[Concurrency] suppress global variable static checking for @TaskLocal property wrapper declarations

[sophiapoirier]

Explanation: This change resolves a bug in the SE-0412 implementation that makes it impossible to use the @TaskLocal property wrapper with strict concurrency enabled. This is due to the fact that @TaskLocal property wrappers are required to be static, and their storage is always declared var, and so they appear to the type checker as mutable global state, however the implementation of @TaskLocal ensures isolation to a single task, thereby obviating data race concerns. This change suppresses strict concurrency diagnostics for @TaskLocal declarations. Note that this is a temporary solution for 5.10 to unblock developers from experimenting with strict concurrency. The more complete solution will be to move to a TaskLocal macro as described in rdar://121054518 and will be developed on main branch.

Scope: minor change to skip past @TaskLocal declarations during type checking under strict concurrency and the changes are guarded behind an upcoming feature flag

Issue: rdar://120907014

Risk: low risk given that the change is in functionality that is guarded behind -strict-concurrency=complete feature flag and the fact that @TaskLocal property wrapper instances do not have concurrency concerns.

Testing: lit tests included

Reviewer: @ktoso @hborla

[ktoso]

This should preferably check for the exact decl rather than the name -- I'll whip up a snippet for it

[ktoso]

Like so:

          if (auto *classDecl =
                  var->getInterfaceType()->getClassOrBoundGenericClass()) {
            auto &ctx = var->getASTContext();
            auto taskLocalDecl = ctx.getTaskLocalDecl();
            if (classDecl == taskLocalDecl) {
              return isolation;
            }
          }

That'll avoid triggering for user-defined types of the same name

[sophiapoirier]

Thanks very much @ktoso I suspected there was a more robust way to check, and I had seen the TaskLocal info in KnownSDKTypes.def but was unsure how it functioned or might help.

[ktoso]

Happy to help :)

Usually if we have a type we know about and want to speak about it we put those into Known... and then can on ASTContext get them to compare etc. 👍

[ktoso]

Failures are the removed warning:

26540 /home/build-user/swift/test/Concurrency/task_local.swift:11:33: error: expected warning not produced
26541   static var number: Int = 0 // expected-complete-warning {{static property 'number' is not concurrency-safe because it is non-isolated global shared mutable state; this is an error in Swift 6}}
26542                             ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26543 ····························
26544 /home/build-user/swift/test/Concurrency/task_local.swift:12:6: error: expected note not produced
26545   // expected-complete-note@-1 {{isolate 'number' to a global actor, or convert it to a 'let' constant and conform it to 'Sendable'}}
26546 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26547 /home/build-user/swift/test/Concurrency/task_local.swift:15:31: error: expected warning not produced
26548   static var someNil: Int? // expected-complete-warning {{static property 'someNil' is not concurrency-safe because it is non-isolated global shared mutable state; this is an error in Swift 6}}
26549                           ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26550 ··························
26551 /home/build-user/swift/test/Concurrency/task_local.swift:16:6: error: expected note not produced
26552   // expected-complete-note@-1 {{isolate 'someNil' to a global actor, or convert it to a 'let' constant and conform it to 'Sendable'}}
26553 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26554 /home/build-user/swift/test/Concurrency/task_local.swift:21:6: error: expected warning not produced
26555   // expected-complete-warning@-2 {{static property 'noValue' is not concurrency-safe because it is non-isolated global shared mutable state; this is an error in Swift 6}}
26556 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26557 /home/build-user/swift/test/Concurrency/task_local.swift:22:6: error: expected note not produced
26558   // expected-complete-note@-3 {{isolate 'noValue' to a global actor, or convert it to a 'let' constant and conform it to 'Sendable'}}
26559 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
26560

[hborla]

Please fill out the 5.10 cherry pick PR description template

[sophiapoirier]

@swift-ci please test