Issue 1:
What steps will reproduce the problem?

run tests

What do you see instead?

WARNING: DATA RACE
Read by goroutine 17:
go/token.(*FileSet).file()
/build/go.tip/go/src/pkg/go/token/position.go:371 +0x38
go/token.(*FileSet).Position()
/build/go.tip/go/src/pkg/go/token/position.go:403 +0x70
go/printer.(*printer).posFor()
/build/go.tip/go/src/pkg/go/printer/printer.go:142 +0x58
go/printer.(*printer).print()
/build/go.tip/go/src/pkg/go/printer/printer.go:894 +0xa70
go/printer.(*printer).expr1()
/build/go.tip/go/src/pkg/go/printer/nodes.go:805 +0x1564
go/printer.(*printer).expr0()
/build/go.tip/go/src/pkg/go/printer/nodes.go:878 +0x59
go/printer.(*printer).exprList()
/build/go.tip/go/src/pkg/go/printer/nodes.go:243 +0x10b7
go/printer.(*printer).stmt()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1083 +0x2593
go/printer.(*printer).stmtList()
/build/go.tip/go/src/pkg/go/printer/nodes.go:908 +0x29c
go/printer.(*printer).block()
/build/go.tip/go/src/pkg/go/printer/nodes.go:921 +0x132
go/printer.(*printer).adjBlock()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1483 +0x692
go/printer.(*printer).funcDecl()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1507 +0x38d
go/printer.(*printer).decl()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1517 +0xb2
go/printer.(*printer).declList()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1558 +0x1c5
go/printer.(*printer).file()
/build/go.tip/go/src/pkg/go/printer/nodes.go:1566 +0x1ef
go/printer.(*printer).printNode()
/build/go.tip/go/src/pkg/go/printer/printer.go:1057 +0x8f8
go/printer.(*Config).fprint()
/build/go.tip/go/src/pkg/go/printer/printer.go:1196 +0xbe
go/printer.(*Config).Fprint()
/build/go.tip/go/src/pkg/go/printer/printer.go:1254 +0x89
go/printer.format()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:62 +0x3fc
go/printer.runcheck()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:154 +0x6e7
go/printer.func·005()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:172 +0x99

Previous write by goroutine 19:
go/token.(*FileSet).file()
/build/go.tip/go/src/pkg/go/token/position.go:379 +0x17b
go/token.(*FileSet).Position()
/build/go.tip/go/src/pkg/go/token/position.go:403 +0x70
go/printer.(*printer).posFor()
/build/go.tip/go/src/pkg/go/printer/printer.go:142 +0x58
go/printer.(*printer).nextComment()
/build/go.tip/go/src/pkg/go/printer/printer.go:121 +0x246
go/printer.(*printer).printNode()
/build/go.tip/go/src/pkg/go/printer/printer.go:1028 +0x4c0
go/printer.(*Config).fprint()
/build/go.tip/go/src/pkg/go/printer/printer.go:1196 +0xbe
go/printer.(*Config).Fprint()
/build/go.tip/go/src/pkg/go/printer/printer.go:1254 +0x89
go/printer.format()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:62 +0x3fc
go/printer.runcheck()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:123 +0x19e
go/printer.func·005()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:172 +0x99

Goroutine 17 (running) created at:
go/printer.check()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:174 +0x1a2
go/printer.TestFiles()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:209 +0x294
testing.tRunner()
/build/go.tip/go/src/pkg/testing/testing.go:301 +0xe8

Goroutine 19 (running) created at:
go/printer.check()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:174 +0x1a2
go/printer.TestFiles()
/build/go.tip/go/src/pkg/go/printer/printer_test.go:209 +0x294
testing.tRunner()
/build/go.tip/go/src/pkg/testing/testing.go:301 +0xe8

==================
--- FAIL: TestFiles-123 (30.73 seconds)
printer_test.go:180: testdata/expressions.input: running too slowly
printer_test.go:180: testdata/expressions.input: running too slowly
FAIL
FAIL go/printer 68.221s

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

6g

Which operating system are you using?

linux

Which version are you using? (run 'go version')

3fe40a41018d

Issue 2:
As per Rob and Andrew's request:
https://groups.google.com/forum/#!topic/golang-nuts/Q7lwBDPmQh4