add if_match to allow skipping suggestions

languagetool-core/src/main/java/org/languagetool/rules/patterns/Match.java

@@ -51,6 +51,8 @@ public enum IncludeRange {
   private final IncludeRange includeSkipped;
   // Pattern used to define parts of the matched token:
   private final Pattern pRegexMatch;
+  // if true the suggestion will only be applied if match is successful
+  private boolean ifMatch;
   // True if this match element is used for formatting POS token:
   private final boolean setPos;
 
@@ -228,4 +230,12 @@ public IncludeRange getIncludeSkipped() {
     return includeSkipped;
   }
 
+  public boolean isIfMatch() {
+    return ifMatch;
+  }
+
+  public void setIfMatch(boolean ifMatch) {
+    this.ifMatch = ifMatch;
+  }
+
 }

languagetool-core/src/main/java/org/languagetool/rules/patterns/MatchState.java

@@ -24,6 +24,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.TreeSet;
+import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 import org.apache.commons.lang3.StringUtils;
@@ -45,7 +46,10 @@
  * @since 2.3
  */
 public class MatchState {
-
+  // use private Unicode char for suggestions to filter out
+  // we can't use empty string as existing tests expect it and it's hard to signal skipping in other ways
+  static final String DONT_APPLY = "\uE120";
+
   private final Match match;
   private final Synthesizer synthesizer;
 
@@ -224,7 +228,11 @@ public final String[] toFinalString(Language lang) throws IOException {
         if (lang != null && lang.getShortCode().equals("ar")) {
            formattedString[0] = StringTools.removeTashkeel(formattedString[0]);
         }
-        formattedString[0] = pRegexMatch.matcher(formattedString[0]).replaceAll(regexReplace);
+        Matcher matcher = pRegexMatch.matcher(formattedString[0]);
+        if( match.isIfMatch() && ! matcher.find() ) {
+          return new String[] { DONT_APPLY };
+        }
+        formattedString[0] = matcher.replaceAll(regexReplace);
       }
 
       String posTag = match.getPosTag();

languagetool-core/src/main/java/org/languagetool/rules/patterns/PatternRuleMatcher.java

@@ -30,6 +30,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.stream.Stream;
 
 //import org.slf4j.Logger;
 //import org.slf4j.LoggerFactory;
@@ -394,7 +395,10 @@ static String formatMultipleSynthesis(String[] matches,
     }
     int lastLeftSugEnd = leftSide.indexOf(RuleMatch.SUGGESTION_END_TAG);
     int lastLeftSugStart = leftSide.lastIndexOf(RuleMatch.SUGGESTION_START_TAG);
-    StringBuilder sb = new StringBuilder();
+
+    matches = filterOutEmpty(matches);
+
+    StringBuilder sb = new StringBuilder(leftSide.length() + rightSide.length() + 40 * matches.length);
     sb.append(errorMessage);
     for (int z = 0; z < matches.length; z++) {
       sb.append(suggestionLeft);
@@ -443,6 +447,12 @@ private String[] concatMatches(int start, int index,
     return finalMatch;
   }
 
+  private static String[] filterOutEmpty(String[] finalMatch) {
+    return Stream.of(finalMatch)
+        .filter(m -> ! MatchState.DONT_APPLY.equals(m))
+        .toArray(String[]::new);
+  }
+
   private int phraseLen(int i) {
     PatternRule rule = (PatternRule) this.rule;
     List<Integer> elementNo = rule.getElementNo();

languagetool-core/src/main/java/org/languagetool/rules/patterns/XMLRuleHandler.java

@@ -390,6 +390,7 @@ protected void setMatchElement(Attributes attrs, boolean isSuppressMisspelled) t
         caseConversion, YES.equals(attrs.getValue("setpos")),
         isSuppressMisspelled,
         includeRange);
+    mWorker.setIfMatch(YES.equals(attrs.getValue("if_match")));
     mWorker.setInMessageOnly(!inSuggestion);
     if (inMessage) {
       suggestionMatches.add(mWorker);

languagetool-core/src/main/resources/org/languagetool/rules/pattern.xsd

@@ -101,6 +101,7 @@
 	<xs:complexType mixed="true">
 		<xs:attribute name="no" type="xs:nonNegativeInteger" use="required" />
 		<xs:attribute name="regexp_match" type="xs:string" use="optional" />
+		<xs:attribute name="if_match" type="xs:string" use="optional" />
 		<xs:attribute name="regexp_replace" type="xs:string" use="optional" />
 		<xs:attribute name="postag_regexp" type="binaryYesNo" use="optional" default="no" />
 		<xs:attribute name="postag" type="xs:string" use="optional" />

languagetool-core/src/test/java/org/languagetool/rules/patterns/DemoPatternRuleTest.java

@@ -139,6 +139,12 @@ public void testFormatMultipleSynthesis() throws Exception {
     assertEquals("This is how you should write: <suggestion>test</suggestion>, <suggestion> </suggestion>.",
             PatternRuleMatcher.formatMultipleSynthesis(suggestions2,
                     "This is how you should write: <suggestion>", "</suggestion>."));
+
+    String[] suggestions3 = { "test", MatchState.DONT_APPLY };
+
+    assertEquals("This is how you should write: <suggestion>test</suggestion>.",
+            PatternRuleMatcher.formatMultipleSynthesis(suggestions3,
+                    "This is how you should write: <suggestion>", "</suggestion>."));
   }
 
   private PatternRule makePatternRule(String s) {

languagetool-core/src/test/java/org/languagetool/rules/patterns/PatternRuleTest.java

@@ -758,6 +758,8 @@ private void assertSuggestions(String sentence, List<String> expectedCorrections
         }
       }
       List<String> realSuggestions = matches.get(0).getSuggestedReplacements();
+      realSuggestions = new ArrayList<>(realSuggestions);
+      realSuggestions.removeIf(s -> MatchState.DONT_APPLY.equals(s));
       if (realSuggestions.isEmpty()) {
         boolean expectedEmptyCorrection = expectedCorrections.size() == 1 && expectedCorrections.get(0).length() == 0;
         if (!expectedEmptyCorrection) {

languagetool-core/src/test/resources/org/languagetool/rules/xx/grammar.xml

@@ -377,6 +377,16 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
                 <example correction="geheißen">Sie hat früher Müller <marker>gehießen</marker>.</example>
             </rule>
         </rulegroup>
+        <!-- we're ignoring two matches, and using only one -->
+        <rule id="TEST_IF_MATCH" name="If match test">
+            <pattern>
+              <token>token</token>
+            </pattern> 
+            <message>You could use: <match no="1" if_match="yes" regexp_match="t(.*)x" regexp_replace="b$1"/></message>
+            <suggestion><match no="1" if_match="yes" regexp_match="t(.*)n" regexp_replace="moke"/></suggestion>
+            <suggestion><match no="1" if_match="yes" regexp_match="t(.*)x" regexp_replace="l$1"/></suggestion>
+            <example correction="moke">It's a <marker>token</marker>.</example>
+        </rule>
     </category>
 
     <category id="OTHER" name="otherCategory" type="addition">