cmd/cgo: CoreFoundation go-keychain compile failure on tip

[kevinburke]

Please answer these questions before submitting your issue. Thanks!

What did you do?

Check out tip of github.com/keybase/go-keychain (commit keybase/go-keychain@70b98e9) and run go build github.com/keybase/go-keychain

What did you expect to see?

I expected the program to compile.

What did you see instead?

$ go build .
# github.com/keybase/go-keychain
./corefoundation_1.10.go:55: cannot use nil as type _Ctype_CFAllocatorRef in argument to _Cfunc_CFDataCreate
./corefoundation_1.10.go:81: cannot use nil as type _Ctype_CFAllocatorRef in argument to func literal
./corefoundation_1.10.go:118: cannot use nil as type _Ctype_CFAllocatorRef in argument to _Cfunc_CFStringCreateWithBytes
./corefoundation_1.10.go:153: cannot use nil as type _Ctype_CFAllocatorRef in argument to func literal

Does this issue reproduce with the latest release (go1.10.3)?

No. I can reproduce it using tip though, which suggests that this code will break in the upcoming Go 1.11 release.

A git bisect revealed that commit 94076fe is the first commit to break; versions of Go compiled with commits earlier than this commit successfully compile the go-keychain library, newer ones don't.

System details

go version devel +94076feef5 Mon Jul 9 22:19:21 2018 +0000 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/kevin.burke/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/kevin.burke"
GOPROXY=""
GORACE=""
GOROOT="/Users/kevin.burke/go"
GOTMPDIR=""
GOTOOLDIR="/Users/kevin.burke/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/bs/n3zm0wvn7j14n9gm_ybk4klsg6mgyh/T/go-build618247201=/tmp/go-build -gno-record-gcc-switches -fno-common"
VGOMODROOT=""
GOROOT/bin/go version: go version devel +94076feef5 Mon Jul 9 22:19:21 2018 +0000 darwin/amd64
GOROOT/bin/go tool compile -V: compile version devel +94076feef5 Mon Jul 9 22:19:21 2018 +0000
uname -v: Darwin Kernel Version 17.7.0: Thu Jun 21 22:53:14 PDT 2018; root:xnu-4570.71.2~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.13.6
BuildVersion:	17G65
lldb --version: lldb-902.0.79.7
  Swift-4.1

[kevinburke]

I added the release blocker tag since the code in question works fine on Go 1.10 but breaks on Go 1.11. If the problem is determined to be in the go-keychain code, please feel free to remove the tag!

[odeke-em]

/cc @randall77 @ianlancetaylor

[randall77]

This is expected. We've expanded the cases where we change the CF*Ref types from real pointers to uintptrs. Places where they weren't being converted caused mismatches between source files in the same package. See issue #24161.
You'll need to change nil to 0 in a few places.
Sorry about that. Looks like you'll need a corefoundation_1.11.go :(

[ianlancetaylor]

If there are more cases in Go 1.10, then we should say something in the 1.11 release notes. I don't see anything there now.

[kevinburke]

If there are more cases in Go 1.10, then we should say something in the 1.11 release notes. I don't see anything there now.

This is the only library I've seen with a compatibility issue, though maybe we could do a fancy Github code search for, say, CFDataCreate(nil to see how many libraries have this problem.

[kevinburke]

There are a fair number of results here and there are 3 other function calls in the linked file that have compatibility issues so maybe I'll submit some patches against these projects. To be honest I don't really understand the underlying problem that well - even after reading through the linked issue - so I might just write "this needs to change for Go 1.11 and changing nil to 0 will make your code compile again."

https://github.com/search?p=2&q=language%3Ago+CFDataCreate%28nil&type=Code

[akalin-keybase]

An alternate fix I implemented in keybase/go-keychain#31 is to use the typed constant kCFAllocatorDefault, which works with both go 1.10 and 1.11. That saves having to have 1.11-specific files.

This takes care of the common case in CoreFoundation where either NULL or a typed constant can be passed in as an argument. I suspect a lot of the other cases can be handled similarly. At worst, one might need to add a typed constant in the C preamble.

[gopherbot]

Change https://golang.org/cl/127975 mentions this issue: doc: describe cgo ptr->uintptr changes for 1.11.