proposal: cmd/go: add .ʕ◔ϖ◔ʔ as an alternate spelling of .go in file names #59968
Description
The new (apparently closed-source) programming language Mojo uses files named .mojo, but it allows .🔥 as an alternate spelling of .mojo, as in hello.🔥.
Issue #45549 tracks handling of unicode in import paths, module paths, and file names. We have been proceeding cautiously due to the many subtle issues involved in cross-platform support, case-insensitive file systems, and so on: modules must work equally well on all supported systems.
Clearly Go is being left behind in the Unicode race. We must not let this stand. I propose that we throw caution to the wind and standardize on .ʕ◔ϖ◔ʔ as an alternate spelling of .go, as in hello.ʕ◔ϖ◔ʔ.
The change would be primarily in go/build: .ʕ◔ϖ◔ʔ files would be added to the GoFiles lists. There are probably a few places elsewhere in the toolchain that know the extension .go, such as go tool compile x.go writing out x.o, or VS Code registering .go as the file suffix it supports. These will no doubt be trivial to find.
In #57001, there was some concern about the semantics of Go build tags changing meaning in a subtle way. We could address that by only applying the new semantics in .ʕ◔ϖ◔ʔ files. Older toolchains already have code to ignore those.
There were similar concerns in the discussion #56010 about changing the semantics of for loops. The new .ʕ◔ϖ◔ʔ provides an answer: .go files get the old for loop semantics, while .ʕ◔ϖ◔ʔ get the new semantics.
For long-term migration, go fix can rename .go files to .ʕ◔ϖ◔ʔ
There are a few weeks left before the Go 1.21 freeze. That should be plenty of time for a careful, considered discussion of this proposal and then a complete implementation with no subtle problems. Let's go ʕ◔ϖ◔ʔ!