The ones that no longer require points-to no longer import
`LegacyPointsTo`. The ones that do use the specific
`...MetricsWithPointsTo` classes that are applicable.
Moves the classes/predicates that _actually_ depend on points-to to the
`LegacyPointsTo` module, leaving behind a module that contains all of
the metrics-related stuff (line counts, nesting depth, etc.) that don't
need points-to to be evaluated.
Consequently, `Metrics` is now no longer a private import in
`python.qll`.
An example (provided by @redsun82) is the string `f"{x:=^20}"`. Parsing
this (with unnamed nodes shown) illustrates the problem:
```
module [0, 0] - [2, 0]
expression_statement [0, 0] - [0, 11]
string [0, 0] - [0, 11]
string_start [0, 0] - [0, 2]
interpolation [0, 2] - [0, 10]
"{" [0, 2] - [0, 3]
expression: named_expression [0, 3] - [0, 9]
name: identifier [0, 3] - [0, 4]
":=" [0, 4] - [0, 6]
ERROR [0, 6] - [0, 7]
"^" [0, 6] - [0, 7]
value: integer [0, 7] - [0, 9]
"}" [0, 9] - [0, 10]
string_end [0, 10] - [0, 11]
```
Observe that we've managed to combine the format specifier token `:` and
the fill character `=` in a single token (which doesn't match the `:` we
expect in the grammar rule), and hence we get a syntax error.
If we change the `=` to some other character (e.g. a `-`), we instead
get
```
module [0, 0] - [2, 0]
expression_statement [0, 0] - [0, 11]
string [0, 0] - [0, 11]
string_start [0, 0] - [0, 2]
interpolation [0, 2] - [0, 10]
"{" [0, 2] - [0, 3]
expression: identifier [0, 3] - [0, 4]
format_specifier: format_specifier [0, 4] - [0, 9]
":" [0, 4] - [0, 5]
"}" [0, 9] - [0, 10]
string_end [0, 10] - [0, 11]
```
and in particular no syntax error.
To fix this, we want to ensure that the `:` is lexed on its own, and the
`token(prec(1, ...))` construction can be used to do exactly this.
Finally, you may wonder why `=` is special here. I think what's going on
is that the lexer knows that `:=` is a token on its own (because it's
used in the walrus operator), and so it greedily consumes the following
`=` with this in mind.
Uses the same trick as for `ExtractedArgumentNode`, wherein we postpone
the global restriction on the charpred to instead be in the `argumentOf`
predicate (which is global anyway).
In addition to this, we also converted `CapturedVariablesArgumentNode`
into a proper synthetic node, and added an explicit post-update node for
it. These nodes just act as wrappers for the function part of call
nodes. Thus, to make them work with the variable capture machinery, we
simply map them to the closure node for the corresponding control-flow
or post-update node.
