cmd/gofmt: not idempotent on line with multiple comments

[ALTree]

$ gotip version
go version devel +5f0a9ba134 Tue Mar 20 22:46:00 2018 +0000 linux/amd64

Note as the second gofmt invocation changes the code again:

$ cat test.go
package p

func f() {
	foo(); /* one */ fooooo(); /* two */
}

$ cat test.go | gofmt
package p

func f() {
	foo() /* one */
	fooooo() /* two */
}

$ cat test.go | gofmt | gofmt
package p

func f() {
	foo()    /* one */
	fooooo() /* two */

[ysmolski]

FYI, this break following test:

% go test cmd/gofmt
--- FAIL: TestAll (13.14s)
	long_test.go:88: gofmt /Users/thorn/golang/test/fixedbugs/issue22662.go not idempotent
FAIL
FAIL	cmd/gofmt	13.182s

[gopherbot]

Change https://golang.org/cl/130377 mentions this issue: cmd/gofmt: skip gofmt idempotency check on known issue

[ALTree]

The bad file tested fixedbugs/issue22662.go (which was causing failures in the std library test suite in TestAll when run without -short) is now skipped (CL 130377). The check should be re-enabled on that file when this issue is fixed.

[homuler]

It seems that this issue is caused by the following block.

go/src/go/printer/printer.go

Lines 383 to 388 in 3a7a528

	if pos.Line == next.Line {
	// next item is on the same line as the comment
	// (which must be a /*-style comment): separate
	// with a blank instead of a tab
	sep = ' '
	}

When the next token is on the same line as the comment, this appends a space character instead of \t.
However, the next token is not necessarily on the same line after formatting.