dotnet/roslyn

Invalid IDE0059 When using constant inside static local function

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#44,948 opened on Jun 8, 2020

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Area-IDEBugFeature - IDE0059help wanted

Description

Version Used: Visual Studio 16.6.1

Steps to Reproduce:

using System;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var local = FormatDate(DateTime.Now);
            var utc = FormatUtcDate(DateTime.Now);
            Console.WriteLine("{0} -> {1}", local, utc);
            Console.ReadKey();

            const string DatePickerFormat = "MM/dd/yyyy hh:mm";
            static string FormatDate(DateTime? date) => date?.ToString(DatePickerFormat);
            static string FormatUtcDate(DateTime? date) => date?.ToUniversalTime().ToString(DatePickerFormat);
        }
    }
}

Expected Behavior: No IDE0059 notice will be shown for DatePickerFormat because it is used by the static local functions FormatDate and FormatUtcDate.

Actual Behavior: An IDE0059 notice is shown for DatePickerFormat .

Contributor guide

Tech stack
csharp
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
understanding of C# static local functionsfamiliarity with Roslyn analyzer infrastructure
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Start by locating the analyzer for IDE0059 (unused value assignment) in the Roslyn repository. Look in the 'src/Analyzers' or 'src/Features' directory for files related to 'UnusedValueAssignment' or 'IDE0059'. The bug is that a constant defined in the enclosing method is considered unused when referenced by a static local function. Investigate how the analyzer tracks usage across nested functions, particularly static local functions. Check if there is existing logic to handle closures but not static local functions. The fix may involve adding a test case and modifying the analysis to include static local function references.