Background and Motivation

The first-class Span types feature is adding new span conversions. For consistency with other conversions, it would be good to have the API proposed below.

Proposed API

 namespace Microsoft.CodeAnalysis.CSharp;
 public readonly struct Conversion
 {
+    public bool IsSpan { get; }
 }

Usage Examples

var comp = new CSharpCompilation(...);
var tree = comp.SyntaxTrees.Single();
var model = comp.GetSemanticModel(tree);
var expr = tree.GetRoot().DescendantNodes()...;
var conversion = model.GetConversion(expr);
Assert.True(conversion.IsSpan); // used here

Alternative Designs

• Leave the API internal.
• Provide details about which span conversion it is (array to Span/ReadOnlySpan, Span to ReadOnlySpan, ReadOnlySpan to ReadOnlySpan, string to ReadOnlySpan).
• Provide details about the methods that will be used in codegen.

Risks

• We might remove the feature and then the API will be useless?