Add a config param to avoid Python exception checking overheads (#26573)

Adds `Python.checkExceptions` (on by default), which allows users to
turn off the exception checking to avoid overhead.

This PR also includes a few other cleanups and adds a future for
#26579

- [x] `start_test test/library/packages/Python` 
- [x] `start_test test/library/packages/Python --compopts
-scheckExceptions=false`
- this has 1 expected failure of `argPassingTest`, which tests
exceptions

Future work:
- It would be nice to support this as a per-interpreter param as well,
but that opens us up to issues with generics and classes. So for now
thats a todo/nice-to-have

[Reviewed by @DanilaFe]

modules/packages/Python.chpl

@@ -230,8 +230,28 @@ module Python {
   private use CWChar;
   private use OS.POSIX only getenv;
 
+  /*
+    Use 'objgraph' to detect memory leaks in the Python code. Care should be
+    taken when interpreting the output of this flag, not all memory leaks are
+    under Chapel's control. For example, printing a Python list leaks memory
+    according to 'objgraph'. Furthermore, some memory is still held when until
+    the interpreter is closed, like the module import cache.
+  */
   config const pyMemLeaks = false;
 
+  /*
+    Check for exceptions after each Python API call. This is important for
+    correctness, but may have a performance impact.
+
+    .. warning::
+
+       While turning this flag off may improve performance, it may also lead to
+       segmentation faults and other undefined behavior. This flag should only
+       be turned off if you are certain that no exceptions will be thrown by
+       the Python code, or if a hard crash is acceptable.
+  */
+  config param checkExceptions = true;
+
   // TODO: this must be first to avoid use-before-def, but that makes it first in the docs
   // is there a way to avoid this?
   /* Represents the python NoneType */
@@ -246,14 +266,6 @@ module Python {
   /* Represents the python value 'None' */
   const None = new NoneType();
 
-
-  @chpldoc.nodoc
-  enum codeKind {
-    source,
-    bytecode,
-    pickle
-  }
-
   private proc getOsPathSepHelper(interp: borrowed Interpreter): string throws {
     var os = PyImport_ImportModule("os");
     interp.checkException();
@@ -276,6 +288,18 @@ module Python {
        Do not create more than one instance of this class.
   */
   class Interpreter {
+
+    // TODO: add ability to override the global checkExceptions
+    // currently blocked by https://github.com/chapel-lang/chapel/issues/26579
+    /*
+      Whether to check for exceptions after each Python API call. This is
+      important for correctness, but may have a performance impact.
+
+      See :config:`Python.checkExceptions` and
+      :method:`Interpreter.checkException` for more information.
+    */
+    // param checkExceptions: bool = Python.checkExceptions;
+
     @chpldoc.nodoc
     var converters: List.list(owned TypeConverter);
     @chpldoc.nodoc
@@ -553,9 +577,9 @@ module Python {
          most users should not need to call this method directly.
     */
     inline proc checkException() throws {
-      var exc = chpl_PyErr_GetRaisedException();
-      if exc {
-        throw PythonException.build(this, exc);
+      if Python.checkExceptions {
+        var exc = chpl_PyErr_GetRaisedException();
+        if exc then throw PythonException.build(this, exc);
       }
     }
 
@@ -1056,7 +1080,7 @@ module Python {
         Py_DECREF(this.obj);
     }
 
-    proc check() throws do this.interpreter.checkException();
+    inline proc check() throws do this.interpreter.checkException();
 
     /*
       Returns the :type:`~CTypes.c_ptr` to the underlying Python object.
@@ -1227,7 +1251,7 @@ module Python {
     */
     proc init(interpreter: borrowed Interpreter,
               in modName: string, in moduleContents: string) throws {
-      super.init(interpreter, nil: PyObjectPtr);
+      super.init(interpreter, nil: PyObjectPtr, isOwned=true);
       this.modName = modName;
       init this;
       this.obj = interpreter.compileModule(moduleContents, modName);
@@ -1238,7 +1262,7 @@ module Python {
     */
     proc init(interpreter: borrowed Interpreter,
               in modName: string, in moduleBytecode: bytes) throws {
-      super.init(interpreter, nil: PyObjectPtr);
+      super.init(interpreter, nil: PyObjectPtr, isOwned=true);
       this.modName = modName;
       init this;
       this.obj = interpreter.compileModule(moduleBytecode, modName);
@@ -1264,7 +1288,7 @@ module Python {
       this.fnName = fnName;
     }
     proc init(interpreter: borrowed Interpreter, in lambdaFn: string) throws {
-      super.init(interpreter, nil:PyObjectPtr, isOwned=true);
+      super.init(interpreter, nil: PyObjectPtr, isOwned=true);
       this.fnName = "<anon>";
       init this;
       this.obj = interpreter.compileLambda(lambdaFn);

test/classes/generic/nonGenericSubclassGenericSuperclass.bad

@@ -0,0 +1,8 @@
+nonGenericSubclassGenericSuperclass.chpl:19: internal error: RES-FUN-ION-2796 chpl version 2.4.0 pre-release (9ab0d960101)
+Note: This source location is a guess.
+
+Internal errors indicate a bug in the Chapel compiler,
+and we're sorry for the hassle.  We would appreciate your reporting this bug --
+please see https://chapel-lang.org/bugs.html for instructions.  In the meantime,
+the filename + line number above may be useful in working around the issue.
+

test/classes/generic/nonGenericSubclassGenericSuperclass.chpl

@@ -0,0 +1,19 @@
+class Generic {
+  param x = 1;
+}
+
+class Parent {
+  var x: borrowed Generic(?);
+  proc init(x: borrowed Generic(?)) {
+    this.x = x;
+  }
+}
+
+class Child: Parent(?) {
+  proc init(x: borrowed Generic(?)) {
+    super.init(x);
+  }
+}
+
+var g = new Generic();
+var c = new Child(g);

test/classes/generic/nonGenericSubclassGenericSuperclass.future

@@ -0,0 +1,2 @@
+bug: inheriting from a generic class in a non-generic subclass
+#26579

test/library/packages/Python/correctness/noExceptions.bad

@@ -0,0 +1,4 @@
+noExceptions.chpl:18: error: unresolved call 'Interpreter.init(0)'
+$CHPL_HOME/modules/packages/Python.chpl:nnnn: note: this candidate did not match: Interpreter.init()
+noExceptions.chpl:18: note: because call includes 1 argument
+$CHPL_HOME/modules/packages/Python.chpl:nnnn: note: but function can only accept 0 arguments

test/library/packages/Python/correctness/noExceptions.chpl

@@ -0,0 +1,32 @@
+use Python;
+
+var hello = """
+print('Hello, World!')
+""";
+var hello_raise = """
+raise Exception('Hello, World!')
+""";
+
+// use default checking
+{
+  var interp = new Interpreter();
+  var mod = new Module(interp, 'hello', hello);
+}
+
+// explicitly use no checking, blocked by https://github.com/chapel-lang/chapel/issues/26579
+{
+  var interp = new Interpreter(false);
+  var mod = new Module(interp, 'hello', hello);
+}
+
+// explicitly use checking, blocked by https://github.com/chapel-lang/chapel/issues/26579
+{
+  var interp = new Interpreter(true);
+  try {
+    var mod = new Module(interp, 'hello', hello_raise);
+  } catch e: PythonException {
+    writeln("Caught exception: ", e.message());
+  } catch {
+    writeln("Caught unknown exception");
+  }
+}

test/library/packages/Python/correctness/noExceptions.compopts

@@ -0,0 +1 @@
+-scheckExceptions=false

test/library/packages/Python/correctness/noExceptions.future

@@ -0,0 +1 @@
+feature request: ability to set override the global checkExceptions

test/library/packages/Python/correctness/noExceptions.good

@@ -0,0 +1,3 @@
+Hello, World!
+Hello, World!
+Caught exception: Hello, World!

test/library/packages/Python/correctness/noExceptions.prediff

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+$CHPL_HOME/util/test/prediff-obscure-module-linenos $@