🛑 DON'T MERGE [test] Fix source-stability test and revert #18793

[lorentey]

rdar://problem/43425867

[lorentey]

@swift-ci please test

[jrose-apple]

Wait, this seems backwards? Why would they switch like this?

[lorentey]

They didn't -- these became typealiases to Dictionary.Iterator and Set.Iterator, respectively, but they kept the same generic signatures.

@nkcsgexi Is this right?

[nkcsgexi]

The correct diags are actually like these:
-Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to
-Struct SetIterator has generic signature change from to <Key, Value>
+Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Key, Value>
+Struct SetIterator has generic signature change from to

[lorentey]

I copy & pasted the ones in this PR from my own test logs, with no edits -- is it possible the api-digester output is somehow nondeterministic?

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 15e368e

[lorentey]

12:44:31 -Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Element>
12:44:31 -Struct SetIterator has generic signature change from <Element where Element : Hashable> to <Key, Value>
12:44:31 +Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Key, Value>
12:44:31 +Struct SetIterator has generic signature change from <Element where Element : Hashable> to <Element>

Interesting -- in this build, it reverted to a less surprising (although still spurious) change.

[lorentey]

@swift-ci test

[nkcsgexi]

hmm, that'll be a bug of the tool. nondeterministic outputs will manifest as a flaky test. could we run the CI multiple times and see?

[lorentey]

We'll see a second run soon; the new CI build is almost done compiling.

[lorentey]

It looks like api-digester definitely has nondeterministic output -- I've seen four different variants in six local test runs:

+Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Element where Element : Hashable>
+Struct SetIterator has generic signature change from <Element where Element : Hashable> to <Key, Value>
---
+Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Element where Element : Hashable>
+Struct SetIterator has generic signature change from <Element where Element : Hashable>
---
+Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Element where Element : Hashable>
+Struct SetIterator has generic signature change from <Element where Element : Hashable> to <Key, Value>
---
+Struct DictionaryIterator has generic signature change from <Key, Value where Key : Hashable> to <Key, Value>
(note missing SetIterator)

[lorentey]

Yep, the test has passed in the current build, despite the earlier failure:

PASS: Swift(macosx-x86_64) :: api-digester/source-stability.swift (7913 of 11307)

[nkcsgexi]

Thanks, I'll investigate what's going on.

[nkcsgexi]

hmm, i cannot reproduce the nondeterministic output issue locally. We should run the swift-ci multiple times here to see if it reproduces.

[nkcsgexi]

oh, i can reproduce this issue with more runs. It seems SetIterator and DictionaryIterator have been changed from a type decl to a typealias decl, thus the tool is confused with mapping. I'll investigate the fix.

[lorentey]

See #18811 for the correct fix.