Preserve MySQL double-dash and executable-comment semantics

src/main/java/net/sf/jsqlparser/parser/AbstractJSqlParser.java

@@ -109,6 +109,21 @@ public P withLegacyMySqlGroupBy(boolean enabled) {
         return withFeature(Feature.allowLegacyMySqlGroupBy, enabled);
     }
 
+    /**
+     * Resolves MySQL executable comments against this server version (for example 90702 for 9.7.2).
+     * Requires the MYSQL dialect. Rendered SQL reflects this version, without conditional wrappers.
+     * Without an explicit version, conditional executable comments raise a lexical error.
+     *
+     * @param version major * 10000 + minor * 100 + patch, from 0 through 999999
+     * @return this parser
+     */
+    public P withMySqlServerVersion(int version) {
+        if (version < 0 || version > 999999) {
+            throw new IllegalArgumentException("MySQL server version must be between 0 and 999999");
+        }
+        return withFeature(Feature.mySqlServerVersion, (long) version);
+    }
+
     public P withTimeOut(long timeOutMillSeconds) {
         return withFeature(Feature.timeOut, timeOutMillSeconds);
     }

src/main/java/net/sf/jsqlparser/parser/SimpleCharStream.java

@@ -60,7 +60,12 @@ public class SimpleCharStream {
     // the `#` in the token image. Wired (with the token manager's
     // configuration) before parsing, null keeps this inert.
     static final char HASH_SUBSTITUTION = '\u0001';
+    static final char MYSQL_MINUS_SUBSTITUTION = '\u0002';
+    static final char MYSQL_COMMENT_ERROR = '\u0003';
     FeatureConfiguration featureConfiguration;
+    private boolean mySqlExecutableComment;
+    String mySqlCommentError;
+    boolean mySqlMinusSubstitution;
 
     /**
      * Constructor.
@@ -173,8 +178,24 @@ protected void FillBuff() throws java.io.IOException {
      * Start.
      */
     public final char BeginToken() throws java.io.IOException {
+        mySqlMinusSubstitution = false;
+        if (mySqlCommentError != null) {
+            // Parser lookahead may catch lexical errors. Keep this failure sticky until ReInit
+            // rather than allowing a later token request to continue after the rejected marker.
+            return MYSQL_COMMENT_ERROR;
+        }
         tokenBegin = -1;
-        char c = readChar();
+        char c;
+        try {
+            c = readChar();
+        } catch (java.io.IOException e) {
+            if (!mySqlExecutableComment) {
+                throw e;
+            }
+            // JavaCC treats exceptions from BeginToken as EOF. Emit a real token whose lexical
+            // action reports the error, so an unclosed executable comment cannot succeed as SQL.
+            c = mySqlCommentError("Unterminated MySQL executable comment");
+        }
         tokenBegin = bufpos;
 
         absoluteTokenBegin = totalCharsRead;
@@ -183,10 +204,103 @@ public final char BeginToken() throws java.io.IOException {
                 && featureConfiguration.getAsBoolean(Feature.allowHashLineComments)) {
             buffer[bufpos] = HASH_SUBSTITUTION;
             c = HASH_SUBSTITUTION;
+        } else if ((c == '-' || c == '/' || c == '*') && featureConfiguration != null
+                && AbstractJSqlParser.Dialect.MYSQL.name()
+                        .equals(featureConfiguration.getValue(Feature.dialect))) {
+            c = mySqlCommentBoundary(c);
         }
         return c;
     }
 
+    /** Changes only token boundaries, never characters being scanned inside strings or names. */
+    private char mySqlCommentBoundary(char c) throws java.io.IOException {
+        if (c == '-') {
+            String following = peekCharacters(2);
+            if (following.length() == 2 && following.charAt(0) == '-'
+                    && !isMySqlCommentSpace(following.charAt(1))) {
+                mySqlMinusSubstitution = true;
+                buffer[bufpos] = MYSQL_MINUS_SUBSTITUTION;
+                return MYSQL_MINUS_SUBSTITUTION;
+            }
+        } else if (c == '*' && mySqlExecutableComment && peekCharacters(1).equals("/")) {
+            eraseCommentMarker(2);
+            mySqlExecutableComment = false;
+            return ' ';
+        } else if (c == '/') {
+            String following = peekCharacters(9);
+            if (following.startsWith("*!")) {
+                if (mySqlExecutableComment) {
+                    return mySqlCommentError("Nested MySQL executable comments are not supported");
+                }
+                int digits = mySqlCommentVersionLength(following);
+                if (digits > 0) {
+                    long target = featureConfiguration.getAsLong(Feature.mySqlServerVersion);
+                    if (target < 0 || target > 999999) {
+                        return mySqlCommentError("MySQL conditional executable comments require "
+                                + "withMySqlServerVersion(major * 10000 + minor * 100 + patch)");
+                    }
+                    int minimum = Integer.parseInt(following.substring(2, 2 + digits));
+                    if (minimum > target) {
+                        return c;
+                    }
+                }
+                eraseCommentMarker(3 + digits);
+                mySqlExecutableComment = true;
+                return ' ';
+            }
+        }
+        return c;
+    }
+
+    private static boolean isMySqlCommentSpace(char c) {
+        return c <= ' ' || c == '\u007f';
+    }
+
+    private static int mySqlCommentVersionLength(String following) {
+        if (following.length() < 7) {
+            return 0;
+        }
+        for (int i = 2; i < 7; i++) {
+            if (following.charAt(i) < '0' || following.charAt(i) > '9') {
+                return 0;
+            }
+        }
+        // MySQL recognizes a sixth digit only when followed by whitespace. Otherwise the
+        // five-digit prefix is the version and the remaining characters belong to the SQL body.
+        return following.length() >= 9 && following.charAt(7) >= '0'
+                && following.charAt(7) <= '9' && (following.charAt(8) == ' '
+                        || following.charAt(8) >= '\t' && following.charAt(8) <= '\r')
+                                ? 6
+                                : 5;
+    }
+
+    private String peekCharacters(int length) {
+        StringBuilder result = new StringBuilder(length);
+        try {
+            for (int i = 0; i < length; i++) {
+                result.append(readChar());
+            }
+        } catch (java.io.IOException ignored) {
+            // Only the successfully read characters need to be rewound, including at EOF.
+        }
+        backup(result.length());
+        return result.toString();
+    }
+
+    private void eraseCommentMarker(int length) throws java.io.IOException {
+        buffer[bufpos] = ' ';
+        for (int i = 1; i < length; i++) {
+            readChar();
+            buffer[bufpos] = ' ';
+        }
+        backup(length - 1);
+    }
+
+    private char mySqlCommentError(String message) {
+        mySqlCommentError = message;
+        return MYSQL_COMMENT_ERROR;
+    }
+
     protected final void UpdateLineColumn(char c) {
         column++;
 
@@ -330,6 +444,8 @@ public void ReInit(Provider dstream, int startline, int startcolumn, int buffers
         prevCharIsLF = prevCharIsCR = false;
         tokenBegin = inBuf = maxNextCharInd = 0;
         bufpos = -1;
+        mySqlExecutableComment = false;
+        mySqlCommentError = null;
     }
 
     /**
@@ -362,6 +478,8 @@ public String GetImage() {
         String image = doGetImage();
         if (!image.isEmpty() && image.charAt(0) == HASH_SUBSTITUTION) {
             image = "#" + image.substring(1);
+        } else if (!image.isEmpty() && image.charAt(0) == MYSQL_MINUS_SUBSTITUTION) {
+            image = "-" + image.substring(1);
         }
         return image;
     }

src/main/java/net/sf/jsqlparser/parser/feature/Feature.java

@@ -818,6 +818,14 @@ public enum Feature {
     /** Enables legacy GROUP BY ordering with the MYSQL dialect; disabled by default. */
     allowLegacyMySqlGroupBy(false),
 
+    /**
+     * Target MySQL version for executable comments, encoded as major * 10000 + minor * 100 + patch.
+     * A negative value leaves the version unspecified: conditional comments then fail instead of
+     * silently discarding SQL. Only used with the MYSQL dialect; unversioned comments need no
+     * value.
+     */
+    mySqlServerVersion(-1),
+
     // PERFORMANCE
 
     /**

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -2199,6 +2199,12 @@ TOKEN_MGR_DECLS : {
 
     private RowPatternTokenContext rowPatternContext;
 
+    private void reportMySqlCommentError() {
+        throw new TokenMgrException(input_stream.mySqlCommentError == null
+                ? "Unexpected control character" : input_stream.mySqlCommentError,
+                TokenMgrException.LEXICAL_ERROR);
+    }
+
     public void CommonTokenAction(Token t)
 	{
 		t.absoluteBegin = getCurrentTokenAbsolutePosition();
@@ -2889,6 +2895,18 @@ TOKEN : /* Operators */
 |   <OP_RSHIFT: ">>">
 |   <OP_JSON_PATH_DELETE: "#-">
 |   <OP_JSON_PATH_EXISTS: "@?">
+|   <OP_MINUS: "-">
+|   <MYSQL_MINUS: "\u0002"> {
+        if (!input_stream.mySqlMinusSubstitution) {
+            input_stream.mySqlCommentError = "Unexpected control character";
+            reportMySqlCommentError();
+        }
+        matchedToken.kind = OP_MINUS;
+        matchedToken.image = "-";
+    }
+|   <MYSQL_EXECUTABLE_COMMENT_ERROR: "\u0003"> {
+        reportMySqlCommentError();
+    }
 | 	<OP_DOUBLEAND: "&&">
 | 	<OP_CONTAINS: "&>">
 | 	<OP_CONTAINEDBY: "<&">

src/site/sphinx/usage.rst

@@ -863,6 +863,36 @@ One grammar covers every supported RDBMS, but a few pieces of syntax mean differ
 
 Features set explicitly *after* the preset win over it.
 
+MySQL comments
+~~~~~~~~~~~~~~
+
+With ``Dialect.MYSQL``, ``--`` starts a line comment only when followed by
+whitespace or a control character. Thus ``SELECT 1--2`` contains subtraction
+and a negative operand. SQL inside an unversioned executable comment is parsed
+normally: ``SELECT 1 /*! + 2 */`` becomes ``SELECT 1 + 2``. Optimizer hints
+(``/*+ ... */``) remain separate from executable comments.
+
+Conditional executable comments require an explicit target server version:
+
+.. code-block:: java
+
+    Statement stmt = CCJSqlParserUtil.parse(
+            "SELECT 1 /*!90702 + 2 */",
+            parser -> parser.withDialect(Dialect.MYSQL).withMySqlServerVersion(90702));
+
+The value is ``major * 10000 + minor * 100 + patch``; for example, ``90702``
+means 9.7.2 and ``260700`` means 26.7.0. Five-digit and six-digit comment version
+prefixes follow MySQL's whitespace rules. SQL for a newer server is ignored;
+SQL for the configured version or an older one participates in the AST.
+Both SQL renderers produce the resolved SQL for that target, without the
+conditional wrappers. Without a target, a conditional executable comment
+raises an error instead of silently discarding its SQL. This replaces the
+previous treatment of all executable comments as ordinary discarded comments.
+The same configuration applies to parsers constructed with a ``StreamProvider``
+or ``FeatureConfiguration``. Other dialects retain their comment behavior.
+Nested executable comments are rejected; nested-comment acceptance in other
+dialects is not a guarantee that the same SQL is valid on MySQL.
+
 ALTER column names
 ~~~~~~~~~~~~~~~~~~