all: remove existing uses of io/ioutil package

[perillo]

The io/ioutil package is still used in go/build and net/http.

It is also widely used in the cmd module. I'm not sure if there was a reason why it was removed in std but not in cmd.

[perillo]

In Context.readDir there is a TODO note to "use os.ReadDir". However os.ReadDir returns fs.DirEntry so it is not possible to used it. Should the TODO note be removed?

[gopherbot]

Change https://golang.org/cl/310029 mentions this issue: net/http: replace ioutil.NopCloser with io.NopCloser

[tklauser]

It is also widely used in the cmd module. I'm not sure if there was a reason why it was removed in std but not in cmd.

Note that cmd/dist and (I think) some parts of cmd/compile and cmd/link need to remain buildable with Go 1.4 for bootstraping. Thus, these cannot use features newer than Go 1.4. Also see src/cmd/dist/README.

However, #44505 proposes to adopt Go 1.16 as the bootstrap toolchain for Go 1.18. That proposal was accepted, so we'll probably be able to replace io/ioutil there as well for Go 1.18.

[perillo]

@tklauser, right thanks. I always forgot that go is bootstrapped from go1.4. Fortunately I avoided touching the tests in the cmd module.

[mknyszek]

Since we can't really do this in large parts of the codebase for now, I suppose this can just be a tracking issue?

CC @rsc who deprecated io/ioutil (I'm honestly not sure who to CC on this, though).

[perillo]

@mknyszek: in the issue name I specified these changes to only apply to the std module, so it is ok. In future I will open another issue about the cmd module.

[rsc]

It's fine to leave this issue open but let's not do this work by hand. I intend to automate it as part of a more general "go fix" when the time comes.

[perillo]

Ok, thanks.

Currently, in the std module all imports of the io/ioutil package have been replaced, excluding go/build since Context.readDir calls ioutil.ReadDir (there is a TODO note that is probably wrong, since Context.readDir should call File.Readdir and not os.ReadDir, so the change should me done manually).

io/ioutil is also imported in the net/http package, in code generated from golang.org/x/net/http2, and in some vendored packages.

[gopherbot]

Change https://go.dev/cl/392074 mentions this issue: go/build: replace ioutil.ReadDir with os.ReadDir