "c"]
-        v2["bar"].should == 33
+        expect(v["foo"]).to eq ["a", "b"]
+        expect(v["bar"]).to eq 42
+        expect(v2["foo"]).to eq ["a", "b", "c"]
+        expect(v2["bar"]).to eq 33
+      end
+
+      it "does not pick up subsequent variable changes from a given VarSet" do
+        v = VarSet.new("var" => ["a", "b"], "var2" => ["1", "2"])
+        v["var2"] << "3"
+        v2 = v.clone
+        v["var"] << "c"
+        expect(v["var"]).to eq(["a", "b", "c"])
+        expect(v["var2"]).to eq(["1", "2", "3"])
+        expect(v2["var"]).to eq(["a", "b"])
+        expect(v2["var2"]).to eq(["1", "2", "3"])
       end
     end