Replace |line|, |column|, and |offset| properties of tracing events with
the |location| property. It contains an object similar to the one
returned by the |location| function available in action code:
{
start: { offset: 23, line: 5, column: 6 },
end: { offset: 25, line: 5, column: 8 }
}
For the |rule.match| event, |start| refers to the position at the
beginning of the matched input and |end| refers to the position after
the end of the matched input.
For |rule.enter| and |rule.fail| events, both |start| and |end| refer to
the current position at the time the rule was entered.
Replace |line|, |column|, and |offset| properties of |SyntaxError| with
the |location| property. It contains an object similar to the one
returned by the |location| function available in action code:
{
start: { offset: 23, line: 5, column: 6 },
end: { offset: 25, line: 5, column: 8 }
}
For syntax errors produced in the middle of the input, |start| refers to
the first unparsed character and |end| refers to the character behind it
(meaning the span is 1 character). This corresponds to the portion of
the input in the |found| property.
For syntax errors produced the end of the input, both |start| and |end|
refer to a character past the end of the input (meaning the span is 0
characters).
For syntax errors produced by calling |expected| or |error| functions in
action code the location info is the same as the |location| function
would return.
Preform the following renames:
* |reportedPos| -> |savedPos| (abstract machine variable)
* |peg$reportedPos| -> |peg$savedPos| (variable in generated code)
* |REPORT_SAVED_POS| -> |LOAD_SAVED_POS| (instruction)
* |REPORT_CURR_POS| -> |UPDATE_SAVED_POS| (instruction)
The idea is that the name |reportedPos| is no longer accurate after the
|location| change (seea the previous commit) because now both
|reportedPos| and |currPos| are reported to user code. Renaming to
|savedPos| resolves this inaccuracy.
There is probably some better name for the concept than quite generic
|savedPos|, but it doesn't come to me.
Replace |line|, |column|, and |offset| functions with the |location|
function. It returns an object like this:
{
start: { offset: 23, line: 5, column: 6 },
end: { offset: 25, line: 5, column: 8 }
}
In actions, |start| refers to the position at the beginning of action's
expression and |end| refers to the position after the end of action's
expression. This allows one to easily add location info e.g. to AST
nodes created in actions.
In predicates, both |start| and |end| refer to the current position.
Fixes#246.
Beside the recursion detector, the visitor will also be used by infinite
loop detector.
Note the newly created |asts.matchesEmpty| function re-creates the
visitor each time it is called, which makes it slower than necessary.
This could have been worked around in various ways but I chose to defer
that optimization because real-world performance impact is small.
So far, left recursion detector assumed that left recursion occurs only
when the recursive rule is at the very left-hand side of rule's
expression:
start = start
This didn't catch cases like this:
start = "a"? start
In general, if a rule reference can be reached without consuming any
input, it can lead to left recursion. This commit fixes the detector to
consider that.
Fixes#190.
Parsers can now be generated with support for tracing using the --trace
CLI option or a boolean |trace| option to |PEG.buildParser|. This makes
them trace their progress, which can be useful for debugging. Parsers
generated with tracing support are called "tracing parsers".
When a tracing parser executes, by default it traces the rules it enters
and exits by writing messages to the console. For example, a parser
built from this grammar:
start = a / b
a = "a"
b = "b"
will write this to the console when parsing input "b":
1:1 rule.enter start
1:1 rule.enter a
1:1 rule.fail a
1:1 rule.enter b
1:2 rule.match b
1:2 rule.match start
You can customize tracing by passing a custom *tracer* to parser's
|parse| method using the |tracer| option:
parser.parse(input, { trace: tracer });
This will replace the built-in default tracer (which writes to the
console) by the tracer you supplied.
The tracer must be an object with a |trace| method. This method is
called each time a tracing event happens. It takes one argument which is
an object describing the tracing event.
Currently, three events are supported:
* rule.enter -- triggered when a rule is entered
* rule.match -- triggered when a rule matches successfully
* rule.fail -- triggered when a rule fails to match
These events are triggered in nested pairs -- for each rule.enter event
there is a matching rule.match or rule.fail event.
The event object passed as an argument to |trace| contains these
properties:
* type -- event type
* rule -- name of the rule the event is related to
* offset -- parse position at the time of the event
* line -- line at the time of the event
* column -- column at the time of the event
* result -- rule's match result (only for rule.match event)
The whole tracing API is somewhat experimental (which is why it isn't
documented properly yet) and I expect it will evolve over time as
experience is gained.
The default tracer is also somewhat bare-bones. I hope that PEG.js user
community will develop more sophisticated tracers over time and I'll be
able to integrate their best ideas into the default tracer.
Rename |generateCache{Header,Footer}| to |generateRule{Header,Footer}|
and change their responsibility to generate overall header/footer of a
rule function (when optimizing for speed) or the |peg$parseRule|
function (when optimizing for speed). This creates a natural place where
to generate tracing code (coming soon).
Action and predicate code can now see variables defined in expressions
"above" them.
Based on a pull request by Bryon Vandiver (@asterick):
https://github.com/pegjs/pegjs/pull/180Fixes#316.
The |visitor.build| function now supplies default visit functions for
visitors it builds. These functions don't do anything beside traversing
the tree and passing arguments around to child visit functions.
Having the default visit functions allowed to simplify several visitors.
David Majda