[AST] explicit PrintOptions default constructor

[omochi]

This PR add default constructor of PrintOptions explicitly.
This is already implemented by c++ compiler implicitly.
But, it can not be called from lldb session.

(lldb) p f->getLoweredFunctionType()->getString(PrintOptions())
error: call to implicitly-deleted default constructor of 'swift::PrintOptions'
default constructor of 'PrintOptions' is implicitly deleted because field 'BracketOptions' has no default constructor

If I add this explicitly, it become available.

(lldb) p f->getLoweredFunctionType()->getString(PrintOptions())
(std::__1::string) $1 = "@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32"

This is very useful for reading and studying swift compiler source code with debugger.

supplement

If I add default constructor of BracketOptions to follow error message,
It still can not be called because of another error.

(lldb) p PrintOptions()
error: Couldn't lookup symbols:
  __ZNSt3__18functionIFNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEEPKN5swift9ValueDeclEEEC1Ev
  __ZNSt3__18functionIFbPKN5swift13ExtensionDeclEEEC1Ev
  __ZNSt3__16vectorIN5swift11AnyAttrKindENS_9allocatorIS2_EEEC1Ev
  __ZNSt3__110shared_ptrIN5swift18ShouldPrintCheckerEEC1Ev

lldb seems can not call templated symbol which has not been instantiated.

[jrose-apple]

This looks like an LLDB bug. There should be no circumstances where Clang can synthesize a default constructor but LLDB can't (other than the template instantiation thing you mentioned).

We generally use the dump() methods for this purpose, and make sure one of those can always be called from the debugger. Is that not sufficient for what you're doing?

[dcci]

cc @fredriss / @shafik

[fredriss]

It's a know issue with current debuggers (not only LLDB). Templates are not described in the debug information, only template instantiations, thus the debugger doesn't know about anything that hasn't been instantiated. Even if it's been instantiated but all the instances have been inlined, the debugger won't be able to access it.

[jrose-apple]

Sorry, we were asking about the default constructor part, not the template part.

[fredriss]

Oh, I see. Sounds more like a Clang bug than and LLDB one. I suppose what happens is that Clang doesn't emit the debug info describing implicitly generated constructors?

[jrose-apple]

If I'm understanding correctly, this is a case where the constructor wasn't generated, but it should be possible for LLDB to generate it.

[fredriss]

Currently LLDB never generates methods/*tors, it just calls them and they have to be present in the generated image. We are playing with the idea of generating what's not there, but it is quite tricky.

If the error message about implicitly deleting the constructor is correct, lldb would not have been able to generate it anyway. If the error message is incorrect, then it's worth an LLDB bug report.

[omochi]

Thanks to response.

I know about dump().
But they emit outputs to stdout of process.
I often debug swiftc by xcode with Wait for executable to be launched.
(Because terminal is easier than xcode's scheme dialog)
So there are 2 window which are terminal with $ swiftc and xcode.
So I use (lldb) expr type->dump() in xcode, then I need to switch terminal to read result.
Its inconvenience.
If I get result by value in lldb session, its useful.

Anyway I understand about lldb behavior and thanks to tell details.

I will investigate about using dump(raw_osteam) overload to solve my case.

[omochi]

@jrose-apple Hello.
I am working about this issue now.
https://bugs.swift.org/browse/SR-8499

Type::getString(PrintOptions) is important about this.

If Type::dump() prints escaping,
Type::getString() does not print @escaping sometime.

Former see resolved type information.
Latter see ParameterTypeFlags in AnyFunctionType::Param.
They are different sometime.

I am diving into ConstraintSystem, so its very complex.
I want to see temporary status about Type::getString.

It is a problem that default constructor value of PrintOptions can not be created from lldb.
I can use other value such like PrintOptions::printVerbose(),
But It may cause another behavior.

[jrose-apple]

All right. Please add a comment that says "This is explicit to guarantee that it can be called from LLDB", or something similar.

[omochi]

Thanks! I will do later.

[omochi]

@jrose-apple Please review it.

[dcci]

I assume you tried using PrintOptions() = default and it doesn't work? Otherwise, lgtm.

[dcci]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 42ed1fdb9cded4882732d87f5e16d6ed7924925f

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 42ed1fdb9cded4882732d87f5e16d6ed7924925f