Express noncopyability through the suppression of `Copyable` #64699

kavon · 2023-03-28T23:18:05Z

See https://forums.swift.org/t/second-review-se-0390-noncopyable-structs-and-enums/63866

This implements ~Copyable constraints, which means "suppress the implicit conformance to Copyable for this type"

That's not the final accepted syntax; writing without Copyable appears to have the most support on the forums. A follow-up PR will change this syntax once the dust has settled from the review.

companion PR: swiftlang/swift-syntax#1588

resolves rdar://106775103

kavon · 2023-04-05T04:24:00Z

@swift-ci please smoke test

kavon · 2023-04-05T18:49:43Z

@swift-ci please smoke test

kavon · 2023-04-18T23:20:37Z

@swift-ci smoke test

kavon · 2023-04-19T18:50:32Z

@swift-ci smoke test macOS

kavon · 2023-04-19T19:50:56Z

@swift-ci please clean smoke test

kavon · 2023-04-20T04:20:07Z

@swift-ci please test

kavon · 2023-04-26T01:21:46Z

swiftlang/swift-syntax#1588
@swift-ci please test

kavon · 2023-04-26T04:05:02Z

swiftlang/swift-syntax#1588
@swift-ci please test

kavon · 2023-04-26T17:18:07Z

Just some minor missed test updates. I think this is ready for review.

lib/AST/ASTPrinter.cpp

kavon · 2023-04-27T06:53:21Z

swiftlang/swift-syntax#1588
@swift-ci please test

Also has been referred to as "without Copyable" See SE-390 for details, or read the discussion here: https://forums.swift.org/t/second-review-se-0390-noncopyable-structs-and-enums/63866

many of these are mechanical changes

…ly types work with library evolution

Rather than try to omit explicit uses of `Copyable` in the output module for backwards compatability, we instead make it an error to use `Copyable` as a type when not suppressed. While it's straightforward to omit it for generic parameters, for uses of `Copyable` as an existential, we'd need to emit `Any` in its place. We'd also need to find and omit or modify explicit type constraints or same-type requirements involving Copyable. All of that sounded rather gross, and not really needed right now since any uses of `Copyable` explicitly is just not needed. update test with Copyable being banned generally

This will help prevent condfails when older compilers try to typecheck interfaces with `~Swift.Copyable` in them.

kavon · 2023-04-27T19:05:16Z

@swift-ci please test

kavon · 2023-04-27T23:37:27Z

swiftlang/swift-syntax#1588
@swift-ci please smoke test

kavon · 2023-04-28T00:56:10Z

@swift-ci please smoke test

kavon

mostly NFC feedback but also noticed some issues.

include/swift/AST/Decl.h

include/swift/AST/DiagnosticsParse.def

kavon · 2023-04-29T02:27:59Z

lib/AST/ASTPrinter.cpp

+  auto unprintable = [&options](Type subTy) {
+    if (auto aliasTy = dyn_cast<TypeAliasType>(subTy.getPointer()))
+      return !options.shouldPrint(aliasTy->getDecl());
+    if (auto NTD = subTy->getAnyNominal()) {
+      if (!options.shouldPrint(NTD))
+        return true;
+    }
+    return false;
+  };
+
+  // Collect types / suppressed entries written in the inheritance clause.
  for (auto entry: inherited) {
    if (auto ty = entry.getType()) {
-      bool foundUnprintable = ty.findIf([&](Type subTy) {
-        if (auto aliasTy = dyn_cast<TypeAliasType>(subTy.getPointer()))
-          return !options.shouldPrint(aliasTy->getDecl());
-        if (auto NTD = subTy->getAnyNominal()) {
-          if (!options.shouldPrint(NTD))
-            return true;
-        }
-        return false;
-      });
-      if (foundUnprintable)
+      if (ty.findIf(unprintable))


reverting this NFC hunk would be nice

kavon · 2023-04-29T02:30:31Z

lib/AST/Decl.cpp

+      if (suppressedParam)
+        return true;
+
+      // TODO: eventually once where clauses support suppression, this ought to


kavon · 2023-04-29T02:31:44Z

lib/AST/RequirementMachine/RequirementLowering.cpp

    Type inheritedType
      = evaluateOrDefault(ctx.evaluator,
                          InheritedTypeRequest{decl, index,
                          TypeResolutionStage::Structural},
                          Type());
    if (!inheritedType) continue;

+    // handle suppressed requirements
+    if (inheritedEntries[index].isSuppressed) {
+      // TODO: we should be adding a requirement for Copyable if not suppressed.


rephrase this as a future direction

kavon · 2023-04-29T03:01:25Z

lib/Sema/TypeCheckRequestFunctions.cpp

+    Evaluator &evaluator,
+    TypeOrExtensionDeclPointer decl,
+    unsigned index, TypeResolutionStage stage) const {
+  return resolveTypeLocWithin(decl, index, stage, getInheritedEntryAtIndex);


could revert this refactoring as it's not required anymore.

kavon · 2023-04-29T03:02:26Z

lib/Sema/TypeCheckType.cpp

+        case TypeReprKind::Suppressed:
+          // Can't have a suppressed type as a function param.
+          diagnose(specifierRepr->getLoc(), diag::suppression_illegal_here);


ensure test coverage of this; forget if i added it

kavon · 2023-04-29T03:07:23Z

lib/Sema/TypeCheckType.cpp

@@ -4314,6 +4345,39 @@ TypeResolver::resolveCompileTimeConstTypeRepr(CompileTimeConstTypeRepr *repr,
  return resolveType(repr->getBase(), options);
 }

+NeverNullType
+TypeResolver::resolveSuppressedTypeRepr(SuppressedTypeRepr *repr,


what happens if you tried

struct S: ~U {} struct U: ~S {}

kavon · 2023-04-29T03:09:54Z

lib/Serialization/Deserialization.cpp

+      // The first bit indicates "@unchecked", second bit indicates suppression.
+      bool isUnchecked = rawID & 0b01;
+      bool isSuppressed = rawID & 0b10;
+      TypeID typeID = rawID >> 2;


NOTE: this is why reading an old module would be impossible.

kavon · 2023-04-29T03:12:45Z

stdlib/public/core/CompilerProtocols.swift

+/// For older compilers interacting with newer stdlibs, define the unavailable
+/// `_Copyable` marker protocol that they expect to find.
+@available(*, unavailable)
+typealias _Copyable = Copyable


must be a public typealias! I also wonder if it being a typealias even works. to play it safe maybe just duplicate the old one right here:

/// This marker protocol represents types that support copying. /// This type is not yet available for use to express explicit /// constraints on generics in your programs. It is currently /// only used internally by the compiler. @available(*, unavailable) @_marker public protocol _Copyable {}

kavon · 2023-04-29T03:15:59Z

@swift-ci please test

kavon mentioned this pull request Mar 28, 2023

add parsing for ~ (the 'without' operator) swiftlang/swift-syntax#1461

Merged

kavon force-pushed the suppress-copyable branch 2 times, most recently from acf7b56 to 8c258a6 Compare April 4, 2023 05:14

kavon force-pushed the suppress-copyable branch from 718c2d7 to fc3194e Compare April 18, 2023 23:19

kavon force-pushed the suppress-copyable branch 2 times, most recently from 0a57160 to 2a63c25 Compare April 20, 2023 04:16

kavon force-pushed the suppress-copyable branch 2 times, most recently from 5a28271 to 00bfe00 Compare April 26, 2023 01:09

kavon added 3 commits April 25, 2023 18:12

add missing undef in metaprogramming

df231fd

add a notion of suppressible known protocols

8451e7f

rename _Copyable to Copyable and make it available

bfe2edc

kavon force-pushed the suppress-copyable branch 2 times, most recently from e0dbd4c to c006a38 Compare April 26, 2023 01:20

kavon marked this pull request as ready for review April 26, 2023 17:18

kavon requested review from ahoppen, bnbarham, rintaro, hborla, slavapestov, xedin and CodaFi as code owners April 26, 2023 17:18

kavon requested review from ktoso, artemcm, tshortli, zoecarver, hyp and egorzhdan as code owners April 26, 2023 17:18

kavon requested a review from gottesmm April 26, 2023 17:18

tshortli reviewed Apr 26, 2023

View reviewed changes

lib/AST/ASTPrinter.cpp Show resolved Hide resolved

kavon mentioned this pull request Apr 26, 2023

redo 'without' operator parsing so it's within parseType to match C++ parser swiftlang/swift-syntax#1588

Merged

kavon force-pushed the suppress-copyable branch from 47162b3 to 4dcd8ca Compare April 27, 2023 02:36

kavon added 9 commits April 27, 2023 11:33

implement ~Copyable to suppress implicit conformance to Copyable

50067a6

Also has been referred to as "without Copyable" See SE-390 for details, or read the discussion here: https://forums.swift.org/t/second-review-se-0390-noncopyable-structs-and-enums/63866

[tests] use ~Copyable instead of @_moveOnly

ba340c5

many of these are mechanical changes

[tests] improve a test to cover ~Copyable

1562daf

[tests] improve the parse-stdlib test

a86bb8c

[tests] add very basic test to ensure modules / interfaces for moveon…

c4c2af2

…ly types work with library evolution

[tests] remove outdated FIXME

f9f5e30

allow Copyable only in stdlib, with warning

fc6d526

add $SuppressedConformances feature flag

3e735ab

This will help prevent condfails when older compilers try to typecheck interfaces with `~Swift.Copyable` in them.

kavon force-pushed the suppress-copyable branch from 4dcd8ca to 3e735ab Compare April 27, 2023 19:01

clean-ups

58f1170

kavon force-pushed the suppress-copyable branch from 3f2f702 to 58f1170 Compare April 29, 2023 02:19

kavon commented Apr 29, 2023

View reviewed changes

kavon mentioned this pull request May 1, 2023

Build support for ~Copyable atop @_moveOnly #65556

Merged

kavon closed this Oct 19, 2023

Express noncopyability through the suppression of Copyable #64699

Express noncopyability through the suppression of Copyable #64699

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Express noncopyability through the suppression of `Copyable` #64699

Express noncopyability through the suppression of `Copyable` #64699

kavon commented Mar 28, 2023 •

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