IDE0018 wanting to inline variable breaks compilation

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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Hence the following compilable code:

private static int Main(string[] args)
{
    Dictionary<int, int> dict = new Dictionary<int, int> { /* ... */ };
<span class=hljs-keyword>int</span> price; <span class=hljs-comment>// IDE0018</span>
<span class=hljs-keyword>bool</span> found = args[<span class=hljs-number>0</span>] <span class=hljs-keyword>switch</span>
{
    <span class=hljs-string>&quot;First&quot;</span> =&gt; dict.TryGetValue(<span class=hljs-number>1</span>, <span class=hljs-keyword>out</span> price),
    <span class=hljs-string>&quot;Second&quot;</span> =&gt; dict.TryGetValue(<span class=hljs-number>2</span>, <span class=hljs-keyword>out</span> price),
    _ =&gt; dict.TryGetValue(<span class=hljs-number>3</span>, <span class=hljs-keyword>out</span> price)
};

<span class=hljs-keyword>return</span> found ? <span class=hljs-number>-1</span> : price;

}

This will suggest IDE: 0018: Variable declaration can be inlined as marked by the comment above, suggesting to inline price to the first out variable:

private static int Main(string[] args)
{
    Dictionary<int, int> dict = new Dictionary<int, int> { /* ... */ };
<span class=hljs-keyword>bool</span> found = args[<span class=hljs-number>0</span>] <span class=hljs-keyword>switch</span>
{
    <span class=hljs-string>&quot;First&quot;</span> =&gt; dict.TryGetValue(<span class=hljs-number>1</span>, <span class=hljs-keyword>out</span> <span class=hljs-keyword>int</span> price), <span class=hljs-comment>// IDE0059</span>
    <span class=hljs-string>&quot;Second&quot;</span> =&gt; dict.TryGetValue(<span class=hljs-number>2</span>, <span class=hljs-keyword>out</span> price), <span class=hljs-comment>// CS0103</span>
    _ =&gt; dict.TryGetValue(<span class=hljs-number>3</span>, <span class=hljs-keyword>out</span> price) <span class=hljs-comment>// CS0103</span>
};

<span class=hljs-keyword>return</span> found ? <span class=hljs-number>-1</span> : price; <span class=hljs-comment>// CS0103</span>

}

This code does not compile due to multiple issues (all marked above):

• 1x warning IDE0059: Unnecessary assignment of a value to 'price’
• 3x error CS0103: The name ‘price’ does not exist in the current context

I don’t expect suggestions to break code when applied, so I’m reporting this as a bug.

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Original Comments

Visual Studio Feedback System on 12/29/2019, 10:15 PM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

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Original Solutions

(no solutions)

[zaytsev-victor]

First case:

        private static int Main(string[] args)
        {
            Dictionary<int, int> dict = new Dictionary<int, int> { /* ... */ };
            int price; // IDE0018 
            bool found = args[0] switch 
            { 
                "First" => dict.TryGetValue(1, out price), 
                "Second" => dict.TryGetValue(2, out price), 
                _ => dict.TryGetValue(3, out price) 
            }; 
            
            return found ? -1 : price;
        }

Second case:

        private static int Main(string[] args)
        {
            Dictionary<int, int> dict = new Dictionary<int, int> { /* ... */ };
            bool found = args[0] switch
            {
                "First" => dict.TryGetValue(1, out int price), // IDE0059 
                "Second" => dict.TryGetValue(2, out price), // CS0103 
                _ => dict.TryGetValue(3, out price) // CS0103 
            }; 
            
            return found ? -1 : price; // CS0103
        }

[RayKoopa]

Thanks for adding that. I didn't see the import here messed with my samples!

[zspitz]

Same thing here.