From 998ebe4414b4ceff8fdbc180cf06f1b4b6bad933 Mon Sep 17 00:00:00 2001
From: dgelessus <dgelessus@users.noreply.github.com>
Date: Tue, 18 Aug 2020 16:37:23 +0200
Subject: [PATCH] Check Python runtime version using tuple comparison

The previous implementation used pkg_resources.parse_version to parse
the kaitaistruct module's __version__ string. Unfortunately, importing
pkg_resources is relatively slow, which had a noticeable performance
impact on every ksc-generated parser.

The new implementation uses the newly added kaitaistruct.API_VERSION
attribute, which stores the runtime version as a tuple of ints. In this
format the version information can be compared directly without having
to parse it from a string first. This allows removing the import of
pkg_resources, which fixes the performance problem.

Part of the fix for kaitai-io/kaitai_struct#804.
---
 .../scala/io/kaitai/struct/format/KSVersion.scala  |  9 +++++++++
 .../kaitai/struct/languages/PythonCompiler.scala   | 14 ++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/shared/src/main/scala/io/kaitai/struct/format/KSVersion.scala b/shared/src/main/scala/io/kaitai/struct/format/KSVersion.scala
index 766bd891e..43e1bd369 100644
--- a/shared/src/main/scala/io/kaitai/struct/format/KSVersion.scala
+++ b/shared/src/main/scala/io/kaitai/struct/format/KSVersion.scala
@@ -53,6 +53,15 @@ case class KSVersion(nums: List[Int]) extends Ordered[KSVersion] {
     val v1 :: v2 :: v3 :: _ = nums ++ List.fill(3 - nums.size)(0)
     "%d.%03d_%03d".format(v1, v2, v3)
   }
+
+  /**
+    * Dumps a version as a tuple of ints in Python syntax,
+    * that is 1.2.3 becomes "(1, 2, 3)".
+    * There are no limitations on the number of version components or the range
+    * of values for each component.
+    * @return version as a tuple of ints in Python syntax
+    */
+  def toPythonTuple: String = nums.mkString("(", ", ", ")")
 }
 
 object KSVersion {
diff --git a/shared/src/main/scala/io/kaitai/struct/languages/PythonCompiler.scala b/shared/src/main/scala/io/kaitai/struct/languages/PythonCompiler.scala
index bf5a3caaa..10d3065ca 100644
--- a/shared/src/main/scala/io/kaitai/struct/languages/PythonCompiler.scala
+++ b/shared/src/main/scala/io/kaitai/struct/languages/PythonCompiler.scala
@@ -43,7 +43,6 @@ class PythonCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
     outHeader.puts(s"# $headerComment")
     outHeader.puts
 
-    importList.add("from pkg_resources import parse_version")
     importList.add("import kaitaistruct")
     importList.add(s"from kaitaistruct import $kstructName, $kstreamName, BytesIO")
 
@@ -52,9 +51,16 @@ class PythonCompiler(typeProvider: ClassTypeProvider, config: RuntimeConfig)
 
     // API compatibility check
     out.puts(
-      "if parse_version(kaitaistruct.__version__) < parse_version('" +
-        KSVersion.minimalRuntime +
-        "'):"
+      // The API_VERSION tuple attribute was introduced in version 0.9 of the
+      // Python runtime. Runtime version 0.8 and older only have a __version__
+      // attribute that stores the version in string form.
+      // We don't need to include any complex handling for runtimes that don't
+      // have the API_VERSION attribute - we know that such a runtime must have
+      // version 0.8 or older, which means that it is incompatible with code
+      // generated by newer compiler versions.
+      "if getattr(kaitaistruct, 'API_VERSION', (0, 8)) < " +
+        KSVersion.minimalRuntime.toPythonTuple +
+        ":"
     )
     out.inc
     out.puts(