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authorSebastian Luther <SebastianLuther@gmx.de>2010-06-15 23:15:30 +0200
committerZac Medico <zmedico@gentoo.org>2010-08-12 01:17:24 -0700
commit6736994827eb295593842afe1a2b159ee84b4a4f (patch)
treeb2611379a1f5fd1b13d168420872936bb1d6db97
parent65df7762b61ef6072ad48a159e0f35d80a5146dc (diff)
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slot_collision_handler: Add more documentation
-rw-r--r--pym/_emerge/resolver/slot_collision.py59
1 files changed, 59 insertions, 0 deletions
diff --git a/pym/_emerge/resolver/slot_collision.py b/pym/_emerge/resolver/slot_collision.py
index f4d5411b1..8b499ec00 100644
--- a/pym/_emerge/resolver/slot_collision.py
+++ b/pym/_emerge/resolver/slot_collision.py
@@ -10,7 +10,66 @@ from portage.versions import cpv_getversion, vercmp
class slot_conflict_handler(object):
"""This class keeps track of all slot conflicts and provides
an interface to get possible solutions.
+
+ How it works:
+ If two packages have been pulled into a slot, one needs to
+ go away. This class focuses on cases where this can be achieved
+ with a change in USE settings.
+
+ 1) Find out if what causes a given slot conflict. There are
+ three possibilities:
+
+ a) One parent needs foo-1:0 and another one needs foo-2:0,
+ nothing we can do about this. This is called a 'version
+ based conflict'.
+
+ b) All parents of one of the conflict packages could use
+ another conflict package. This is called an 'unspecific
+ conflict'. This should be caught by the backtracking logic.
+ Ask the user to enable -uN (if not already enabled). If -uN is
+ enabled, this case is treated in the same way as c).
+
+ c) Neither a 'version based conflict' nor an 'unspecific
+ conflict'. Ignoring use deps would result result in an
+ 'unspecific conflict'. This is called a 'specific conflict'.
+ This is the only conflict we try to find suggestions for.
+
+ 2) Computing suggestions.
+
+ Def.: "configuration": A list of packages, containing exactly one
+ package from each slot conflict.
+
+ We try to find USE changes such that all parents of conflict packages
+ can work with a package in the configuration we're looking at. This
+ is done for all possible configurations, except if the 'all-ebuild'
+ configuration has a suggestion. In this case we immediately abort the
+ search.
+ For the current configuration, all use flags that are part of violated
+ use deps are computed. This is done for every slot conflict on its own.
+
+ Def.: "solution (candidate)": An assignment of "enabled" / "disabled"
+ values for the use flags that are part of violated use deps.
+
+ Now all involved use flags for the current configuration are known. For
+ now they have an undetermined value. Fix their value in the
+ following cases:
+ * The use dep in the parent atom is unconditional.
+ * The parent package is 'installed'.
+ * The conflict package is 'installed'.
+
+ USE of 'installed' packages can't be changed. This always requires an
+ non-installed package.
+
+ During this procedure, contradictions may occur. In this case the
+ configuration has no solution.
+
+ Now generate all possible solution candidates with fixed values. Check
+ if they don't introduce new conflicts.
+
+ We have found a valid assignment for all involved use flags. Compute
+ the needed USE changes and prepare the message for the user.
"""
+
def __init__(self, slot_collision_info, all_parents, myopts):
self.myopts = myopts
self.debug = "--debug" in myopts