We stop on mine hits only when they're fatal. Has always been that
way. When interdiction was added in Chainsaw, it worked the same.
Empire 2 changed the commands to stop on any interdiction damage. Now
stop on any mine damage, too.
Interdiction can fail to do damage (all bombs miss), and mines can be
detected without damage (by sweeping). Perhaps we should stop then as
well. Left for another day.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
unit_move() is too big and has too many paths through its loop.
Maintenance of the (unspoken) loop invariant isn't obvious. In fact,
it isn't maintained on some paths. I found several bugs:
* We check prerequisite conditions for moving before the first move
and around prompts. When a condition becomes wrong on the move,
movement continues all the same until the next prompt. I believe
the only way this can happen is loss of crew due to hitting a mine.
* We cache ships and land units in a list of struct ulist. When a
ship or land unit gets left behind, its node is removed from the
list and freed.
We keep pointer flg pointing to the flagship in that list for
convenience. However, the pointer isn't updated until the next
prompt. It's referenced for automatic radar and all sub-commands
other than the six directions and 'h'. Use after free when such a
sub-command gets processed after a flagship change without a prompt.
Same for land units. For instance, navigating a pair of ships "jh"
where the flagship has no mobility leaves the flagship behind, then
attempts to radar automatically using the ship in the freed list
node. Likewise, marching a similar pair of land units "jl" examines
the land unit in the freed list node to figure out how to look.
* We cache mobility in the same list to support fractional mobility
during movement. Movement deducts from cached mobility and writes
the result back to the ship or land unit.
If something else charges it mobility while it's in this list, the
cache becomes stale. shp_nav() and lnd_nav() reload stale caches,
but don't run often enough. For instance, when a ship hits mines,
the mine damage makes the cache stale. If a direction or 'h'
follows directly, the stale mobility is written back, clobbering the
mine hit's mobility loss.
This mess dates back to Empire 2, where it replaced a different mess.
There may be more bugs.
unit_move()'s complex control flow makes reasoning about its loop
invariant too error-prone. Rewrite the mess instead, splitting off
sensible subroutines.
Also fixes a couple of minor annoyances:
* White-space can confuse the parser. For instance, "jg l" is
interpreted like "jgll". Fix to reject the space. Broken in commit
0c12d83, v4.3.7.
* The flagship uses radar automatically before any sub-command (since
Chainsaw), and all ships use it automatically after a move (since
4.2.2). Make them all use it before and after each sub-command,
whether it's a move or not.
* Land units don't use radar automatically. Make them use it just
like ships.
* Always report a flagship / leader change right when it happens, not
only before and after a prompt.
Left for another day, marked FIXME: BTU charging is unclean.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
When ships enter a sector with sea mines, any minesweepers sweep, then
hit mines, and finally all ships (including the minesweepers) hit
mines. Sweeping in a sector (navigate sub-command 'm') works the same
without the final step.
When land units enter a sector with land mines, any engineers sweep,
and then all land units (including the engineers) hit mines. Sweeping
in a sector (march sub-command 'm') works the same, which means
non-engineers can hit mines then. Broken in Empire 2.
Actually broken for ships too then. 4.0.17 fixed ships, but neglected
to fix land units.
Change the land unit code to work like the ship code. Fixes march
sub-command 'm' not to expose non-engineers to mines. Changes march,
attack and assault with option INTERDICT_ATT enabled to expose
engineers twice.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
When lnd_sweep() rejects an engineer for want of mobility, it removes
it from the list of units.
Can happen only when sweeping for march sub-command 'm'. Any engineer
without mobility is dropped from the march immediately. Broken in
Empire 2.
Fix lnd_sweep() to handle this case just like the others, and like
shp_sweep(): report and continue with the next list member.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
The capability to march land units spread over several sectors is
obscure and rarely useful. Accidental use is probably more frequent
than intentional use. Issues:
* Interactive prompts show only the leader's position, and give no
clue that some land units are actually elsewhere.
* Path finding is supported only when all marching land units are in
the same sector.
* In each step, the bmap is updated for the leader's radar. The bmap
is not updated around other marching land units. Already odd when
all units are in the leader's sector, and odder still when some are
elsewhere.
* Interdiction becomes rather complex. For each movement, every
sector entered is interdicted independently. This means the same
ship, land unit or plane can interdict multiple times. Interdiction
order depends on the order the code examines land units. which the
player can control. This is all pretty much undocumented.
* Complicates the code and its maintenance. Multiplies the number of
test cases needed to cover march.
I feel we're better off without this feature.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
Unlike the move command, march checks sector abandonment before every
step.
If the player declines, the last land unit stays put and is removed
from the march.
Except when sectors or land units change while we're waiting for the
player's reply. Then the last unit is not removed from the march.
This can scatter land units. Screwed up when checking for abandoning
the sector was added in 4.2.2.
Change march to work like move, and to avoid scattering land units: if
the player declines to abandon the sector, the command simply fails.
Put the check into new lnd_abandon_askyn().
Extend would_abandon() and want_to_abandon() from a single land unit
to many. Rename the latter to abandon_askyn() for consistency.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
When attempting to enter a sector with a land unit that can't go there
while the marching land units are all in the same sector, march stops
and prompts without removing the incapable land unit from the group.
If another land unit has already entered the sector, the group becomes
scattered.
This can happen when marching a mixed group of spies and non-spies
into a non-allied sector. Same for marching a mixed group of trains
and non-trains into a sector without rail, except such groups have
been disallowed since commit 36e41e5 (v4.3.7). Both screwed up when
spies and trains were added in 4.0.0
Remove the incapable land unit from the group when another land unit
can enter the sector. This avoids scattering land units.
Don't remove incapable land units when no land unit can enter the
sector. Without this, march would remove everyone and end then.
It can also happen when sectors or land units change while we're
sitting at the "Do you really want to abandon X,Y" prompt. I'm going
to fix that differently.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
Does not cover scattered navigate and march, RAILWAYS 0, enemy action
while sitting at the prompt, and interdiction.
The test exposes bugs. They're marked "BUG:" in the test input.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>
