[GitHub] [lucene-solr] donnerpeter commented on a change in pull request #2423: LUCENE-9806: Hunspell: speed up affix condition checking

[GitBox <gi...@apache.org>]

donnerpeter commented on a change in pull request #2423:
URL: https://github.com/apache/lucene-solr/pull/2423#discussion_r581269799



##########
File path: lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/AffixCondition.java
##########
@@ -0,0 +1,214 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.analysis.hunspell;
+
+import static org.apache.lucene.analysis.hunspell.AffixKind.PREFIX;
+import static org.apache.lucene.analysis.hunspell.AffixKind.SUFFIX;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.PatternSyntaxException;
+import java.util.stream.Collectors;
+import org.apache.lucene.util.automaton.CharacterRunAutomaton;
+import org.apache.lucene.util.automaton.RegExp;
+
+/**
+ * Checks the "condition" part of affix definition, as in
+ *
+ * <pre>PFX flag stripping prefix [condition [morphological_fields...]]</pre>
+ */
+interface AffixCondition {
+  String ALWAYS_TRUE_KEY = ".*";
+  AffixCondition ALWAYS_TRUE = (word, offset, length) -> true;
+  AffixCondition ALWAYS_FALSE = (word, offset, length) -> false;
+
+  default boolean acceptsStem(String stem) {
+    return acceptsStem(stem.toCharArray(), 0, stem.length());
+  }
+
+  /**
+   * @return whether the given word matches this condition as a stem with both "strip" and "affix"
+   *     removed
+   */
+  boolean acceptsStem(char[] word, int offset, int length);
+
+  /**
+   * @return a key used to deduplicate same condition+strip+kind triples. For trivial conditions
+   *     that need no check, {@link #ALWAYS_TRUE_KEY} is returned.
+   */
+  static String uniqueKey(AffixKind kind, String strip, String condition) {
+    if (".".equals(condition)
+        || kind == PREFIX && strip.startsWith(condition)
+        || kind == SUFFIX && strip.endsWith(condition) && !isRegexp(condition)) {
+      return ALWAYS_TRUE_KEY;
+    }
+    return kind == SUFFIX ? ".*" + condition : condition + ".*";
+  }
+
+  /**
+   * Analyzes the given affix kind, strip and condition and returns an object able to efficiently
+   * check that condition.
+   */
+  static AffixCondition compile(AffixKind kind, String strip, String condition, String line) {
+    String stemCondition = removeStrip(strip, condition, line, kind);
+    if (stemCondition == null) {
+      return ALWAYS_FALSE;
+    }
+
+    if (stemCondition.isEmpty()) {
+      return ALWAYS_TRUE;
+    }
+
+    if (!isRegexp(stemCondition)) {
+      return substringCondition(kind, stemCondition);
+    }
+
+    try {
+      return regexpCondition(kind, escapeDash(stemCondition));
+    } catch (IllegalArgumentException e) {
+      throw new IllegalArgumentException("On line: " + line, e);
+    }
+  }
+
+  private static boolean isRegexp(String condition) {
+    return condition.contains("[") || condition.contains(".") || condition.contains("-");
+  }
+
+  /** Removes the "strip" from "condition", to check only the remaining stem part */
+  private static String removeStrip(String strip, String condition, String line, AffixKind kind) {
+    if (!isRegexp(condition)) {
+      if (kind == SUFFIX && condition.endsWith(strip)) {
+        return condition.substring(0, condition.length() - strip.length());
+      }
+      if (kind == PREFIX && condition.startsWith(strip)) {
+        return condition.substring(strip.length());
+      }
+    }
+
+    List<String> charPatterns = parse(condition);
+    try {
+      if (charPatterns.size() < strip.length()) {
+        String regexp = unitePatterns(charPatterns);
+        return strip.matches(kind == SUFFIX ? ".*" + regexp : regexp + ".*") ? "" : null;
+      }
+
+      int stripRangeStart = kind == PREFIX ? 0 : charPatterns.size() - strip.length();
+      int stripRangeEnd = kind == PREFIX ? strip.length() : charPatterns.size();
+      if (!strip.isEmpty()
+          && !strip.matches(unitePatterns(charPatterns.subList(stripRangeStart, stripRangeEnd)))) {
+        return null;
+      }
+
+      if (kind == PREFIX) {
+        return unitePatterns(charPatterns.subList(stripRangeEnd, charPatterns.size()));
+      }
+      return unitePatterns(charPatterns.subList(0, stripRangeStart));
+    } catch (PatternSyntaxException e) {
+      throw new IllegalArgumentException("On line " + line, e);
+    }
+  }
+
+  /** Produces a regexp from groups returned by {@link #parse} */
+  private static String unitePatterns(List<String> charPatterns) {
+    return charPatterns.stream()
+        .map(s -> s.length() == 1 && "()?$^{}*+|\\".indexOf(s.charAt(0)) >= 0 ? "\\" + s : s)
+        .collect(Collectors.joining());
+  }

Review comment:
       It's concatenation. Maybe `unite` isn't such a great name after all. Would `join` be better?




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