x/tools/cmd/gorename: panics when displaying diff

[ScottMansfield]

This is for the golang/tools repository, but can't open an issue there.

Running gorename with the diff display option panics when diff returns no data. Because err is not checked (because of the diff return codes) before display, the display part can panic when the diff output is nil.

My run on my local machine gave me a panic:

$ gorename -d -from '"github.com/netflix/rend/common".BAD_FLAGS' -to ErrorBadFlags
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x20 pc=0xa29b1]

goroutine 1 [running]:
golang.org/x/tools/refactor/rename.diff(0xc820898140, 0x46, 0xc823e76000, 0xe6b, 0xeb6, 0x0, 0x0)
    /Users/smansfield/gopkg/src/golang.org/x/tools/refactor/rename/rename.go:503 +0x3d1
golang.org/x/tools/refactor/rename.(*renamer).update(0xc823e41740, 0x0, 0x0)
    /Users/smansfield/gopkg/src/golang.org/x/tools/refactor/rename/rename.go:459 +0x10f7
golang.org/x/tools/refactor/rename.Main(0x48a700, 0x0, 0x0, 0x7fff5fbffa12, 0x2a, 0x7fff5fbffa41, 0xd, 0x0, 0x0)
    /Users/smansfield/gopkg/src/golang.org/x/tools/refactor/rename/rename.go:348 +0x1369
main.main()
    /Users/smansfield/gopkg/src/golang.org/x/tools/cmd/gorename/main.go:49 +0x337

return code: 2

I will be submitting a small patch to prevent this panic and provide some output.

[ScottMansfield]

After trying to patch locally, I noticed that stdout is actually nil. I may be missing something when running gorename, but I'm not sure what.

[ScottMansfield]

Adding logic to set stdout to os.Stdout fixed the issue. The test used inside knowledge of the files to set the stdout variable to os.Stdout when running tests. To not break the tests, I've not restructured the files but added some logic to the flag parsing to set stdout properly. I'm working on getting gerrit set up to submit a patch.

[ianlancetaylor]

CC @alandonovan

[ScottMansfield]

I have a change ready for review, but the CLA is taking a while to show up in gerrit. Just waiting on that before git codereview mail-ing

[ScottMansfield]

Gerrit is not picking up the CLA I had already signed before signing up with Gerrit. Trying again doens't work, since I already signed once. Any chance of an assist here?

[bradfitz]

@ScottMansfield, email me details (which email you're trying, whether it's your gmail, what Gerrit says, etc). My github username at golang.org.

[ScottMansfield]

Submitted CL: https://go-review.googlesource.com/#/c/18813/