We add a new class CSSVariableResolver whose job is to take the
inherited computed variables and the specified variable declarations and
to perform cycle removal and resolution of the variables, storing the
result in the CSSVariableValues object on an nsStyleVariables. We use
CSSVariableResolver in nsRuleNode::ComputeVariablesData.
The variable resolver does this:
1. Asks the CSSVariableValues and CSSVariableDeclarations objects
to add their variables to it.
2. Calls in to a new nsCSSParser function
EnumerateVariableReferences that informs the resolver which
other variables a given variable references, and by doing so,
builds a graph of variable dependencies.
3. Removes variables involved in cyclic references using Tarjan's
strongly connected component algorithm, setting those variables
to have an invalid value.
4. Calls in to a new nsCSSParser function ResolveVariableValue
to resolve the remaining valid variables by substituting variable
references.
We extend nsCSSParser::ParseValueWithVariables to take a callback
function to be invoked when encountering a variable reference. This
lets EnumerateVariableReferences re-use ParseValueWithVariables.
CSSParserImpl::ResolveValueWithVariableReferences needs different
error handling behaviour from ParseValueWithVariables, so we don't
re-use it.
CSSParserImpl::AppendImpliedEOFCharacters is used to take the
value returned from nsCSSScanner::GetImpliedEOFCharacters while
resolving variable references that were declared using custom
properties that encountered EOF before being closed properly.
The SeparatorRequiredBetweenTokens helper function in nsCSSParser.cpp
implements the serialization rules in CSS Syntax Module Level 3:
https://dvcs.w3.org/hg/csswg/raw-file/3479cdefc59a/css-syntax/Overview.html#serialization
This adds a CSSVariableDeclarations object to nsRuleData and adds a
MapRuleInfoInto function to CSSVariableDeclarations so the can copy
variable declarations into a nsRuleData's object. We call that from
Declaration::Map{Normal,Important}RuleInfoInto.
We make HasImportantData return true if we have important variables
but no important non-custom properties on a declaration, since that
is used to determine whether we have a rule node for important
declarations. This means MapImportantRuleInfoInto can no longer
assume that mImportantData is non-null.
Patch co-authored by Emmanuele Bassi <ebassi@gmail.com>
This defines a CSSVariableDeclarations class that holds a set of
variable declarations. This is at the specified value stage, so values
can either be 'initial', 'inherit' or a token stream (which is what you
normally have). The variables are stored in a hash table. Although
it's a bit of a hack, we store 'initial' and 'inherit' using special
string values that can't be valid token streams (we use "!" and ";").
Declaration objects now can have two CSSVariableDeclarations objects
on them, to store normal and !important variable declarations. So that
we keep preserving the order of declarations on the object, we inflate
mOrder to store uint32_ts, where values from eCSSProperty_COUNT onwards
represent custom properties. mVariableOrder stores the names of the
variables corresponding to those entries in mOrder.
We also add a new nsCSSProperty value, eCSSPropertyExtra_variable, which
is used to represent any custom property name.
nsCSSProps::LookupProperty can return this value.
The changes to nsCSSParser are straightforward. Custom properties
are parsed and checked for syntactic validity (e.g. "var(a,)" being
invalid) and stored on the Declaration. We use nsCSSScanner's
recording ability to grab the unparsed CSS string corresponding to
the variable's value.
Cameron McCormack