From eae9ec15884b3f02ee86ec62a07fc69e1a0355fc Mon Sep 17 00:00:00 2001
From: Daniel Cazzulino <daniel@cazzulino.com>
Date: Thu, 26 Sep 2024 23:27:51 -0300
Subject: [PATCH] Add support for typed constants

Fixes #150
---
 src/ThisAssembly.Constants/CSharp.sbntxt      | 10 ++++-
 .../ConstantsGenerator.cs                     |  9 ++--
 src/ThisAssembly.Constants/Model.cs           |  5 ++-
 .../ThisAssembly.Constants.targets            |  1 +
 src/ThisAssembly.Constants/readme.md          | 41 ++++++++++++++++++-
 src/ThisAssembly.Tests/Tests.cs               | 20 +++++++++
 .../ThisAssembly.Tests.csproj                 |  5 +++
 7 files changed, 83 insertions(+), 8 deletions(-)

diff --git a/src/ThisAssembly.Constants/CSharp.sbntxt b/src/ThisAssembly.Constants/CSharp.sbntxt
index 98cd71d7..f9c0ab07 100644
--- a/src/ThisAssembly.Constants/CSharp.sbntxt
+++ b/src/ThisAssembly.Constants/CSharp.sbntxt
@@ -40,13 +40,19 @@
         {{- summary value -}}
         {{- remarks -}}
         {{ obsolete }}
-        {{~ if RawStrings ~}}
+        {{~ if RawStrings && value.IsText ~}}
 	    public const string {{ value.Name | string.replace "-" "_" | string.replace " " "_" }} = 
+
 """
 {{ value.Value }}
 """;
         {{~ else ~}}
-	    public const string {{ value.Name | string.replace "-" "_" | string.replace " " "_" }} = @"{{ value.Value }}";
+	    public const {{ value.Type }} {{ value.Name | string.replace "-" "_" | string.replace " " "_" }} = 
+            {{~ if value.IsText ~}}
+            @"{{ value.Value }}";
+            {{~ else ~}}
+            {{ value.Value }};
+            {{~ end ~}}
         {{~ end ~}}
         {{~ end ~}}
 
diff --git a/src/ThisAssembly.Constants/ConstantsGenerator.cs b/src/ThisAssembly.Constants/ConstantsGenerator.cs
index eb6e8cfc..0d040753 100644
--- a/src/ThisAssembly.Constants/ConstantsGenerator.cs
+++ b/src/ThisAssembly.Constants/ConstantsGenerator.cs
@@ -26,6 +26,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
             .Select((x, ct) =>
             {
                 x.Right.GetOptions(x.Left).TryGetValue("build_metadata.Constant.Value", out var value);
+                x.Right.GetOptions(x.Left).TryGetValue("build_metadata.Constant.Type", out var type);
                 x.Right.GetOptions(x.Left).TryGetValue("build_metadata.Constant.Comment", out var comment);
                 x.Right.GetOptions(x.Left).TryGetValue("build_metadata.Constant.Root", out var root);
 
@@ -52,7 +53,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                     }
                 }
 
-                return (name, value: value ?? "", comment: string.IsNullOrWhiteSpace(comment) ? null : comment, root!);
+                return (name, value: value ?? "", type: string.IsNullOrWhiteSpace(type) ? null : type, comment: string.IsNullOrWhiteSpace(comment) ? null : comment, root!);
             });
 
         // Read the ThisAssemblyNamespace property or default to null
@@ -68,9 +69,9 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
     }
 
     void GenerateConstant(SourceProductionContext spc,
-        (((string name, string value, string? comment, string root), (string? ns, ParseOptions parse)), StatusOptions options) args)
+        (((string name, string value, string? type, string? comment, string root), (string? ns, ParseOptions parse)), StatusOptions options) args)
     {
-        var (((name, value, comment, root), (ns, parse)), options) = args;
+        var (((name, value, type, comment, root), (ns, parse)), options) = args;
         var cs = (CSharpParseOptions)parse;
 
         if (!string.IsNullOrWhiteSpace(ns) &&
@@ -89,7 +90,7 @@ void GenerateConstant(SourceProductionContext spc,
             comment = "/// " + string.Join(Environment.NewLine + "/// ", value.Replace("\\n", Environment.NewLine).Trim(['\r', '\n']).Split([Environment.NewLine], StringSplitOptions.None));
 
         // Revert normalization of newlines performed in MSBuild to workaround the limitation in editorconfig.
-        var rootArea = Area.Load([new(name, value.Replace("\\n", Environment.NewLine).Trim(['\r', '\n']), comment),], root);
+        var rootArea = Area.Load([new(name, value.Replace("\\n", Environment.NewLine).Trim(['\r', '\n']), comment, type ?? "string"),], root);
         // For now, we only support C# though
         var file = parse.Language.Replace("#", "Sharp") + ".sbntxt";
         var template = Template.Parse(EmbeddedResource.GetContent(file), file);
diff --git a/src/ThisAssembly.Constants/Model.cs b/src/ThisAssembly.Constants/Model.cs
index 9e7f3cde..ed736678 100644
--- a/src/ThisAssembly.Constants/Model.cs
+++ b/src/ThisAssembly.Constants/Model.cs
@@ -105,4 +105,7 @@ static Area GetArea(Area area, IEnumerable<string> areaPath)
 }
 
 [DebuggerDisplay("{Name} = {Value}")]
-record Constant(string Name, string? Value, string? Comment);
+record Constant(string Name, string? Value, string? Comment, string Type = "string")
+{
+    public bool IsText => Type.Equals("string", StringComparison.OrdinalIgnoreCase);
+}
diff --git a/src/ThisAssembly.Constants/ThisAssembly.Constants.targets b/src/ThisAssembly.Constants/ThisAssembly.Constants.targets
index 0ecb711f..5e0f167b 100644
--- a/src/ThisAssembly.Constants/ThisAssembly.Constants.targets
+++ b/src/ThisAssembly.Constants/ThisAssembly.Constants.targets
@@ -7,6 +7,7 @@
     <CompilerVisibleItemMetadata Include="Constant" MetadataName="ItemType" />
     <CompilerVisibleItemMetadata Include="Constant" MetadataName="Comment" />
     <CompilerVisibleItemMetadata Include="Constant" MetadataName="Value" />
+    <CompilerVisibleItemMetadata Include="Constant" MetadataName="Type" />
     <CompilerVisibleItemMetadata Include="Constant" MetadataName="Root" />
 
     <!-- Make sure we're always private to the referencing project. 
diff --git a/src/ThisAssembly.Constants/readme.md b/src/ThisAssembly.Constants/readme.md
index 53289c83..b251e2c9 100644
--- a/src/ThisAssembly.Constants/readme.md
+++ b/src/ThisAssembly.Constants/readme.md
@@ -10,9 +10,48 @@ constants for `@(Constant)` MSBuild items in the project.
   </ItemGroup>
 ```
 
-
 ![](https://raw.githubusercontent.com/devlooped/ThisAssembly/main/img/ThisAssembly.Constants.png)
 
+These constants can use values from MSBuild properties, making compile-time values configurable 
+via environment variables or command line arguments. For example:
+
+```xml
+  <PropertyGroup>
+    <HttpDefaultTimeoutSeconds>10</HttpDefaultTimeoutSeconds>
+  </PropertyGroup>
+  <ItemGroup>
+    <Constant Include="Http.TimeoutSeconds" 
+              Value="$(HttpDefaultTimeoutSeconds)" 
+              Type="int" 
+              Comment="Default timeout in seconds for HTTP requests" />
+  </ItemGroup>
+```
+
+The C# code could consume this constant as follows:
+
+```csharp
+
+public HttpClient CreateHttpClient(string name, int? timeout = default)
+{
+    HttpClient client = httpClientFactory.CreateClient(name);
+    client.Timeout = TimeSpan.FromSeconds(timeout ?? ThisAssembly.Constants.Http.TimeoutSeconds);
+    return client;
+}
+```
+
+Note how the constant is typed to `int` as specified in the `Type` attribute in MSBuild. 
+The generated code uses the specified `Type` as-is, as well as the `Value` attribute in that 
+case, so it's up to the user to ensure they match and result in valid C# code. For example, 
+you can emit a boolean, long, double, etc., but a `DateTime` wouldn't be a valid constant even 
+if you set the `Value` to `DateTime.Now`. If no type is provided, `string` is assumed. Values 
+can also be multi-line and will use [C# raw string literals](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/raw-string) 
+if supported by the target language version (11+).
+
+In this example, you could trivially change how your product behaves by setting the environment 
+variable `HttpDefaultTimeoutSeconds` in CI. This is particularly useful for test projects, 
+where you can easily change the behavior of the system under test without changing the code.
+
+
 In addition to arbitrary constants via `<Constant ...>`, it's quite useful (in particular in test projects) 
 to generate constants for files in the project, so there's also a shorthand for those:
 
diff --git a/src/ThisAssembly.Tests/Tests.cs b/src/ThisAssembly.Tests/Tests.cs
index 7b35bfcb..0e227a0d 100644
--- a/src/ThisAssembly.Tests/Tests.cs
+++ b/src/ThisAssembly.Tests/Tests.cs
@@ -43,6 +43,26 @@ with a newline and
     public void CanUseConstants()
         => Assert.Equal("Baz", ThisAssembly.Constants.Foo.Bar);
 
+    [Fact]
+    public void CanUseTypedIntConstant()
+        => Assert.Equal(123, ThisAssembly.Constants.TypedInt);
+
+    [Fact]
+    public void CanUseTypedInt64Constant()
+        => Assert.Equal(123, ThisAssembly.Constants.TypedInt64);
+
+    [Fact]
+    public void CanUseTypedLongConstant()
+        => Assert.Equal(123, ThisAssembly.Constants.TypedLong);
+
+    [Fact]
+    public void CanUseTypedBoolConstant()
+        => Assert.True(ThisAssembly.Constants.TypedBoolean);
+
+    [Fact]
+    public void CanUseTypedDoubleConstant()
+        => Assert.Equal(1.23, ThisAssembly.Constants.TypedDouble);
+
     [Fact]
     public void CanUseFileConstants()
         => Assert.Equal(ThisAssembly.Constants.Content.Docs.License, Path.Combine("Content", "Docs", "License.md"));
diff --git a/src/ThisAssembly.Tests/ThisAssembly.Tests.csproj b/src/ThisAssembly.Tests/ThisAssembly.Tests.csproj
index aeefda82..1d5d29a5 100644
--- a/src/ThisAssembly.Tests/ThisAssembly.Tests.csproj
+++ b/src/ThisAssembly.Tests/ThisAssembly.Tests.csproj
@@ -76,6 +76,11 @@
     <AssemblyMetadata Include="Foo" Value="Bar" />
     <AssemblyMetadata Include="Raw" Value="$(Multiline)" />
     <AssemblyMetadata Include="Root.Foo.Bar" Value="Baz" Comment="Comment" />
+    <Constant Include="TypedInt" Value="123" Type="int" />
+    <Constant Include="TypedInt64" Value="123" Type="Int64" />
+    <Constant Include="TypedLong" Value="123" Type="long" />
+    <Constant Include="TypedDouble" Value="1.23" Type="double" />
+    <Constant Include="TypedBoolean" Value="true" Type="bool" />
   </ItemGroup>
 
   <ItemGroup>