Implement checkstyle rules for App Inventor (#2149)

* Implement checkstyle rules for App Inventor

This commit implements checkstyle for App Inventor's Java code. The
App Inventor style rules are based on the Google style rules, with an
exception added for methods in the components/runtime package that are
annotated with `@Simple*` or `@Design*` annotations. The App Inventor
specific rules are placed at the end of the appinventor_checks.xml
file.

In addition, there is a script called checkstyle_git.py that is
written in Python 3 and will check the git diff against the rules by
running checkstyle on the changed files and crossreferencing the line
numbers with the checkstyle output. This can be used as a git
pre-commit hook to check that changes conform to the style guide. The
script returns -1 on error, which will abort the commit until the
changes confirm. This behavior can be bypassed by exporting the
BYPASS_CHECKSTYLE environment variable.

These two changes are made available as ant targets:

- `ant checkstyle`: Run the checkstyle_git.py script to check the
  git diff for problems.
- `ant checkstyle-all`: Run checkstyle on the whole repo (slow).

Change-Id: I26c6049bd49d1ce3f9b8dbd48f8f115a89fb5b52

* Revamp checkstyle-git script logic

Change-Id: Ie417057b2d009ba70279e70df102851b2f4552cd

* Add custom checks for EventDispatcher in @SimpleEvent

Change-Id: I72a704e9f8d489aa08cefd50ca180b1130b3e5fa

appinventor/build.xml

@@ -129,6 +129,35 @@
     </javadoc>
   </target>
 
+  <target name="checkstyle-all">
+    <java classname="com.puppycrawl.tools.checkstyle.Main" fork="true">
+      <classpath>
+        <pathelement path="lib/checkstyle/checkstyle.jar"/>
+        <pathelement path="lib/checkstyle/appinventor-checks.jar"/>
+      </classpath>
+      <arg value="-c"/>
+      <arg value="lib/checkstyle/appinventor-checks.xml"/>
+      <arg value="appengine/src"/>
+      <arg value="appengine/tests"/>
+      <arg value="blocklyeditor/src"/>
+      <arg value="blocklyeditor/tests"/>
+      <arg value="buildserver/src"/>
+      <arg value="buildserver/tests"/>
+      <arg value="common/src"/>
+      <arg value="common/tests"/>
+      <arg value="components/src"/>
+      <arg value="components/tests"/>
+    </java>
+  </target>
+
+  <target name="checkstyle">
+    <property name="commit" value="HEAD"/>
+    <exec executable="misc/checkstyle/checkstyle-git.py"
+          failonerror="true">
+      <arg value="${commit}"/>
+    </exec>
+  </target>
+
   <target name="clean">
     <ant inheritAll="false" useNativeBasedir="true" dir="appengine" target="clean"/>
     <ant inheritAll="false" useNativeBasedir="true" dir="blocklyeditor" target="clean"/>

appinventor/misc/checkstyle/checkstyle-git.py

+#!/usr/bin/env python3
+import subprocess
+from io import StringIO
+from re import compile
+import os
+import sys
+
+
+parent_commit = 'HEAD' if len(sys.argv) < 2 else sys.argv[1]
+checkstyle_pattern = compile(r'^\[(?P<severity>[^\]]*)\] (?P<filename>[^:]*):(?P<line>[0-9]*):(?P<message>.*)'
+                             r' \[(?P<rule>[^\]]*)\]$')
+compile(r'^\[(?P<severity>[^\]]*)\]')
+basedir = os.getcwd() if os.path.exists('build.xml') else os.path.join(os.getcwd(), 'appinventor')
+
+
+def checkstyle(current_file):
+    return StringIO(subprocess.check_output(['java', '-cp',
+                                             'lib/checkstyle/checkstyle.jar:lib/checkstyle/appinventor-checks.jar',
+                                             'com.puppycrawl.tools.checkstyle.Main', '-c',
+                                             'lib/checkstyle/appinventor-checks.xml', current_file],
+                                            encoding='utf-8', cwd=basedir))
+
+
+def check_chunks(checkstyle_output, chunks):
+    """
+
+    :param checkstyle_output:
+    :param chunks:
+    :type chunks: list[(int, int)]
+    :return:
+    """
+    success = True
+    i = 0
+    for line in checkstyle_output:
+        match = checkstyle_pattern.match(line.strip())
+        if match:
+            linenum = int(match.group('line'))
+            while i < len(chunks):
+                if chunks[i][0] <= linenum < chunks[i][1]:
+                    print(line.strip())
+                    success = False
+                    break
+                elif chunks[i][0] <= linenum:
+                    i += 1
+                    if i >= len(chunks):
+                        return success
+                else:
+                    break
+    return success
+
+
+def process_chunk_info(line):
+    """
+    Processes a unified diff chunk header and returns a tuple indication the start and length of the deletion and
+    addition hunks.
+
+    :param line: Unified diff chunk marker, beginning with '@@'
+    :type line: str
+    :return: a 4-tuple of deletion start, deletion length, addition start, addition length
+    :rtype: tuple[int]
+    """
+    parts = line.split(' ')
+    del_info = parts[1][1:]
+    add_info = parts[2][1:]
+    del_start, del_length = map(int, del_info.split(',')) if ',' in del_info else (int(del_info), 1)
+    add_start, add_length = map(int, add_info.split(',')) if ',' in add_info else (int(add_info), 1)
+    return del_start, del_length, add_start, add_length
+
+
+def main(parent):
+    current_file, chunk_start, chunk_length = '', 0, 0
+    checkstyle_output = None
+    chunks = []
+    passed = True
+    for line in StringIO(subprocess.check_output(['git', 'diff', '-U0', parent], encoding='utf-8')):
+        if line.startswith('diff --git'):
+            pass
+        elif line.startswith('index '):
+            pass
+        elif line.startswith('---'):
+            if '/dev/null' in line:
+                new_file = True
+            else:
+                new_file = False
+            pass
+        elif line.startswith('+++'):
+            if line.startswith('+++ /dev/null'):
+                continue  # Deleted file
+            if len(chunks) > 0 and current_file != '':
+                passed = check_chunks(checkstyle_output, chunks) and passed
+            # Handle new file
+            current_file = line[6:].strip()
+            current_file = os.path.join('..', current_file)
+            checkstyle_output = checkstyle(current_file)
+            chunks = []
+        elif line.startswith('@@'):
+            # Handle chunk
+            del_start, del_length, add_start, add_length = process_chunk_info(line)
+            if add_length > 0:
+                # Addition or replacement
+                chunks.append((add_start, add_start + add_length))
+            else:
+                # Code removal. Check next line to ensure it didn't introduce an error
+                chunks.append((del_start, del_start + 1))
+
+    if len(chunks) > 0:
+        passed = check_chunks(checkstyle_output, chunks) and passed
+
+    return passed
+
+
+if __name__ == '__main__':
+    if 'BYPASS_CHECKSTYLE' in os.environ:
+        sys.exit(0)
+    if main(parent_commit):
+        sys.exit(0)
+    else:
+        sys.exit(1)