x/tools/refactor/rename: panic when renaming type embedded in another package

[isaiah]

This is similar to #8924

Following is the regression test:

diff --git a/refactor/rename/rename_test.go b/refactor/rename/rename_test.go
index 1d282a1..dedb399 100644
--- a/refactor/rename/rename_test.go
+++ b/refactor/rename/rename_test.go
@@ -721,6 +721,31 @@ type _ struct{ *foo.U }
                        },
                },

+               {
+                       ctxt: fakeContext(map[string][]string{
+                               "foo": {`package foo; type T int`},
+                               "main": {`package main
+
+import "foo"
+
+type V struct{ *foo.T }
+`},
+                       }),
+                       from: "(main.V).T", to: "U", // the "T" in *foo.T
+                       want: map[string]string{
+                               "/go/src/foo/0.go": `package foo
+
+type U int
+`,
+                               "/go/src/main/0.go": `package main
+
+import "foo"
+
+type V struct{ *foo.U }
+`,
+                       },
+               },
+

Stacktrace:

--- FAIL: TestRewrites-2 (0.01s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
        panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x62c78]

goroutine 248 [running]:
testing.func·006()
        /usr/local/Cellar/go/1.4.2/libexec/src/testing/testing.go:441 +0x181
golang.org/x/tools/refactor/rename.(*renamer).checkInPackageBlock(0x2085e0720, 0x2208594da0, 0x2085e8880)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/check.go:104 +0xe78
golang.org/x/tools/refactor/rename.(*renamer).check(0x2085e0720, 0x2208594da0, 0x2085e8880)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/check.go:39 +0x1cc
golang.org/x/tools/refactor/rename.(*renamer).checkStructField(0x2085e0720, 0x208610190)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/check.go:353 +0x871
golang.org/x/tools/refactor/rename.(*renamer).check(0x2085e0720, 0x2208595628, 0x208610190)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/check.go:41 +0x21a
golang.org/x/tools/refactor/rename.Main(0x20867f040, 0x0, 0x0, 0x378830, 0xa, 0x36f1f0, 0x1, 0x0, 0x0)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/rename.go:326 +0x122c
golang.org/x/tools/refactor/rename.TestRewrites(0x2085fa090)
        /Users/isaiah/codes/go/src/golang.org/x/tools/refactor/rename/rename_test.go:1014 +0x21fe
testing.tRunner(0x2085fa090, 0x50b8a8)
        /usr/local/Cellar/go/1.4.2/libexec/src/testing/testing.go:447 +0xbf
created by testing.RunTests
        /usr/local/Cellar/go/1.4.2/libexec/src/testing/testing.go:555 +0xa8b

It works if from is specified as offset, in which case rename can figure out which packages are affected, but if it's specified as main.V.T form, it failed to figure out the original package of the embedded field is also affected.

[davidrjenni]

I sent a fix.

[gopherbot]

CL https://golang.org/cl/13451 mentions this issue.