Promote lack of existential `any` back to an error?

Using Swift
1

in Swift 6, lack of existential any was an error, if enableUpcomingFeature("ExistentialAny") was included in the Package.swift manifest.

in 6.1, this seems to have been downgraded to a warning. is there any setting that can promote this back to an error?

2

i think it might be possible to re-promote via the warning control flags from SE-0443. in a direct invocation to swiftc using both -enable-upcoming-feature ExistentialAny and -Werror ExistentialAny appears to cause the warnings to be promoted to errors in the 6.1 compiler. not sure exactly if/how to configure that for use in SPM though.

3

unfortunately, this does not seem to be compatible with SwiftPM

% swift build -Xswiftc -Werror -Xswiftc ExistentialAny
[1/1] Planning build
Building for debugging...
error: conflicting options '-Werror' and '-suppress-warnings'
4

Warning control settings for SPM are under way in SE-0480.

1 Like
5

i inherited a code base with (what i estimate to be) a low thousands number of occurrences of this problem. it takes several minutes to build the project from scratch, and unlike errors, incremental builds do not surface warnings. is there anything that can help me speed up this task?

6

are the targets under your control the ones specifying the -suppress-warnings flag? if so, removing that and setting the error promotion flags via the manifest rather than command line might be an option.

7

as far as i can tell, this is something that SwiftPM injects:

$ swift build -Xswiftc -Werror -Xswiftc ExistentialAny -v | grep suppress
/home/ubuntu/x86_64/6.1.2/usr/bin/swiftc  ... \
 -parseable-output -parse-as-library -swift-version 6 -g -Werror ExistentialAny -Xcc -fPIC -Xcc -g -suppress-warnings -user-module-version 0.29.0 -package-name javascriptkit -Xcc -fno-omit-frame-pointer
8

yes, i believe you're correct (see here), but it seems like it does that only for 'remote' packages. i'm not entirely sure what the semantics there are, but perhaps the package manifests for the 'local' packages could leverage the error promotion flags.