mapreduce| Adds map/reduce functionality to SimilarChecker

Before adding a new mixin this proves the concept works, adding tests as
examples of how this would work in the main linter.

The idea here is that, because `check_parallel()` uses a multiprocess
`map` function, that the natural follow on is to use a 'reduce`
paradigm. This should demonstrate that.

4 files changed, 267 insertions, 1 deletions

diff --git a/pylint/checkers/similar.py b/pylint/checkers/similar.py
index 82f79e8cc..3ac071bb3 100644
--- a/pylint/checkers/similar.py
+++ b/pylint/checkers/similar.py
@@ -160,6 +160,20 @@ class Similar:
             for lineset2 in self.linesets[idx + 1 :]:
                 yield from self._find_common(lineset, lineset2)
 
+    def get_map_data(self):
+        """Returns the data we can use for a map/reduce process
+
+        In this case we are returning this instance's Linesets, that is all file
+        information that will later be used for vectorisation.
+        """
+        return self.linesets
+
+    def combine_mapreduce_data(self, linesets_collection):
+        """Reduces and recombines data into a format that we can report on
+
+        The partner function of get_map_data()"""
+        self.linesets = [line for lineset in linesets_collection for line in lineset]
+
 
 def stripped_lines(lines, ignore_comments, ignore_docstrings, ignore_imports):
     """return lines with leading/trailing whitespace and any ignored code
@@ -352,7 +366,7 @@ class SimilarChecker(BaseChecker, Similar):
     def set_option(self, optname, value, action=None, optdict=None):
         """method called to set an option (registered in the options list)
 
-        overridden to report options setting to Similar
+        Overridden to report options setting to Similar
         """
         BaseChecker.set_option(self, optname, value, action, optdict)
         if optname == "min-similarity-lines":
@@ -402,6 +416,20 @@ class SimilarChecker(BaseChecker, Similar):
         stats["nb_duplicated_lines"] = duplicated
         stats["percent_duplicated_lines"] = total and duplicated * 100.0 / total
 
+    def get_map_data(self):
+        """ Passthru override """
+        return Similar.get_map_data(self)
+
+    @classmethod
+    def reduce_map_data(cls, linter, data):
+        """Reduces and recombines data into a format that we can report on
+
+        The partner function of get_map_data()"""
+        recombined = SimilarChecker(linter)
+        recombined.open()
+        Similar.combine_mapreduce_data(recombined, linesets_collection=data)
+        recombined.close()
+
 
 def register(linter):
     """required method to auto register this checker """
diff --git a/tests/checkers/unittest_similar.py b/tests/checkers/unittest_similar.py
index ed4af2f5c..ebc5c3ba1 100644
--- a/tests/checkers/unittest_similar.py
+++ b/tests/checkers/unittest_similar.py
@@ -21,6 +21,8 @@ from pathlib import Path
 import pytest
 
 from pylint.checkers import similar
+from pylint.lint import PyLinter
+from pylint.testutils import GenericTestReporter as Reporter
 
 INPUT = Path(__file__).parent / ".." / "input"
 SIMILAR1 = str(INPUT / "similar1")
@@ -234,3 +236,140 @@ def test_no_args():
             assert ex.code == 1
         else:
             pytest.fail("not system exit")
+
+
+def test_get_map_data():
+    """Tests that a SimilarChecker respects the MapReduceMixin interface"""
+    linter = PyLinter(reporter=Reporter())
+
+    # Add a parallel checker to ensure it can map and reduce
+    linter.register_checker(similar.SimilarChecker(linter))
+
+    source_streams = (
+        str(INPUT / "similar_lines_a.py"),
+        str(INPUT / "similar_lines_b.py"),
+    )
+    expected_linelists = (
+        (
+            "",
+            "",
+            "",
+            "",
+            "",
+            "",
+            "def adipiscing(elit):",
+            'etiam = "id"',
+            'dictum = "purus,"',
+            'vitae = "pretium"',
+            'neque = "Vivamus"',
+            'nec = "ornare"',
+            'tortor = "sit"',
+            "return etiam, dictum, vitae, neque, nec, tortor",
+            "",
+            "",
+            "class Amet:",
+            "def similar_function_3_lines(self, tellus):",
+            "agittis = 10",
+            "tellus *= 300",
+            "return agittis, tellus",
+            "",
+            "def lorem(self, ipsum):",
+            'dolor = "sit"',
+            'amet = "consectetur"',
+            "return (lorem, dolor, amet)",
+            "",
+            "def similar_function_5_lines(self, similar):",
+            "some_var = 10",
+            "someother_var *= 300",
+            'fusce = "sit"',
+            'amet = "tortor"',
+            "return some_var, someother_var, fusce, amet",
+            "",
+            'def __init__(self, moleskie, lectus="Mauris", ac="pellentesque"):',
+            'metus = "ut"',
+            'lobortis = "urna."',
+            'Integer = "nisl"',
+            '(mauris,) = "interdum"',
+            'non = "odio"',
+            'semper = "aliquam"',
+            'malesuada = "nunc."',
+            'iaculis = "dolor"',
+            'facilisis = "ultrices"',
+            'vitae = "ut."',
+            "",
+            "return (",
+            "metus,",
+            "lobortis,",
+            "Integer,",
+            "mauris,",
+            "non,",
+            "semper,",
+            "malesuada,",
+            "iaculis,",
+            "facilisis,",
+            "vitae,",
+            ")",
+            "",
+            "def similar_function_3_lines(self, tellus):",
+            "agittis = 10",
+            "tellus *= 300",
+            "return agittis, tellus",
+        ),
+        (
+            "",
+            "",
+            "",
+            "",
+            "",
+            "",
+            "",
+            "class Nulla:",
+            'tortor = "ultrices quis porta in"',
+            'sagittis = "ut tellus"',
+            "",
+            "def pulvinar(self, blandit, metus):",
+            "egestas = [mauris for mauris in zip(blandit, metus)]",
+            "neque = (egestas, blandit)",
+            "",
+            "def similar_function_5_lines(self, similar):",
+            "some_var = 10",
+            "someother_var *= 300",
+            'fusce = "sit"',
+            'amet = "tortor"',
+            'iaculis = "dolor"',
+            "return some_var, someother_var, fusce, amet, iaculis, iaculis",
+            "",
+            "",
+            "def tortor(self):",
+            "ultrices = 2",
+            'quis = ultricies * "porta"',
+            "return ultricies, quis",
+            "",
+            "",
+            "class Commodo:",
+            "def similar_function_3_lines(self, tellus):",
+            "agittis = 10",
+            "tellus *= 300",
+            'laoreet = "commodo "',
+            "return agittis, tellus, laoreet",
+        ),
+    )
+
+    data = []
+
+    # Manually perform a 'map' type function
+    for source_fname in source_streams:
+        sim = similar.SimilarChecker(linter)
+        with open(source_fname) as stream:
+            sim.append_stream(source_fname, stream)
+        # The map bit, can you tell? ;)
+        data.extend(sim.get_map_data())
+
+    assert len(expected_linelists) == len(data)
+    for source_fname, expected_lines, lineset_obj in zip(
+        source_streams, expected_linelists, data
+    ):
+        assert source_fname == lineset_obj.name
+        # There doesn't seem to be a faster way of doing this, yet.
+        lines = (line for idx, line in lineset_obj.enumerate_stripped())
+        assert tuple(expected_lines) == tuple(lines)
diff --git a/tests/input/similar_lines_a.py b/tests/input/similar_lines_a.py
new file mode 100644
index 000000000..65a72a79d
--- /dev/null
+++ b/tests/input/similar_lines_a.py
@@ -0,0 +1,63 @@
+""" A file designed to have lines of similarity when compared to similar_lines_b
+
+We use lorm-ipsum to generate 'random' code. """
+# Copyright (c) 2020 Frank Harrison <frank@doublethefish.com>
+
+
+def adipiscing(elit):
+    etiam = "id"
+    dictum = "purus,"
+    vitae = "pretium"
+    neque = "Vivamus"
+    nec = "ornare"
+    tortor = "sit"
+    return etiam, dictum, vitae, neque, nec, tortor
+
+
+class Amet:
+    def similar_function_3_lines(self, tellus):  # line same #1
+        agittis = 10  # line same #2
+        tellus *= 300  # line same #3
+        return agittis, tellus  # line diff
+
+    def lorem(self, ipsum):
+        dolor = "sit"
+        amet = "consectetur"
+        return (lorem, dolor, amet)
+
+    def similar_function_5_lines(self, similar):  # line same #1
+        some_var = 10  # line same #2
+        someother_var *= 300  # line same #3
+        fusce = "sit"  # line same #4
+        amet = "tortor"  # line same #5
+        return some_var, someother_var, fusce, amet  # line diff
+
+    def __init__(self, moleskie, lectus="Mauris", ac="pellentesque"):
+        metus = "ut"
+        lobortis = "urna."
+        Integer = "nisl"
+        (mauris,) = "interdum"
+        non = "odio"
+        semper = "aliquam"
+        malesuada = "nunc."
+        iaculis = "dolor"
+        facilisis = "ultrices"
+        vitae = "ut."
+
+        return (
+            metus,
+            lobortis,
+            Integer,
+            mauris,
+            non,
+            semper,
+            malesuada,
+            iaculis,
+            facilisis,
+            vitae,
+        )
+
+    def similar_function_3_lines(self, tellus):  # line same #1
+        agittis = 10  # line same #2
+        tellus *= 300  # line same #3
+        return agittis, tellus  # line diff
diff --git a/tests/input/similar_lines_b.py b/tests/input/similar_lines_b.py
new file mode 100644
index 000000000..21634883d
--- /dev/null
+++ b/tests/input/similar_lines_b.py
@@ -0,0 +1,36 @@
+""" The sister file of similar_lines_a, another file designed to have lines of
+similarity when compared to its sister file
+
+As with the sister file, we use lorm-ipsum to generate 'random' code. """
+# Copyright (c) 2020 Frank Harrison <frank@doublethefish.com>
+
+
+class Nulla:
+    tortor = "ultrices quis porta in"
+    sagittis = "ut tellus"
+
+    def pulvinar(self, blandit, metus):
+        egestas = [mauris for mauris in zip(blandit, metus)]
+        neque = (egestas, blandit)
+
+    def similar_function_5_lines(self, similar):  # line same #1
+        some_var = 10  # line same #2
+        someother_var *= 300  # line same #3
+        fusce = "sit"  # line same #4
+        amet = "tortor"  # line same #5
+        iaculis = "dolor"  # line diff
+        return some_var, someother_var, fusce, amet, iaculis, iaculis  # line diff
+
+
+def tortor(self):
+    ultrices = 2
+    quis = ultricies * "porta"
+    return ultricies, quis
+
+
+class Commodo:
+    def similar_function_3_lines(self, tellus):  # line same #1
+        agittis = 10  # line same #2
+        tellus *= 300  # line same #3
+        laoreet = "commodo "  # line diff
+        return agittis, tellus, laoreet  # line diff