ENB: Leo's startup order

[Edward K. Ream]

Recent ENBs have discussed two implicit graphs of import dependencies. Leo's fast pylint project, #3852, will likely sidestep such issues.

However, I laboriously calculated Leo's startup dependencies by hand. I'll present them here.

The level of a Leo file is:

- zero if the file imports no other Leo files.

- one more than the maximum level of all the Leo files otherwise.

Core files

Level 0: no imports at the top level.

leo.core.leoApp

leo.core.leoBridge

leo.core.leoColor

leo.core.leoFastRedraw

leo.core.leoGlobals

leo.core.leoImport

leo.core.leoPymacs

leo.core.leoQt

leo.core.leoTokens

leo.core.leoVersion

leo.core.signal_manager

leo.core.tracing_utils

Level 1: import only leoGlobals at the top level.

leo.core.leoAst

leo.core.leoCache

leo.core.leoChapters

leo.core.leoCompare

leo.core.leoDebugger

leo.core.leoExternalFiles

leo.core.leoFind

leo.core.leoHistory

leo.core.leoIPython

leo.core.leoKeys

leo.core.leoMarkup

leo.core.leoMenu

leo.core.leoNodes

leo.core.leoPersistence

leo.core.leoPlugins

leo.core.leoRope

leo.core.leoRst

leo.core.leoSessions

leo.core.leoShadow

leo.core.leoTips

leo.core.leoVim

Level 1: import only level 0 modules at the top level.

leo.core.leoBackground

    from leo.core import leoGlobals as g

    from leo.core.leoQt import QtCore

leo.core.leoColorizer

    from leo.core import leoGlobals as g

    from leo.core.leoColor import leo_color_database

    from leo.core.leoQt import ...

leo.plugins.modScripting

    from leo.core import leoGlobals as g

    from leo.core import leoColor

    from leo.core import leoGui

leo.core.leoPrinting

    from leo.core import leoGlobals as g

    from leo.core.leoQt import ...

leo.core.leoTest2

    from leo.core import leoGlobals as g

    from leo.core import leoApp

leo.core.runLeo

    from leo.core import leoGlobals as g

    from leo.core import leoApp

Level 2: import only level 0 or 1 modules at the top level.

leo.core.leoAtFile

    from leo.core import leoGlobals as g

    from leo.core import leoNodes

leo.core.leoBeautify

    from leo.core import leoGlobals as g

    from leo.core import leoAst

leo.core.leoCommands: # ctor instantiates all sub-commanders!

    from leo.core import leoGlobals as g

    from leo.core import leoNodes

leo.core.leoConfig

    from leo.core import leoGlobals as g

    from leo.plugins.mod_scripting import build_rclick_tree

leo.core.leoFileCommands

    from leo.core import leoGlobals as g

    from leo.core import leoNodes

Level 3: import only modules of levels 0, 1, or 2 at the top level.

leo.core.leoFrame

    from leo.core import leoGlobals as g

    from leo.core import leoColorizer

    from leo.core import leoMenu

    from leo.core import leoNodes

leo.core.leoserver

    from leo.core.leoCommands import Commands as Cmdr

    from leo.core.leoNodes import Position, VNode

    from leo.core.leoGui import StringFindTabManager

    from leo.core.leoExternalFiles import ExternalFilesController

leo.core.leoUndo

    from leo.core import leoGlobals as g

    from leo.core.leoFileCommands import FastRead

    from leo.core.leoNodes import Position, VNode

Level 4: import only modules of levels 0, 1, 2, or 3 at the top level.

leo.core.leoGui

    from leo.core import leoGlobals as g

    from leo.core import leoFrame

leo.core.leoclient

    from leo.core import leoGlobals as g

    from leo.core import leoserver

Command files

Level 1: import only leoGlobals at the top level.

leo.commands.baseCommands

leo.commands.checkerCommands

leo.commands.editCommands

leo.commands.commanderHelpCommands

leo.commands.gotoCommands

Level 1: import only level 0 modules at the top level.

leo.commands.commanderFileCommands

    from leo.core import leoGlobals as g

    from leo.core import leoImport

    

Level 2: import only leoGlobals and leo.commands.baseCommands

leo.commands.bufferCommands

leo.commands.controlCommands

leo.commands.debugCommands

leo.commands.editCommands

leo.commands.helpCommands

leo.commands.keyCommands

leo.commands.killBufferCommands

leo.commands.rectangleCommands

leo.commands.spellCommands

Level 2: import only level 0 or 1 modules at the top level.

leo.commands.abbrevCommands

    from leo.core import leoGlobals as g

    from leo.core import leoNodes

    from leo.commands.baseCommands import BaseEditCommandsClass

leo.commands.commanderOutlineCommands

    from leo.core import leoGlobals as g

    from leo.core import leoNodes

    from leo.core import leoFileCommands

    

Level 3: import only modules of levels 0, 1, or 2 at the top level.

leo.commands.convertCommands

    from leo.core import leoGlobals as g

    from leo.core import leoBeautify

    from leo.commands.baseCommands import BaseEditCommandsClass

leo.commands.editFileCommands

    from leo.core import leoGlobals as g

    from leo.core import leoCommands

    from leo.commands.baseCommands import BaseEditCommandsClass

Summary

The tables above implicitly reveal Leo's import order during startup. Leo's Commands class imports all of Leo's sub-commanders when Leo creates the first commander. 

Deferring the imports of sub-commanders breaks all potential circular imports. Devs should be aware of this design. It hasn't changed in decades.

Edward