plc4net/tools/code-gen/MspecReader.cs

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// to you under the Apache License, Version 2.0 (the
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//
//      https://www.apache.org/licenses/LICENSE-2.0
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// KIND, either express or implied.  See the License for the
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using System.IO;
using System.Linq;
using Antlr4.Runtime;
using org.apache.plc4net.tools.codegen.grammar;

namespace org.apache.plc4net.tools.codegen
{
    /// <summary>
    /// Parses an mspec protocol description file into an ANTLR parse tree.
    /// This is the first stage of the pure-.NET mspec toolchain: the grammar
    /// layer that turns text into a parse tree. The type model layer (the
    /// next stage) walks the tree with a listener.
    /// </summary>
    public static class MspecReader
    {
        /// <summary>
        /// Parses the content of an mspec file and returns the parse tree root.
        /// </summary>
        /// <summary>
        /// The empty-string literal <c>''</c> - which the shared expression
        /// grammar's <c>TICK innerExpression TICK</c> rule cannot match (the
        /// inner is not optional) - rewritten to a sentinel the model builder
        /// maps back to <c>""</c>. It appears only in knx-master-data.mspec's
        /// <c>KnxDatapointType</c> table, for the IEC-type rows with no DPST id.
        /// </summary>
        public const string EmptyStringSentinel = "__plc4net_empty_string__";

        public static MSpecParser.FileContext Read(string mspecContent, bool strict = true)
        {
            mspecContent = mspecContent.Replace("''", "'" + EmptyStringSentinel + "'");
            var inputStream = new AntlrInputStream(mspecContent);
            var lexer = new MSpecLexer(inputStream);
            var lexerErrors = new LexerErrorListener();
            lexer.RemoveErrorListeners();
            lexer.AddErrorListener(lexerErrors);
            var tokenStream = new CommonTokenStream(lexer);
            var parser = new MSpecParser(tokenStream);

            // Collect errors rather than printing to stderr.
            var errorListener = new CollectingErrorListener();
            parser.RemoveErrorListeners();
            parser.AddErrorListener(errorListener);

            var tree = parser.file();

            var errors = lexerErrors.Errors.Concat(errorListener.Errors).ToArray();
            if (errors.Length != 0 && strict)
            {
                throw new MspecParseException(
                    $"Failed to parse mspec: {string.Join("; ", errors)}");
            }

            // Non-strict: ANTLR's error recovery has already skipped the bad
            // tokens and produced a best-effort tree. The Java MessageFormatParser
            // behaves the same on knx-master-data.mspec (it logs the same
            // "mismatched input" lines to stderr and carries on).
            LastErrors = errors;
            return tree;
        }

        /// <summary>Syntax errors from the most recent non-strict
        /// <see cref="Read(string, bool)"/>, for a caller that wants to report them.</summary>
        public static System.Collections.Generic.IReadOnlyList<string> LastErrors { get; private set; }
            = System.Array.Empty<string>();

        /// <summary>
        /// Parses an mspec file at the given path.
        /// </summary>
        public static MSpecParser.FileContext ReadFile(string filePath, bool strict = true)
        {
            return Read(File.ReadAllText(filePath), strict);
        }
    }

    /// <summary>
    /// Collects syntax errors rather than printing them.
    /// </summary>
    internal class CollectingErrorListener : BaseErrorListener
    {
        private readonly System.Collections.Generic.List<string> _errors
            = new System.Collections.Generic.List<string>();

        public System.Collections.Generic.IReadOnlyList<string> Errors => _errors;

        public bool HasErrors => _errors.Count > 0;

        public override void SyntaxError(TextWriter output, IRecognizer recognizer,
            IToken offendingSymbol, int line, int charPositionInLine,
            string msg, RecognitionException e)
        {
            _errors.Add($"line {line}:{charPositionInLine} {msg}");
        }
    }

    internal sealed class LexerErrorListener : IAntlrErrorListener<int>
    {
        public System.Collections.Generic.List<string> Errors { get; } = new System.Collections.Generic.List<string>();

        public void SyntaxError(TextWriter output, IRecognizer recognizer, int offendingSymbol,
            int line, int charPositionInLine, string msg, RecognitionException e)
        {
            Errors.Add($"line {line}:{charPositionInLine} {msg}");
        }
    }

}