SettingsEditor segfaults reading a bound method off a field

songformatter now COMPILES and RUNS as far as building its GUI, and dies here:

class SettingsEditor(tk.Frame):        # settings.py:110
    def __init__(self, parent):
        super().__init__(parent)
        ...
        self.canvas = tk.Canvas(self, highlightthickness=0)     # 122 — fine
        self.scrollbar = tk.Scrollbar(self, orient="vertical",
                                      command=self.canvas.yview)  # 123 — SIGSEGV

Split into yv = self.canvas.yview / Scrollbar(..., command=yv), the crash is on the FIRST line: capturing the bound method, not passing it.

Not yet reproduced in isolation

The same shape outside the application works — a tk.Frame subclass whose __init__ builds a Canvas into a field, reads self.canvas.yview into a local and hands it to a Scrollbar, with configparser and the reportlab shim's rival Canvas class both linked. So something else about settings.py's environment decides it. Worth trying next:

• what self.canvas's FIELD type resolves to in that class (the field pre-pass picks a class by name, and reportlab's Canvas is a rival — the [[decide-class-namespace-scoping]] family). A field typed as the wrong Canvas would make .yview read a method that is not there.
• whether the crash needs the ~60 later widgets in populate_frame to exist (the class is large; the repro is small).

How to see it

./compiler/pascal26 -Fu<app> <app>/se3.py /tmp/se3     # se3.py: SettingsEditor(root)
DISPLAY=:99 /tmp/se3

with se3.py = import tkinter as tk; from settings import SettingsEditor; root = tk.Tk(); SettingsEditor(root).

Gate

make test-nilpy plus a .npy reproducing whatever the isolation turns out to need, diffed against CPython — and songformatter's window actually opening under Xvfb.

Reproduced in isolation, and it is not the rival Canvas (2026-07-29)

The application environment turned out to be irrelevant. No reportlab, no configparser, no 60 widgets — the class only has to live in an imported .py module:

# m6.py — a MODULE
import tkinter as tk

class A(tk.Frame):
    def __init__(self, parent):
        super().__init__(parent)
        self.canvas = tk.Canvas(self, highlightthickness=0)
        print("field set")                       # prints
        self.canvas.create_line(0, 0, 5, 5)
        print("field METHOD CALL ok")            # prints
        yv = self.canvas.yview
        print("field CAPTURE ok")                # SIGSEGV before this

# t6.py — the program
import tkinter as tk
from m6 import A
root = tk.Tk(); A(root); print("done")

The same class pasted into the MAIN file runs clean. That pair of facts settles the two open questions in this ticket:

• a method call on the same field works, so self.canvas's field type resolves correctly — the rival reportlab Canvas ([[decide-class-namespace-scoping]]) is not involved;
• the later widgets are not needed either.

Cause

parser.inc, the bound-method-value arm:

if isNilPy and (CurrentUnitIdx < 0) and (CurTok.Kind <> tkLParen) and ...

CurrentUnitIdx < 0 means the main program only. A .py module compiles with CurrentUnitIdx >= 0, so obj.method as a VALUE was not recognised there and fell through to the call path, producing a call through a non-method — the segfault.

Fix

The gate becomes ((CurrentUnitIdx < 0) or PyExprMode). ParsePyUnit turns PyExprMode on for a module body and Pascal RTL units never have it, so it expresses the rule the arm actually wants: NilPy USER code, main program or module.

Verified on the minimal module repro, on the ticket's original inline form (command=self.canvas.yview passed straight to Scrollbar) and on a SettingsEditor-shaped class; the main-file case still works. test/test_nilpy_bound_method_in_module.npy (+ test/boundfield_mod.py) covers capture off a field and off self inside a module, diffed against CPython.

Six SIBLING gates of the same shape are wrong in the same way and are filed together as [[bug-nilpy-object-reclamation-disabled-inside-py-modules]] — they are self-consistent (no zero-init AND no release), so they leak rather than crash, and they must move as a set.

Log

• 2026-07-29 — resolved, commit HEAD.