Fix keyCommandsDoc raises UnboundLocalError for a malformed settingsSection command

[JulienCochuyt]

Link to issue number:

Found while working on PR #11297

Summary of the issue:

A malformed settingsSection command in userGuide.t2t can lead to the following misleading output:

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `source' is up to date.
Generating user_docs\en\keyCommands.t2t
scons: *** [user_docs\en\keyCommands.t2t] UnboundLocalError : local variable 'key' referenced before assignment
Traceback (most recent call last):
  File "C:\dev\workspace\nvda\include\scons\src\engine\SCons\Action.py", line 1209, in execute
    result = self.execfunction(target=target, source=rsources, env=env)
  File "C:\dev\workspace\nvda\SConstruct", line 80, in <lambda>
    lambda target,source,env: not keyCommandsDoc.KeyCommandsMaker(source[0].path,target[0].path).make(),
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 123, in make
    self._make()
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 137, in _make
    self._command(**m.groupdict())
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 184, in _command
    self._handleSetting()
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 263, in _handleSetting
    raise KeyCommandsError("%d, setting command: The keyboard shortcuts must be followed by a blank line. Multiple keys must be included in a table. Erroneous key: %s" % (self._lineNum, key))
UnboundLocalError: local variable 'key' referenced before assignment
scons: building terminated because of errors.

Explanation: The processing of the next setting command asserts there is at least one keyboard layout and thus misses to initialize the key variable if the previous settingsSection command did not define enough columns.

Description of how this pull request fixes the issue:

Fail early when the malformed settingsSection command is processed, leading to this more informative output:

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `source' is up to date.
Generating user_docs\en\keyCommands.t2t
scons: *** [user_docs\en\keyCommands.t2t] KeyCommandsError : 1520, settingsSection command must specify the header row for a table summarising the settings
Traceback (most recent call last):
  File "C:\dev\workspace\nvda\include\scons\src\engine\SCons\Action.py", line 1209, in execute
    result = self.execfunction(target=target, source=rsources, env=env)
  File "C:\dev\workspace\nvda\SConstruct", line 80, in <lambda>
    lambda target,source,env: not keyCommandsDoc.KeyCommandsMaker(source[0].path,target[0].path).make(),
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 123, in make
    self._make()
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 137, in _make
    self._command(**m.groupdict())
  File "C:\dev\workspace\nvda\keyCommandsDoc.py", line 185, in _command
    f"{self._lineNum}, settingsSection command must specify the header row for a table"
keyCommandsDoc.KeyCommandsError: 1520, settingsSection command must specify the header row for a table summarising the settings
scons: building terminated because of errors.

Testing performed:

Ran scons source user_docs with and without a malformed settingsSection command.
Ensured the produced keyCommands.t2t is not affected by this change when the input is valid.

Known issues with pull request:

Change log entry:

I guess this change does not deserve a change log entry.