IDE0120Unnecessary code rules (expression-level preferences)

Simplify LINQ expression

Description

This rule flags overly complex LINQ expressions, specifically expressions that call System.Linq.Enumerable.Where`1(System.Collections.Generic.IEnumerable{0},System.Func{`0,System.Int32,System.Boolean}) followed by one of the following methods:

System.Linq.Enumerable.Any`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.Count`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.First`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.FirstOrDefault`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.Last`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.LastOrDefault`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.Single`1(System.Collections.Generic.IEnumerable{`0})
System.Linq.Enumerable.SingleOrDefault`1(System.Collections.Generic.IEnumerable{`0})

Such expressions can be simplified by removing the call to System.Linq.Enumerable.Where`1(System.Collections.Generic.IEnumerable{0},System.Func{0,System.Int32,System.Boolean}) and instead calling an overload of Any(), Count(), First(), FirstOrDefault(), Last(), LastOrDefault(), Single, or SingleOrDefault()` that accepts a predicate function to filter the elements.

Example

// Code with violations.
IEnumerable<string> words = new List<string> { "hello", "world", "!" };
var result = words.Where(x => x.Equals("hello")).Any();

// Fixed code.
IEnumerable<string> words = new List<string> { "hello", "world", "!" };
var result = words.Any(x => x.Equals("hello"));

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