Suggest APIs for NativeMethods.txt when no match is found in the metadata

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -759,6 +759,38 @@ public bool TryGenerateConstant(string name)
             return false;
         }
 
+        /// <summary>
+        /// Produces a sequence of suggested APIs with a similar name to the specified one.
+        /// </summary>
+        /// <param name="name">The user-supplied name.</param>
+        /// <returns>A sequence of API names.</returns>
+        public IEnumerable<string> GetSuggestions(string name)
+        {
+            if (name is null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            // Trim suffixes off the name.
+            var suffixes = new List<string> { "A", "W", "32", "64", "Ex" };
+            foreach (string suffix in suffixes)
+            {
+                if (name.EndsWith(suffix, StringComparison.Ordinal))
+                {
+                    name = name.Substring(0, name.Length - suffix.Length);
+                }
+            }
+
+            // We should match on any API for which the given string is a substring.
+            foreach (string candidate in this.fieldsByName.Keys.Concat(this.typesByName.Keys).Concat(this.methodsByName.Keys))
+            {
+                if (candidate.Contains(name))
+                {
+                    yield return candidate;
+                }
+            }
+        }
+
         /// <summary>
         /// Collects the result of code generation.
         /// </summary>

src/Microsoft.Windows.CsWin32/SourceGenerator.cs

@@ -31,6 +31,14 @@ public class SourceGenerator : ISourceGenerator
             DiagnosticSeverity.Warning,
             isEnabledByDefault: true);
 
+        private static readonly DiagnosticDescriptor NoMatchingMethodOrTypeWithSuggestions = new DiagnosticDescriptor(
+            "PInvoke001",
+            "No matching method or type found",
+            "Method or type \"{0}\" not found. Did you mean {1}?",
+            "Functionality",
+            DiagnosticSeverity.Warning,
+            isEnabledByDefault: true);
+
         private static readonly DiagnosticDescriptor NoMethodsForModule = new DiagnosticDescriptor(
             "PInvoke001",
             "No module found",
@@ -152,12 +160,12 @@ public void Execute(GeneratorExecutionContext context)
                         context.ReportDiagnostic(Diagnostic.Create(UseEnumValueDeclaringType, location, declaringEnum));
                         if (!generator.TryGenerate(declaringEnum, context.CancellationToken))
                         {
-                            context.ReportDiagnostic(Diagnostic.Create(NoMatchingMethodOrType, location, declaringEnum));
+                            ReportNoMatch(location, declaringEnum);
                         }
                     }
                     else
                     {
-                        context.ReportDiagnostic(Diagnostic.Create(NoMatchingMethodOrType, location, name));
+                        ReportNoMatch(location, name);
                     }
                 }
             }
@@ -167,6 +175,32 @@ public void Execute(GeneratorExecutionContext context)
             {
                 context.AddSource(unit.Key, unit.Value.ToFullString());
             }
+
+            void ReportNoMatch(Location? location, string failedAttempt)
+            {
+                var suggestions = generator.GetSuggestions(failedAttempt).Take(4).ToList();
+                if (suggestions.Count > 0)
+                {
+                    var suggestionBuilder = new StringBuilder();
+                    for (int i = 0; i < suggestions.Count; i++)
+                    {
+                        if (i > 0)
+                        {
+                            suggestionBuilder.Append(i < suggestions.Count - 1 ? ", " : " or ");
+                        }
+
+                        suggestionBuilder.Append('"');
+                        suggestionBuilder.Append(suggestions[i]);
+                        suggestionBuilder.Append('"');
+                    }
+
+                    context.ReportDiagnostic(Diagnostic.Create(NoMatchingMethodOrTypeWithSuggestions, location, failedAttempt, suggestionBuilder));
+                }
+                else
+                {
+                    context.ReportDiagnostic(Diagnostic.Create(NoMatchingMethodOrType, location, failedAttempt));
+                }
+            }
         }
     }
 }