What steps will reproduce the problem?
1. make -C pkg/container/vector generate

What is the expected output?

pkg/container/vector/intvector.go and friends are regenerated correctly

What do you see instead?

lucky(~/go/src) % hg identify ; make -C pkg/container/vector generate
825dec400be8+ tip
< vector.go cat\
    | gofmt -r='Vector -> IntVector'\
    | gofmt -r='interface{} -> int'\
    > intvector.go\
    
panic: reflect: call of reflect.Value·Set on zero Value [recovered]
    panic: reflect: call of reflect.Value·Set on zero Value

runtime.panic+0xac /Users/dave/go/src/pkg/runtime/proc.c:1034
    runtime.panic(0xb08c0, 0xf8400a76c0)
main._func_004+0xcb /Users/dave/go/src/cmd/gofmt/rewrite.go:88
    main._func_004(0x6492, 0x21a8100, 0x21a8fb8, 0x21a8610)
----- stack segment boundary -----
runtime.panic+0xf3 /Users/dave/go/src/pkg/runtime/proc.c:1015
    runtime.panic(0xb08c0, 0xf8400a76c0)
reflect.Value·internal+0x8b /Users/dave/go/src/pkg/reflect/value.go:95
    reflect.Value·internal(0x0, 0x0, 0x150000af59, 0xa7b9, 0xf8400a6fc0, ...)
reflect.Value·Set+0x37 /Users/dave/go/src/pkg/reflect/value.go:715
    reflect.Value·Set(0xf8400495b0, 0xf8400a76a0, 0x0, 0x0, 0xf8400a3590, ...)
main.setValue+0x64 /Users/dave/go/src/cmd/gofmt/rewrite.go:91
    main.setValue(0xf8400495b0, 0xf8400a76a0, 0x0, 0x0, 0xf840049500, ...)
main.apply+0x16f /Users/dave/go/src/cmd/gofmt/rewrite.go:131
    main.apply(0xf84000c7d0, 0xf8400495b0, 0xf8400a76a0, 0x0, 0x8, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf8400a7640, 0xf84002b2d0, 0xb88d0, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x3440, ...)
main.apply+0x14f /Users/dave/go/src/cmd/gofmt/rewrite.go:131
    main.apply(0xf84000c7d0, 0xf8400495b0, 0xf8400a7620, 0x0, 0x18, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf8400a7500, 0xb5268, 0xc4ce0, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x34e8, ...)
----- stack segment boundary -----
main.apply+0x1f7 /Users/dave/go/src/cmd/gofmt/rewrite.go:122
    main.apply(0xf84000c7d0, 0xf840049620, 0xf8400a74e0, 0x0, 0x8, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf8400a7480, 0x0, 0x10, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf8400a70c0, 0x0, 0x18, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf84009e940, 0xf84002b2d0, 0xb9c80, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x3440, ...)
main.apply+0x14f /Users/dave/go/src/cmd/gofmt/rewrite.go:131
    main.apply(0xf84000c7d0, 0xf8400495b0, 0xf84009e920, 0xf84002b2d0, 0xb3430, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x34e8, ...)
main.apply+0x1f7 /Users/dave/go/src/cmd/gofmt/rewrite.go:122
    main.apply(0xf84000c7d0, 0xf840049620, 0xf84009e900, 0x0, 0x18, ...)
main._func_003+0xe7 /Users/dave/go/src/cmd/gofmt/rewrite.go:69
    main._func_003(0xf8400a1658, 0xf8400a1670, 0xf8400a3580, 0xf8400a3590, 0x357e, ...)
main.apply+0x28d /Users/dave/go/src/cmd/gofmt/rewrite.go:127
    main.apply(0xf84000c7d0, 0xf84001f700, 0xf84009e7e0, 0xf84009e7e0, 0xf8400a3580, ...)
main.rewriteFile+0x1ae /Users/dave/go/src/cmd/gofmt/rewrite.go:75
    main.rewriteFile(0xf840019700, 0xf8400017e0, 0xf840019700, 0xf8400017c0, 0xf840026de0, ...)
main._func_002+0x41 /Users/dave/go/src/cmd/gofmt/rewrite.go:31
    main._func_002(0xf8400143f0, 0xf840014340, 0x20c1, 0xf840026de0, 0xd8f3c, ...)
main.processFile+0x26c /Users/dave/go/src/cmd/gofmt/gofmt.go:112
    main.processFile(0xd8f3c, 0x6174733c00000010, 0xf84000fba0, 0xf84000f3f0, 0xf84000fb70, ...)
main.gofmtMain+0x3a5 /Users/dave/go/src/cmd/gofmt/gofmt.go:213
    main.gofmtMain()
main.main+0x1c /Users/dave/go/src/cmd/gofmt/gofmt.go:182
    main.main()
runtime.mainstart+0xf /Users/dave/go/src/pkg/runtime/amd64/asm.s:77
    runtime.mainstart()
runtime.goexit /Users/dave/go/src/pkg/runtime/proc.c:178
    runtime.goexit()
----- goroutine created by -----
_rt0_amd64+0x8e /Users/dave/go/src/pkg/runtime/amd64/asm.s:64
<standard input>:1:1: expected 'package', found 'EOF'
make: *** [generate] Error 2


Which compiler are you using (5g, 6g, 8g, gccgo)?

6g (also tried 8g)

Which operating system are you using?

lucky(~) % uname -v
Darwin Kernel Version 10.7.0: Sat Jan 29 15:17:16 PST 2011;
root:xnu-1504.9.37~1/RELEASE_I386

Which revision are you using?  (hg identify)

lucky(~/go/src) % hg identify
825dec400be8+ tip

Please provide any additional information below.

This occurred after http://golang.org/cl/4387044 was committed