Deprecate sphinx.util.stemmer in favour of snowballstemmer

PorterStemmer, BaseStemmer, PyStemmer, StandardStemmer, and get_stemmer are deprecated
sphinx.util.stemmer.porter is removed

AUTHORS

@@ -96,5 +96,3 @@ authors and projects:
 
 * sphinx.util.jsdump uses the basestring encoding from simplejson,
   written by Bob Ippolito, released under the MIT license
-* sphinx.util.stemmer was written by Vivake Gupta, placed in the
-  Public Domain

sphinx/search/en.py

@@ -2,8 +2,9 @@
 
 from typing import Dict
 
+import snowballstemmer
+
 from sphinx.search import SearchLanguage
-from sphinx.util.stemmer import get_stemmer
 
 english_stopwords = set("""
 a  and  are  as  at
@@ -211,7 +212,7 @@ class SearchEnglish(SearchLanguage):
     stopwords = english_stopwords
 
     def init(self, options: Dict) -> None:
-        self.stemmer = get_stemmer()
+        self.stemmer = snowballstemmer.stemmer('english')
 
     def stem(self, word: str) -> str:
-        return self.stemmer.stem(word.lower())
+        return self.stemmer.stemWord(word.lower())

sphinx/search/zh.py

@@ -4,8 +4,9 @@
 import re
 from typing import Dict, List
 
+import snowballstemmer
+
 from sphinx.search import SearchLanguage
-from sphinx.util.stemmer import get_stemmer
 
 try:
     import jieba
@@ -230,7 +231,7 @@ def init(self, options: Dict) -> None:
             if dict_path and os.path.isfile(dict_path):
                 jieba.load_userdict(dict_path)
 
-        self.stemmer = get_stemmer()
+        self.stemmer = snowballstemmer.stemmer('english')
 
     def split(self, input: str) -> List[str]:
         chinese: List[str] = []
@@ -252,8 +253,8 @@ def stem(self, word: str) -> str:
         should_not_be_stemmed = (
             word in self.latin_terms and
             len(word) >= 3 and
-            len(self.stemmer.stem(word.lower())) < 3
+            len(self.stemmer.stemWord(word.lower())) < 3
         )
         if should_not_be_stemmed:
             return word.lower()
-        return self.stemmer.stem(word.lower())
+        return self.stemmer.stemWord(word.lower())

sphinx/util/stemmer/__init__.py

@@ -1,37 +1,62 @@
 """Word stemming utilities for Sphinx."""
 
-from sphinx.util.stemmer.porter import PorterStemmer
+import warnings
 
-try:
-    from Stemmer import Stemmer as _PyStemmer
-    PYSTEMMER = True
-except ImportError:
-    PYSTEMMER = False
+import snowballstemmer
+
+from sphinx.deprecation import RemovedInSphinx70Warning
+
+
+class PorterStemmer:
+    def __init__(self):
+        warnings.warn(f"{self.__class__.__name__} is deprecated, use "
+                      "snowballstemmer.stemmer('english') instead.",
+                      RemovedInSphinx70Warning, stacklevel=2)
+        self.stemmer = snowballstemmer.stemmer('english')
+
+    def stem(self, p: str, i: int, j: int) -> str:
+        warnings.warn(f"{self.__class__.__name__}.stem() is deprecated, use "
+                      "snowballstemmer.stemmer('english').stemWord() instead.",
+                      RemovedInSphinx70Warning, stacklevel=2)
+        return self.stemmer.stemWord(p)
 
 
 class BaseStemmer:
+    def __init__(self):
+        warnings.warn(f"{self.__class__.__name__} is deprecated, use "
+                      "snowballstemmer.stemmer('english') instead.",
+                      RemovedInSphinx70Warning, stacklevel=3)
+
     def stem(self, word: str) -> str:
-        raise NotImplementedError()
+        raise NotImplementedError
 
 
 class PyStemmer(BaseStemmer):
-    def __init__(self) -> None:
-        self.stemmer = _PyStemmer('porter')
+    def __init__(self):  # NoQA
+        super().__init__()
+        self.stemmer = snowballstemmer.stemmer('english')
 
     def stem(self, word: str) -> str:
+        warnings.warn(f"{self.__class__.__name__}.stem() is deprecated, use "
+                      "snowballstemmer.stemmer('english').stemWord() instead.",
+                      RemovedInSphinx70Warning, stacklevel=2)
         return self.stemmer.stemWord(word)
 
 
-class StandardStemmer(PorterStemmer, BaseStemmer):
-    """All those porter stemmer implementations look hideous;
-    make at least the stem method nicer.
-    """
-    def stem(self, word: str) -> str:  # type: ignore
-        return super().stem(word, 0, len(word) - 1)
+class StandardStemmer(BaseStemmer):
+    def __init__(self):  # NoQA
+        super().__init__()
+        self.stemmer = snowballstemmer.stemmer('english')
+
+    def stem(self, word: str) -> str:
+        warnings.warn(f"{self.__class__.__name__}.stem() is deprecated, use "
+                      "snowballstemmer.stemmer('english').stemWord() instead.",
+                      RemovedInSphinx70Warning, stacklevel=2)
+        return self.stemmer.stemWord(word)
 
 
 def get_stemmer() -> BaseStemmer:
-    if PYSTEMMER:
-        return PyStemmer()
-    else:
-        return StandardStemmer()
+    warnings.warn("get_stemmer() is deprecated, use "
+                  "snowballstemmer.stemmer('english') instead.",
+                  RemovedInSphinx70Warning, stacklevel=2)
+    return PyStemmer()