mockgen: handle more cases of "duplicate" imports

[stevendanna]

Description

This partially addresses two issues related to how the source-mode parser handles embedded interfaces from other packages. Each is addressed in their own commit, but I've submitted this as a single PR since it is modifying very similar code. The problems this addresses are:

Incorrect generation caused by packages with the same name

When an interface embeds other interfaces that happen to refer to packages with the same name, we would previously generate incorrect mocks. For example, given following code:

// source
import (
    "some.org/package/foo"
    "some.org/package/bar"
)

type Source interface {
    foo.Foo
    bar.Bar
}

// some.org/package/foo
package foo

import "some.org/package/foo/internal/bar"

type Foreign interface {
    bar.InternalBar
}

// some.org/package/bar

type Bar interface {
    TopLevelBarMethod() string
}

// some.org/package/foo/internal/bar

type Bar interface {
    InternalBarMethod() string
}

the resulting mock would have two generated implementations of TopLevelBarMethod() and no copies of InternalBarMethod(). This was because all interfaces were merged into a single map keyed by the package name.

We solve this by creating a tree of fileParser objects rather than merging all imports and interfaces into a single set of maps. This helps ensure that transitive imports from the source file's dependencies don't erroneously conflict with any top-level imports.

Fatal Error on duplicate imports

Previously, it was possible to get the following error:

2020/02/24 10:22:25 imported package collision: "log" imported twice

From a multi-file package that happens to import two packages named "log." While the package itself is valid, the parser can't currently handle this case because it merges all imports into a single map. Fully fixing this issue will likely require larger changes. Here, we cover what I think will be many of the common cases of hitting this error by deferring the error until the ambiguous package name is actually referenced. This is enough to handle the following common case which currently results in this error:

package service

import "google.golang.org/grpc"

type Test interface {
        grpc.ClientStream
}

Partially fixes #156
_

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests: I've added a new integration-style test in mockgen/internal/tests/import_embedded_interface/

Reviewer Notes

• The code flow looks good.
• Tests added.

Release Notes

- Improved handling of embedded interfaces in source-mode parser.

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[stevendanna]

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[codyoss]

Thank you for your contribution, this is awesome. I am going to get one more set of eyes on this as well.

[codyoss]

Do you think it would be possible to address this use case as well in this PR? Before your changes this would have manifested as: imported package collision: "rand" imported twice

type Foo interface {
	http.ResponseWriter
}

[stevendanna]

@codyoss That's a great test case, thanks! It caught a bug for which I've pushed a fix. I've added that example to the mockgen integration tests.

There is still a problem with interfaces from dot imports, but since this is also a limitation on master, I think I'd like to defer addressing it for now.

[stevendanna]

Heya, no rush here, just wondering if there is anything else y'all need from me on this one.

[cvgw]

LGTM! Thanks for the contribution

[CecileRobertMichon]

Hi there 👋Thanks for the fix! Are there any plans to include this in a release?

@codyoss @cvgw

[codyoss]

Yes, I plan on getting a release out sometime next week. Just need to do a little cleanup before then 😄

[ledmonster]

Could you please release this PR?

[CecileRobertMichon]

@codyoss I don't see this PR included in the latest release, any updates?

[codyoss]

Sorry, about sluggishness here. Once #478 has landed I plan to cut a formal release. In the meantime if this is a blocker for you can always pin to HEAD temporarily: go get github.com/golang/mock@HEAD

[CecileRobertMichon]

Thanks! That's what we've been doing but was just checking if we can get back to an official release soon.

[codyoss]

I will be sure to ping this thread when I have drafted a release.

[codyoss]

This too far too long, but here it is: https://github.com/golang/mock/releases/tag/v1.5.0