proposal: Go 2: remove dot imports from the language

[ianlancetaylor]

This issue is broken out of #29036.

We should remove dot imports from the language (import . "path"). Quoting @rogpeppe:

The official guidelines suggest that a dot import should only be used "to let the file pretend to be part of package foo even though it is not". This is a stylistic choice and strictly unnecessary. The tests can still use package-qualified names with only minor inconvenience (the same inconvenience that any external user will see).

Other than that, I believe the most common use is to make the imported package feel "close to a DSL". This seems to be actively opposed to the aims of Go, as it makes the programs much harder to read.

[josharian]

While experimenting with #20104 just a few days ago, dot imports were incredibly useful—instead of having to plumb a bunch of context through complicated code generation scripts and carefully conditionally adjust a dozen format strings, I could just dot import ssa in the relocated files. Long term, I would choose to do the work to eliminate the dot import. But it was very helpful as scaffolding. And not just for experimentation: the dot import is a single line change for reviewers, whereas qualifying every package use would have made the diff unreadable (and unrecognizable to git as a file move).

To be clear (unlike type aliases), this kind of refactoring is strictly speaking possible without dot imports. It is just a lot more graceful with them.

[agnivade]

Other than that, I believe the most common use is to make the imported package feel "close to a DSL".

Yes, this is what Goa does; which is used by a lot of people. If we remove dot imports, the entire package will break.

I have no issues either way. Just wanted to point this out.

[beoran]

DSLs are an important use case for dot imports, I disagree that DSLs make programs harder to read. On the contrary, they make programs easier to read for specific types of program, such as the Goa examples shows, and more importantly also make a program easier to understand for non-programmer domain experts for whom the DSL has been designed. This is why I respectfully ask that this proposal be rejected.

[alanfo]

Although dot imports are a feature which should be used sparingly, I can't see the sense in banning them altogether.

There are definitely occasions when they are useful for testing and experimentation and there are some other reasonable uses as well - see for example golang/lint#179.

I often use them myself when importing the math package, so I can just write Cos instead of math.Cos. Admittedly this isn't the greatest of use cases but, for me at least, there is no risk of confusion as I would never use the names of math functions as public names in my own packages.

[deanveloper]

As per mentioned in #29036 (comment)

I've found dot-imports to be useful when writing tests. For instance:

package mypack_test

import . "github.com/deanveloper/mypack"

// ...

I wouldn't really mind the dot-import being removed. I was just adding my particular use case for them.

And to reiterate, I wouldn't mind dot-import being removed. It's just what I use them for.

[gotzmann]

Most of the popular programming language use some form of "dot import" without any hassles. Hows ftm.Printf is more clear then simple print or echo?

[bcmills]

Tests are a great argument for removing dot-imports. I've seen lots of tests that failed to catch extremely redundant identifiers, because the tests and examples didn't include the package name as everyone else would.

[bcmills]

At first glance math seems like a great argument for not removing them, but then consider functions like Jn, Y0, and Log: the former two are somewhat obscure, and the latter could easily collide with a similarly-named function in another package. I could see a reasonable argument for dot-importing trigonometric functions and rounding functions, but math overall seems like a bit of a stretch.

[deanveloper]

Hmm now that I think of it, I feel like I've heard a lot of this stuff before. I feel like this might be a duplicate, but I searched for proposals of removing dot imports but didn't find anything