gofmt: panic: runtime error: invalid memory address or nil pointer dereference

[gopherbot]

by tianyicui:

Before filing a bug, please check whether it has been fixed since
the latest release: run "hg pull -u" and retry what you did to
reproduce the problem.  Thanks.

What steps will reproduce the problem?
1. $ gofmt -r="α.Data() -> *α" main.go
(the related file main.go is attached)

What is the expected output?

I want to change things from "range self.pkgs.Data()" to "range
*self.pkgs" (self.pkgs is vector.StringVector). I'm not sure if I fully understand
the usage of -r flag of gofmt, but at least it should not end with a panic.

What do you see instead?

panic: runtime error: invalid memory address or nil pointer dereference

panic PC=0x3344f0
runtime.panic+0xb2 /Users/tianyi/OSS/go/src/pkg/runtime/proc.c:1015
    runtime.panic(0x0, 0x3226e8)
panicstring+0x69 /Users/tianyi/OSS/go/src/pkg/runtime/runtime.c:83
    panicstring(0x8ee70, 0x344a60)
sigpanic+0x148 /Users/tianyi/OSS/go/src/pkg/runtime/darwin/thread.c:460
    sigpanic()
reflect.*PtrValue·PointTo+0x27 /Users/tianyi/OSS/go/src/pkg/reflect/value.go:1062
    reflect.*PtrValue·PointTo(0x0, 0x4fa09, 0x351be0, 0xb7e01)
main.subst+0x338 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:227
    main.subst(0x351c00, 0x0, 0x0, 0x0, 0x0, ...)
main.subst+0x5e9 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:221
    main.subst(0x0, 0x346cc0, 0x351be0, 0x0, 0x0, ...)
main.subst+0x31c /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:227
    main.subst(0x0, 0x346d20, 0x3519c0, 0x0, 0x0, ...)
main.subst+0x446 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:232
    main.subst(0x0, 0x346cc0, 0x351980, 0x0, 0x0, ...)
main.subst+0x5e9 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:221
    main.subst(0x0, 0x346de0, 0x351940, 0x0, 0x0, ...)
main.subst+0x31c /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:227
    main.subst(0x0, 0x346d20, 0x3518c0, 0x0, 0x0, ...)
main.subst+0x178 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:200
    main.subst(0x0, 0x346cc0, 0x351600, 0x0, 0x0, ...)
main.subst+0x446 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:232
    main.subst(0x312d20, 0x346cc0, 0x351880, 0x346d20, 0x351760, ...)
main.subst+0x5e9 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:221
    main.subst(0x312d20, 0x346de0, 0x351840, 0x346d20, 0x351760, ...)
main.subst+0x31c /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:227
    main.subst(0x312d20, 0x346d20, 0x3517a0, 0x346d20, 0x351760, ...)
main._func_003+0x20d /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:61
    main._func_003(0x312d20, 0x346cc0, 0x315c60, 0x346d20, 0x351760, ...)
main.apply+0x10b /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:98
    main.apply(0x346cc0, 0x338ce0, 0x338ce0, 0x338cc0, 0x338c01, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346de0, 0x338cc0, 0x0, 0x89bb8, ...)
main.apply+0x1f4 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:94
    main.apply(0x346de0, 0x338cc0, 0x346de0, 0x338cc0, 0x1, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346cc0, 0x3388a0, 0x353208, 0x1, ...)
main.apply+0x10b /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:98
    main.apply(0x346cc0, 0x3388a0, 0x3388a0, 0x338880, 0x338801, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346de0, 0x338880, 0xb9240, 0x34d700, ...)
main.apply+0x2cf /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:89
    main.apply(0x346de0, 0x338880, 0x346de0, 0x338880, 0x338201, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346d80, 0x338280, 0x0, 0x77090, ...)
main.apply+0x1f4 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:94
    main.apply(0x346d80, 0x338280, 0x346d80, 0x338280, 0x338101, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346cc0, 0x3381a0, 0x0, 0x6ef38, ...)
main.apply+0x1f4 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:94
    main.apply(0x346cc0, 0x3381a0, 0x346cc0, 0x3381a0, 0x1, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346cc0, 0x33f260, 0x349a80, 0x1, ...)
main.apply+0x10b /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:98
    main.apply(0x346cc0, 0x33f260, 0x33f260, 0x33f240, 0x33f201, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346de0, 0x33f240, 0xb5240, 0x34d700, ...)
main.apply+0x2cf /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:89
    main.apply(0x346de0, 0x33f240, 0x346de0, 0x33f240, 0x350001, ...)
main._func_003+0xea /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:59
    main._func_003(0x34c4b0, 0x346d80, 0x350080, 0x0, 0x72278, ...)
main.apply+0x1f4 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:94
    main.apply(0x346d80, 0x350080, 0x346d80, 0x350080, 0x303d01, ...)
main.rewriteFile+0x1a5 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:65
    main.rewriteFile(0x34c4b0, 0x346cc0, 0x315c80, 0x315c80, 0x34e130, ...)
main._func_002+0x41 /Users/tianyi/OSS/go/src/cmd/gofmt/rewrite.go:31
    main._func_002(0x300540, 0x323ba0, 0x3004e0, 0x300510, 0x34c460, ...)
main.processFile+0x151 /Users/tianyi/OSS/go/src/cmd/gofmt/gofmt.go:101
    main.processFile(0x34c460, 0x7, 0xb2040, 0x332190)
main.processFileByName+0xa8 /Users/tianyi/OSS/go/src/cmd/gofmt/gofmt.go:137
    main.processFileByName(0x3004b0, 0x7, 0x0, 0x3004b0, 0x0, ...)
main.main+0x226 /Users/tianyi/OSS/go/src/cmd/gofmt/gofmt.go:201
    main.main()
mainstart+0xf /Users/tianyi/OSS/go/src/pkg/runtime/amd64/asm.s:78
    mainstart()
goexit /Users/tianyi/OSS/go/src/pkg/runtime/proc.c:145
    goexit()

What is your $GOOS?  $GOARCH?

GOOS=darwin
GOARCH=amd64

Which revision are you using?  (hg identify)

843a555976df


Please provide any additional information below.

Attachments:

1. main.go (5072 bytes)

[adg]

Comment 1:

It works for me at f78fafa04768+ tip.
Can you hg sync, run all.bash, and try again?

Status changed to WaitingForReply.

[gopherbot]

Comment 2 by tianyicui:

I hg-pulled "f78fafa04768+ tip", run all.bash, and got exactly the same output. What can
I do to help?

[griesemer]

Comment 3:

Owner changed to [email protected].

Status changed to Accepted.

[griesemer]

Comment 4:

The following program reproduces the crash:
package P
var _ = x.Data()

[griesemer]

Comment 5:

Several issues:
./gofmt -r="x -> x" test.go
panic: interface conversion: *ast.CommentGroup is not ast.Node: missing method Pos
package P
var _ = x
./gofmt -r="-x -> x" test.go
panic: runtime error: invalid memory address or nil pointer dereference
package P
var _ = -x

[griesemer]

Comment 6:

This issue was closed by revision a48b35e.

Status changed to Fixed.