[XamlC] Compile ContraintTypeConverters (#592)

* [XamlC] Compile ContraintTypeConverters

* fix error message

2 files changed, 29 insertions, 0 deletions

diff --git a/Xamarin.Forms.Build.Tasks/CompiledConverters/ConstraintTypeConverter.cs b/Xamarin.Forms.Build.Tasks/CompiledConverters/ConstraintTypeConverter.cs
new file mode 100644
index 00000000..18b1810c
--- /dev/null
+++ b/Xamarin.Forms.Build.Tasks/CompiledConverters/ConstraintTypeConverter.cs
@@ -0,0 +1,28 @@
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+
+using Mono.Cecil;
+using Mono.Cecil.Cil;
+
+using Xamarin.Forms.Xaml;
+
+namespace Xamarin.Forms.Core.XamlC
+{
+	class ConstraintTypeConverter : ICompiledTypeConverter
+	{
+		public IEnumerable<Instruction> ConvertFromString(string value, ModuleDefinition module, BaseNode node)
+		{
+			double size;
+
+			if (string.IsNullOrEmpty(value) || !double.TryParse(value, NumberStyles.Number, CultureInfo.InvariantCulture, out size))
+				throw new XamlParseException($"Cannot convert \"{value}\" into {typeof(Constraint)}", node);
+
+			yield return Instruction.Create(OpCodes.Ldc_R8, size);
+
+			var constantDef = module.Import(typeof(Constraint)).Resolve().Methods.FirstOrDefault(md => md.IsStatic && md.Name == "Constant");
+			var constantRef = module.Import(constantDef);
+			yield return Instruction.Create(OpCodes.Call, constantRef);
+		}
+	}
+}
diff --git a/Xamarin.Forms.Build.Tasks/Xamarin.Forms.Build.Tasks.csproj b/Xamarin.Forms.Build.Tasks/Xamarin.Forms.Build.Tasks.csproj
index c845b597..9507ea3c 100644
--- a/Xamarin.Forms.Build.Tasks/Xamarin.Forms.Build.Tasks.csproj
+++ b/Xamarin.Forms.Build.Tasks/Xamarin.Forms.Build.Tasks.csproj
@@ -101,6 +101,7 @@
     <Compile Include="Logger.cs" />
     <Compile Include="XamlTask.cs" />
     <Compile Include="CompiledMarkupExtensions\ArrayExtension.cs" />
+    <Compile Include="CompiledConverters\ConstraintTypeConverter.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">