Fix remove cast in ternary (#79186)

Fixes: #79180

You can continue writing code this way when this fix arrives in VS,
Sergio 😎

Author: CyrusNajmabadi

src/Analyzers/CSharp/Tests/RemoveUnnecessaryCast/RemoveUnnecessaryCastTests.cs

@@ -14183,4 +14183,104 @@ public void ConvertFieldValueForStorage(object value)
             ReferenceAssemblies = ReferenceAssemblies.Net.Net80,
         }.RunAsync();
     }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79180")]
+    public async Task ImplicitNumericConversionCastInTernary1()
+    {
+        await VerifyCS.VerifyAnalyzerAsync("""
+            class C
+            {
+                private const int ConstInt = 1;
+
+                uint M(bool condition)
+                {
+                    return condition ? (uint)ConstInt : 0;
+                }
+            }
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79180")]
+    public async Task ImplicitNumericConversionCastInTernary2()
+    {
+        await VerifyCS.VerifyCodeFixAsync("""
+            class C
+            {
+                private const int ConstInt = 1;
+
+                uint M(bool condition)
+                {
+                    return condition ? [|(uint)|]ConstInt : 0u;
+                }
+            }
+            """, """
+            class C
+            {
+                private const int ConstInt = 1;
+            
+                uint M(bool condition)
+                {
+                    return condition ? ConstInt : 0u;
+                }
+            }
+            """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79180")]
+    public async Task ImplicitNumericConversionCastInTernary3()
+    {
+        await VerifyCS.VerifyCodeFixAsync("""
+                class C
+                {
+                    private const int ConstInt = 1;
+
+                    uint M(bool condition)
+                    {
+                        return condition ? [|(uint)|]ConstInt : [|(uint)|]0;
+                    }
+                }
+                """, """
+                class C
+                {
+                    private const int ConstInt = 1;
+            
+                    uint M(bool condition)
+                    {
+                        return condition ? ConstInt : (uint)0;
+                    }
+                }
+                """);
+    }
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79180")]
+    public async Task ImplicitNumericConversionCastInTernary4()
+    {
+        await new VerifyCS.Test
+        {
+            TestCode = """
+                class C
+                {
+                    private const int ConstInt = 1;
+
+                    uint M(bool condition)
+                    {
+                        return condition ? [|(uint)|]ConstInt : [|(uint)|]0;
+                    }
+                }
+                """,
+            FixedCode = """
+                class C
+                {
+                    private const int ConstInt = 1;
+            
+                    uint M(bool condition)
+                    {
+                        return condition ? (uint)ConstInt : 0;
+                    }
+                }
+                """,
+            CodeFixTestBehaviors = CodeFixTestBehaviors.FixOne | CodeFixTestBehaviors.SkipFixAllCheck,
+            DiagnosticSelector = d => d[1],
+        }.RunAsync();
+    }
 }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Simplification/Simplifiers/CastSimplifier.cs

@@ -548,7 +548,7 @@ private static bool IsConversionCastSafeToRemove(
             }
         }
 
-        // We can safely remove convertion to object in interpolated strings regardless of nullability
+        // We can safely remove conversion to object in interpolated strings regardless of nullability
         if (castNode.IsParentKind(SyntaxKind.Interpolation) && originalConversionOperation.Type?.SpecialType is SpecialType.System_Object)
             return true;
 
@@ -922,13 +922,17 @@ bool IsConditionalCastSafeToRemoveDueToConversionToOtherBranch()
             if (!otherSideType.Equals(thisSideRewrittenType))
                 return false;
 
-            // Now check that with the (T) cast removed, that the outer `x ? y : z` is still immediately converted to a
-            // 'T'. If so, we can remove this inner (T) cast.
+            // Now check that with the (T) cast removed, that the outer `x ? y : z` is still
+            // immediately implicitly converted to a 'T'. If so, we can remove this inner (T) cast.
 
             var rewrittenConditionalConvertedType = rewrittenSemanticModel.GetTypeInfo(rewrittenConditionalExpression, cancellationToken).ConvertedType;
             if (rewrittenConditionalConvertedType is null)
                 return false;
 
+            var outerConversion = rewrittenSemanticModel.GetConversion(rewrittenConditionalExpression, cancellationToken);
+            if (!outerConversion.IsImplicit)
+                return false;
+
             return rewrittenConditionalConvertedType.Equals(conversionOperation.Type);
         }
     }