Find a code pattern in C# files

find-code.cs

// Copyright (C) 2019 Dmitry Yakimenko (detunized@gmail.com).
// Licensed under the terms of the MIT license. See LICENCE for details.

using System;
using System.IO;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace NunitToXunit
{
    using static SyntaxFactory;

    public static class Ast
    {
        private class Matcher
        {
            public bool Match(SyntaxNode code, SyntaxNode pattern)
            {
                // A placeholder matches anything
                if (IsPlaceholder(pattern))
                    return true;

                if (code.GetType() != pattern.GetType())
                    return false;

                switch (code)
                {
                case ArgumentSyntax c:
                    {
                        var p = (ArgumentSyntax)pattern;
                        return Match(c.Expression, p.Expression);
                    }
                case ArgumentListSyntax c:
                    {
                        var p = (ArgumentListSyntax)pattern;
                        return Match(c.OpenParenToken, p.OpenParenToken)
                            && Match(c.Arguments, p.Arguments)
                            && Match(c.CloseParenToken, p.CloseParenToken);
                    }
                case IdentifierNameSyntax c:
                    {
                        var p = (IdentifierNameSyntax)pattern;
                        return Match(c.Identifier, p.Identifier);
                    }
                case InvocationExpressionSyntax c:
                    {
                        var p = (InvocationExpressionSyntax)pattern;
                        return Match(c.Expression, p.Expression)
                            && Match(c.ArgumentList, p.ArgumentList);
                    }
                case LiteralExpressionSyntax c:
                    {
                        var p = (LiteralExpressionSyntax)pattern;
                        return Match(c.Token, p.Token);
                    }
                case MemberAccessExpressionSyntax c:
                    {
                        var p = (MemberAccessExpressionSyntax)pattern;
                        return Match(c.Expression, p.Expression)
                            && Match(c.Name, p.Name);
                    }
                case GenericNameSyntax c:
                    {
                        var p = (GenericNameSyntax)pattern;
                        return Match(c.Identifier, p.Identifier)
                            && Match(c.TypeArgumentList, p.TypeArgumentList);
                    }
                case TypeArgumentListSyntax c:
                    {
                        var p = (TypeArgumentListSyntax)pattern;
                        return Match(c.LessThanToken, p.LessThanToken)
                            && Match(c.Arguments, p.Arguments)
                            && Match(c.GreaterThanToken, p.GreaterThanToken);
                    }
                default:
                    return false;
                }
            }

            //
            // Private
            //

            private bool Match<T>(SeparatedSyntaxList<T> code, SeparatedSyntaxList<T> pattern) where T : SyntaxNode
            {
                if (code.Count != pattern.Count)
                    return false;

                for (var i = 0; i < code.Count; i++)
                    if (!Match(code[i], pattern[i]))
                        return false;

                return true;
            }

            private bool Match(SyntaxToken code, SyntaxToken pattern)
            {
                if (IsPlaceholder(pattern.Text))
                    return true;

                if (code.ValueText == pattern.ValueText)
                    return true;

                return false;
            }

            private bool IsPlaceholder(SyntaxNode pattern)
            {
                return pattern is IdentifierNameSyntax i
                    && IsPlaceholder(i.Identifier.Text);
            }

            private bool IsPlaceholder(string name)
            {
                if (name == "_")
                    return true;

                return false;
            }
        }

        public static ExpressionSyntax Parse(string pattern)
        {
            return ParseExpression(pattern);
        }

        public static bool Match(SyntaxNode code, SyntaxNode pattern)
        {
            return new Matcher().Match(code, pattern);
        }
    }

    static class Program
    {
        static void FindMatches(string filename, string pattern)
        {
            var sourceAst = CSharpSyntaxTree.ParseText(File.ReadAllText(filename));
            var patternAst = Ast.Parse(pattern);
            var nodes = sourceAst.GetRoot().DescendantNodes().OfType<ExpressionSyntax>();

            foreach (var e in nodes)
            {
                if (Ast.Match(e, patternAst))
                {
                    var line = e.GetLocation().GetLineSpan().StartLinePosition.Line;
                    var code = e.NormalizeWhitespace();
                    Console.WriteLine($"  {line}: {code}");
                }
            }
        }

        static void Main(string[] args)
        {
            if (args.Length < 2)
            {
                Console.WriteLine("USAGE: find-code pattern files...");
                return;
            }

            var pattern = args[0];
            Console.WriteLine($"Looking for '{pattern}'");

            foreach (var f in args.Skip(1))
            {
                Console.WriteLine(f);
                FindMatches(f, pattern);
            }
        }
    }
}