plugin: cannot load a plugin from a test where the plugin includes the tested package

[crawshaw]

On #17832 @wendigo notes that a go test for package p cannot load a plugin that imports package p without an error message about incorrect versions. This example is provided:

https://github.com/wendigo/go-plugin-33161

This is caused by the go tool rebuilding a package to include the test files, making the package in the test program incompatible with the equivalent package in the plugin.

I don't think this necessarily needs to work, it is entirely possible to do the plugin work from an external test from a package p_test. But maybe we could use a more helpful error message.

Any suggestions?

cc @ianlancetaylor

[wendigo]

plugin.so built with particular version of go cannot be loaded in any test package built with the same go version. From my perspective it basically limits possible usage of plugins as I cannot load and use plugins in tests and cannot test plugin itself in a test.

[crawshaw]

It cannot be loaded into a test that is inside a package included in the plugin. Try changing your test to a separate package, typically done by replacing the package declaration with package mypkg_test.

[wendigo]

Already done that in the attached test case - result is the same (it seems that test package name doesn't matter at all). Also plugin cannot be loaded from any package used by the test itself.

In my case I've tracked this error while developing https://github.com/wendigo/go-bind-plugin which generates API for wrapping symbols exported by a plugin. I've got package cli that loads, analyzes symbols using reflection and generates code for the wrapper. When cli is used in a cli_test package plugin.Open fails to load it with an error: plugin was built with a different version of package runtime. It works just fine when loading it outside of the go test (also without cherry-picked https://go-review.googlesource.com/#/c/33161/ it works just fine).

[wendigo]

Also I've noticed that for mismatched packages like runtime or os *pkghash.runtimehash is "" (empty string) when comparing it with non-empty pkghash.linktimehash in https://github.com/golang/go/blob/master/src/runtime/plugin.go#L45

[wendigo]

Any news @crawshaw? I noticed that sometimes plugin cannot be also loaded outside the test (plugin.Open: plugin was built with a different version of package runtime) and when I've examined md.pkghashes only mismatched packages in my case were os and runtime (both with empty runtimehash). I don't know how runtimehash is exactly calculated.

[wendigo]

Ping @crawshaw, @ianlancetaylor

[gopherbot]

CL https://golang.org/cl/33925 mentions this issue.