feat: add rule dependencies

If extensions are not installed, it might happen that rules are
executing and try to read tables that do not exist. To handle this, it
is now possible to provide a dictionary of required extensions and
version and rules will only be executed if all required extensions are
installed.

.github/workflows/checks.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install pylint psycopg2
+        pip install pylint psycopg2 packaging
     - name: Analysing the code with pylint
       run: |
         pylint $(git ls-files '*.py')

setup.py

@@ -69,7 +69,8 @@ def get_version(rel_path: str) -> str:
         "Programming Language :: Python :: 3 :: Only",
     ],
     install_requires=[
-          'psycopg2',
+        'psycopg2',
+        'packaging',
       ],
     entry_points={
         "console_scripts": [

src/doctor/__init__.py

@@ -21,6 +21,7 @@
 from textwrap import dedent, fill
 from os.path import dirname, basename, isfile, join
 from abc import ABC
+from packaging.version import parse
 
 import psycopg2
 
@@ -54,14 +55,31 @@ class Rule(ABC):
       optional field. If no field is given, the value of the "message"
       field will be used.
 
+    dependencies: Dictionary with dependencies on packages and what
+    versions that are required.
+
     """
 
+    def get_versions(self, conn):
+        """Get extension versions."""
+        with conn.cursor() as cursor:
+            cursor.execute("SELECT extname, extversion FROM pg_extension WHERE extname IN %s",
+                           (tuple(self.dependencies.keys()),)) # pylint: disable=E1101
+            return {row[0]:row[1] for row in cursor}
+
+
     def execute(self, conn, text):
         """Execute rule and return one string for each mismatching object."""
-        cursor = conn.cursor()
-        cursor.execute(self.query) # pylint: disable=E1101
-        return [text.format(**kwrds) for kwrds in cursor]
-
+        with conn.cursor() as cursor:
+            # Check that all dependencies are met. If not, we do not
+            # execute the rule.
+            if hasattr(self, 'dependencies'):
+                versions = self.get_versions(conn)
+                for ext,req in self.dependencies.items(): # pylint: disable=E1101
+                    if ext not in versions or parse(req) > parse(versions[ext]):
+                        return []
+            cursor.execute(self.query) # pylint: disable=E1101
+            return [text.format(**kwrds) for kwrds in cursor]
 
 def register(cls):
     """Register a rule."""

src/doctor/rules/compression.py

@@ -14,8 +14,6 @@
 
 """Rules for compressed hypertables."""
 
-from dataclasses import dataclass
-
 import doctor
 
 LINEAR_QUERY = """
@@ -30,7 +28,6 @@
 """
 
 @doctor.register
-@dataclass
 class LinearSegmentby(doctor.Rule):
     """Detect segmentby column for compressed table."""
 
@@ -44,6 +41,9 @@ class LinearSegmentby(doctor.Rule):
         " with the number of rows of the table."
 
     )
+    dependencies: dict = {
+        'timescaledb': '1.0'
+    }
 
 POINTLESS_QUERY = """
 SELECT format('%I.%I', schema_name, table_name)::regclass AS relation, s.attname
@@ -57,7 +57,6 @@ class LinearSegmentby(doctor.Rule):
 """
 
 @doctor.register
-@dataclass
 class PointlessSegmentBy(doctor.Rule):
     """Detect pointless segmentby column in compressed table."""
 
@@ -69,3 +68,6 @@ class PointlessSegmentBy(doctor.Rule):
         "Column '{attname}' in hypertable '{relation}' as segment-by column is pointless"
         " since it contains a single value."
     )
+    dependencies: dict = {
+        'timescaledb': '1.0'
+    }

src/doctor/rules/hypertable.py

@@ -14,8 +14,6 @@
 
 """Rules for hypertables."""
 
-from dataclasses import dataclass
-
 import doctor
 
 CANDIDATE_QUERY = """
@@ -49,7 +47,6 @@
 """
 
 @doctor.register
-@dataclass
 class HypertableCandidate(doctor.Rule):
     """Detect candidate hypertable."""
 
@@ -72,9 +69,11 @@ class HypertableCandidate(doctor.Rule):
 """
 
 @doctor.register
-@dataclass
 class ChunkPermissions(doctor.Rule):
     """Detect bad chunk permissions."""
 
     query: str = PERMISSION_QUERY
     message: str = "Chunk '{chunk}' have different permissions from hypertable '{hypertable}'."
+    dependencies: dict = {
+        'timescaledb': '1.0'
+    }