Convert LINQ to Foreach

Turns a LINQ query of Where and Select ending in ToList, Sum, Count or Any into a foreach loop that builds the same result. The reverse of Convert Foreach to LINQ.

var names = users.Where(user => user.IsActive).Select(user => user.Name).ToList();

becomes

var names = new List<string>();
foreach (var user in users)
{
    if (user.IsActive)
    {
        names.Add(user.Name);
    }
}

Target

The query, by a caret anywhere in the statement.

Precondition

• The query is the whole initializer of a local declaration, or the whole expression of a return, in a block.
• It is a chain of System.Linq.Enumerable calls on a source: any number of Where and Select, then one of ToList(), Sum(), Sum(selector), Count(), Count(predicate), Any() or Any(predicate).
• Every argument is a lambda with one parameter and an expression body, and is not async.
• A Sum is not of nullable values.
• The names the loop declares (the loop variable and a local for each Select followed by another lambda) are not already declared in scope.

Transformation

• The loop is foreach (var x in source), named after the first lambda's parameter, or after the singular of the source's name, or item.
• Each Where becomes an if around the rest of the body. A Select followed by another lambda becomes a local named after that lambda's parameter; a Select straight before ToList or Sum() becomes the value added. Later lambdas' parameters are renamed to the loop's current variable.
• The result accumulates in the declared local, keeping its written type. A var total, count or flag is declared with the result's type, since its starting value 0 or false would not say it.
• ToList starts from new List<T>() and calls Add, adding using System.Collections.Generic; when the file does not have it.
• Sum starts at 0 and adds with +=.
• Count starts at 0 and increments.
• Any starts at false and sets it to true and breaks on the first match.
• A returned query accumulates in a new local, arguments.name or result, total or count, returned after the loop; a returned Any returns true from the loop and false after it.

Preserved

• Behaviour: each element runs through the conditions and projections in the query's order, and Any stops at the first match.
• Comments above the statement stay above the accumulator, and a comment ending its line stays on the declaration.

Limitations

• Other operators (OrderBy, First, ToArray, query syntax and so on), method groups, and lambdas with a block body are refused.
• A Select whose values are only counted by Count() or Any() is refused.
• += does not check for overflow as Sum does, and adds float values as float where Sum adds them as double.
• The refactoring changes one statement, so there are no references in other files to update.

Error codes