It looks like I failed to properly quote certain characters in my initial bug report, so here it is formatted with Markdown, which should do the right thing with < and > symbols:

% cat cgo-panic.go
package p

// #include <stdlib.h>
import "C"

func f() {
    C.free(0, C.size_t(0))
}
% go build cgo-panic.go
# command-line-arguments
panic: overlapping edits: [58,80)->"func() { _cgo0 := /*line :7:9*/0; _cgoCheckPointer(_cgo0); _Cfunc_free(_cgo0); }()", [68,76)->" /*line :7:12*/_Ctype_size_t /*line :7:20*/"

goroutine 1 [running]:
cmd/internal/edit.(*Buffer).Bytes(0xc000086960, 0xc00000e148, 0x602de7, 0xe)
    /home/nickolai/tmp/go/src/cmd/internal/edit/edit.go:79 +0x598
main.(*Package).writeOutput(0xc0000c8000, 0xc0000ba140, 0x7fff391c7ff5, 0x11)
    /home/nickolai/tmp/go/src/cmd/cgo/out.go:597 +0x38d
main.main()
    /home/nickolai/tmp/go/src/cmd/cgo/main.go:356 +0xce3
%

It's kind of a terrible error message, but note that your program is invalid. C.free takes only a single argument.

Indeed, I just minimized this to a simple reproducing case. The original program was much larger, and the bad error message made it difficult to track down what was wrong (it was also some C function being called with the wrong number of arguments).

Change https://golang.org/cl/185797 mentions this issue: cmd/cgo: do not rewrite call if there are more args than parameters

@gopherbot Please open a backport issue for 1.12.

Backport issue(s) opened: #33081 (for 1.12).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

Backport issue(s) opened: #33082 (for 1.12).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

Change https://golang.org/cl/185997 mentions this issue: [release-branch.go1.12] cmd/cgo: do not rewrite call if there are more args than parameters