144899 - nsHTMLStyleSheet table rules code looks inefficient

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect, P3)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

I just noticed all the code in nsHTMLStyleSheet that was added for bug 41262. 
This code does a bunch of things less efficiently than it should be:
 * it looks to me like it prevents any table style data from being cached in the
rule tree, even when the rules attribute is not present
 * it does stuff in the post resolve callback that really should be done earlier
so that it doesn't mess up the cascade

I suspect that what should be done here is:
 * rather than mapping the "rules" attribute into style on the table's style
context, do a GetAttribute on the table in RulesMatching and add the appropriate
rule(s) only if needed.
 * rather than using a single rule object, create one rule object for each table
element that has a "rules" attribute (or whatever attributes are currently being
mapped into tableData->mRules, and either cache this straight on the table
element or use a hashtable.  This allows us to get the benefits of the rule tree
even when the rules are needed.
 * Do the work normal MapRuleInfoInto phase rather than the post resolve callback.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Note that the rules also should be immutable to satisfy the contract of the
nsIStyleRule interface (bug 188803).

Comment 2

[Bernd]

the code is question got removed in bug 43178