The second interface in an IDL block causes the required-dict check to misfire on derived dicts

[tabatkins]

Yes, the title is weirdly specific, because the error is.

Take the following IDL snippet:

interface NeededForSomeReason {
};

interface Foo {
  undefined usesBase(BaseDict options);
  undefined usesDerived(DerivedDict options);
};

dictionary BaseDict {
  required DOMString req;
};

dictionary DerivedDict : BaseDict {
  DOMString opt;
};

This should be valid - both BaseDict and DerivedDict contain required members, so their use as method arguments without a default is valid. However, widlparser reports that the usesDerived() method's argument needs to be optional due to lacking required members.

The weird thing is this only happens if the interface triggering the error is the second in the block. If you remove the first interface, or swap the order of the two interfaces, there's no error.

(Reported in speced/bikeshed#3023 originally.)

[tabatkins]

Ah, to trigger it you specifically already need the symbol table, of course - otherwise it skips those checks. Here's a script which reproduces it:

from widlparser import Parser

class UI(object):
    def warn(self, s):
        print(f"\033[{0};{31}m{s}\033[0m")

    def note(self, s):
        print(f"\033[{0};{33}m{s}\033[0m")

class UISilent():
    def warn(self, s):
        pass
    def note(self, s):
        pass

idl = """interface NeededForSomeReason {
};

interface Foo {
    undefined usesBase(BaseDict options);
    undefined usesDerived(DerivedDict options);
};

dictionary BaseDict {
    required DOMString req;
};

dictionary DerivedDict : BaseDict {
    DOMString opt;
};"""
print("\n".join(f"{i:3d}: {line}" for i,line in enumerate(idl.split("\n"), 1)))

symbolParser = Parser(idl, ui=UISilent())
parser = Parser(idl, ui=UI(), symbol_table=symbolParser.symbol_table)

[tabatkins]

Still not sure why the error doesn't pop when you only have a single interface, tho. I guess i could poke around more to figure that out, make sure we're not messing something up somewhere.

[plinss]

Ok, so two bugs (both fixed).

First, the Dictionary class wasn't checking base Dictionaries for required props.
Second, there was a bug in symbol table registration where the first construct wasn't getting registered (that's why you needed the first dummy interface to trigger the bug).

Also FYI, the reason why you needed to parse twice and then use the symbol table from the first parser is because the Dictionaries are defined after where they're used. If you defined the Dictionaries first, you could've repro'd with one pass.