cmd/gofmt: don't turn nil slices into empty slices during rewriting

The go/ast package uses and guarantees nil slices for optional
elements that weren't present in the parsed source code, such as the
list of return values of a function. Packages using go/ast rely on
this attribute and check for nils explicitly.

One such package is go/printer. In the presence of empty slices
instead of nil slices, it generates invalid code, such as "case :"
instead of "default:". The issues that this CL fixes are all
manifestations of that problem, each for a different syntactic

Fixes #33103
Fixes #33104
Fixes #33105

Change-Id: I219f95a7da820eaf697a4ee227d458ab6e4a80bd
Reviewed-by: Daniel Martí <>
Reviewed-by: Robert Griesemer <>
Run-TryBot: Daniel Martí <>
TryBot-Result: Gobot Gobot <>
3 files changed
tree: 041e7864794787f0ae254cc517b274920402c7ce
  1. .gitattributes
  2. .github/
  3. .gitignore
  11. api/
  12. doc/
  13. favicon.ico
  14. lib/
  15. misc/
  16. robots.txt
  17. src/
  18. test/

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