[SR-11677] Offer a better diagnostic when && is used in trailing where clause declaration

[CodaFi]

Previous ID	SR-11677
Radar	rdar://38225184
Original Reporter	@CodaFi
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, Parser, StarterBug
Assignee	ninjiacoder (JIRA)
Priority	Medium

md5: 50a519e5af58b06b95d65605733d7cf0

Issue Description:

We currently emit a pile of garbage diagnostics about this declaration. We should instead offer a concise diagnostic that replaces the && with a comma.

extension Collection where Element == Int && Index == Int {
  
}

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

Hi, I'm a starter and willing to fix this. But I'm not sure where to start, can you give me some advice?

[CodaFi]

ninjiacoder (JIRA User) There's a bit at the bottom of Parser::parseGenericWhereClause that tries to check if there's a trailing comma. The easiest thing to do would be to check for the presence of && with

Tok.isBinaryOperator() && Tok.getText() == "&&";

Then emit a diagnostic and keep munging text. Let me know if you need any more pointers. When you begin to work on this, be sure to assign yourself to this SR!

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

@CodaFi Thank you for your advice. I've tried something today. I use `swift/utils/build-script -x` and after couple of hours generated `Swift.xcodeproj`.

If I edit the compiler source code for example `ParseGeneric.cpp`, how can I test Swift built by myself? Just need to rebuild the Xcode project with `swift` scheme and test with bin/swift?

By the way, I've read the code of `Parser::parseGenericWhereClause`, every if condition has code like `BodyContext->...` & `Status.setIsParseError()`. If I add a check for `&&`, do I need to care about this `BodyContext` & `Status`?

[CodaFi]

   If I edit the compiler source code for example `ParseGeneric.cpp`, how can I test Swift built by myself? 

You can use the scheme selector or the scheme editor to select the `swift` target. From there, any compiler arguments you need to supply, you can put into the `Arguments Passed on Launch` field and just run the compiler like a normal command line tool. An example of arguments you would use would be something like

-frontend -parse /Path/To/My/Test/File.swift

Which will construct a single frontend invocation that will run off and just parse the file and emit whatever diagnostics. To write a test, you need to attach the -verify flag. You can see an example of doing this in the Parse tests directory.

By the way, I've read the code of `Parser::parseGenericWhereClause`...

You shouldn't need to care about these things. They're just part of the way we handle control in the recursive descent parser.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

Thanks. I've added the check of `&&` to the bottom of `Parser::parseGenericWhereClause`. It works to emit a diagnostic of replacing "&&" with ",", but other garbage diagnostics still emit. Do I need to find the way to remove them?

/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:43: error: use ',' for spliting conditions rather than '&&'
extension Collection where Element == Int && Index == Int {}
                                          ^~
                                          ,
/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:43: error: expected '{' in extension
extension Collection where Element == Int && Index == Int {}
                                          ^
/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:59: error: top-level statement cannot begin with a closure expression
extension Collection where Element == Int && Index == Int {}
                                                          ^
/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:28: error: use of undeclared type 'Element'
extension Collection where Element == Int && Index == Int {}
                           ^~~~~~~
/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:59: error: closure expression is unused
extension Collection where Element == Int && Index == Int {}
                                                          ^
/Users/ninjiacoder/Development/swift-source/swift/test/Constraints/rdar38225184.swift:1:59: note: did you mean to use a 'do' statement?
extension Collection where Element == Int && Index == Int {}
                                                          ^
                                                          do 

[CodaFi]

Make sure you consume the token and continue parsing as though it were a comma.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

Oh I see. I just add the following code in the check:

consumeToken();
HasNextReq = true;

Then the garbage diagnostics disappear. It seems that it's fixed. l've made a [PR](#28033 please review it when you are available.

[swift-ci]

Comment by Ziyuan Zhao (JIRA)

The PR has been merged