YAML: correctly serialize infinity and NaN (crystal-lang#9780)

spec/std/yaml/serialization_spec.cr

@@ -72,13 +72,19 @@ describe "YAML serialization" do
 
     it "does Float32#from_yaml" do
       Float32.from_yaml("1.5").should eq(1.5_f32)
+      Float32.from_yaml(".nan").nan?.should be_true
       Float32.from_yaml(".inf").should eq(Float32::INFINITY)
+      Float32.from_yaml("-.inf").should eq(-Float32::INFINITY)
     end
 
     it "does Float64#from_yaml" do
       value = Float64.from_yaml("1.5")
       value.should eq(1.5)
       value.should be_a(Float64)
+
+      Float64.from_yaml(".nan").nan?.should be_true
+      Float64.from_yaml(".inf").should eq(Float64::INFINITY)
+      Float64.from_yaml("-.inf").should eq(-Float64::INFINITY)
     end
 
     it "does Array#from_yaml" do
@@ -276,10 +282,38 @@ describe "YAML serialization" do
       Int32.from_yaml(1.to_yaml).should eq(1)
     end
 
+    it "does for Float32" do
+      Float32.from_yaml(1.5_f32.to_yaml).should eq(1.5_f32)
+    end
+
+    it "does for Float32 (infinity)" do
+      Float32.from_yaml(Float32::INFINITY.to_yaml).should eq(Float32::INFINITY)
+    end
+
+    it "does for Float32 (-infinity)" do
+      Float32.from_yaml((-Float32::INFINITY).to_yaml).should eq(-Float32::INFINITY)
+    end
+
+    it "does for Float32 (nan)" do
+      Float32.from_yaml(Float32::NAN.to_yaml).nan?.should be_true
+    end
+
     it "does for Float64" do
       Float64.from_yaml(1.5.to_yaml).should eq(1.5)
     end
 
+    it "does for Float64 (infinity)" do
+      Float64.from_yaml(Float64::INFINITY.to_yaml).should eq(Float64::INFINITY)
+    end
+
+    it "does for Float64 (-infinity)" do
+      Float64.from_yaml((-Float64::INFINITY).to_yaml).should eq(-Float64::INFINITY)
+    end
+
+    it "does for Float64 (nan)" do
+      Float64.from_yaml(Float64::NAN.to_yaml).nan?.should be_true
+    end
+
     it "does for String" do
       String.from_yaml("hello".to_yaml).should eq("hello")
     end

src/yaml/to_yaml.cr

@@ -80,6 +80,21 @@ struct Number
   end
 end
 
+struct Float
+  def to_yaml(yaml : YAML::Nodes::Builder)
+    infinite = self.infinite?
+    if infinite == 1
+      yaml.scalar(".inf")
+    elsif infinite == -1
+      yaml.scalar("-.inf")
+    elsif nan?
+      yaml.scalar(".nan")
+    else
+      yaml.scalar self.to_s
+    end
+  end
+end
+
 struct Nil
   def to_yaml(yaml : YAML::Nodes::Builder)
     yaml.scalar ""