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compiler/prelude: Keep nil slice nil when slicing. #852

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Merged
merged 2 commits into from
Aug 20, 2018
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compiler/prelude: Keep nil slice nil when slicing. #852

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compiler/prelude: Keep nil slice nil when slicing.
dmitshur Aug 20, 2018
4ec9ef5
tests: Improve test error message consistency.
dmitshur Aug 20, 2018
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tests: Improve test error message consistency. 
Use the more common "got <x>, want <y>" style.
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@dmitshur
dmitshur committed Aug 20, 2018
commit 4ec9ef5604f49d66f23be2c94ae5af9687edd32c
14 changes: 11 additions & 3 deletions tests/misc_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -641,16 +641,24 @@ func TestSlicingNilSlice(t *testing.T) {
t.Run("StaysNil", func(t *testing.T) {
var s []int
s = s[:]
if s != nil {
t.Errorf("nil slice became non-nil after slicing with s[:]: %#v, want []int(nil)", s)
}
s = nil
s = s[0:0]
if s != nil {
t.Errorf("nil slice became non-nil after slicing with s[0:0]: %#v, want []int(nil)", s)
}
s = nil
s = s[0:0:0]
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I'd add the same if s != nil above this

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Are you suggesting this in case one of the assigments makes s non-nil, but the following line makes it nil again, and we don't catch it?

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@hajimehoshi hajimehoshi Aug 20, 2018 •
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As s is expected to be nil, I thought you don't have to reassign nil, but probably reassiging would be better. Thanks!

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Yeah, I reassigned just to be sure that the error messages would be accurate if printed.

if s != nil {
t.Errorf("nil slice became non-nil after slicing: %#v", s)
t.Errorf("nil slice became non-nil after slicing with s[0:0:0]: %#v, want []int(nil)", s)
}
})
t.Run("Panics", func(t *testing.T) {
defer func() {
if err := recover(); err == nil || !strings.Contains(err.(error).Error(), "slice bounds out of range") {
t.Error("slicing nil slice out of range didn't panic as expected")
t.Error("slicing nil slice out of range didn't panic, want panic")
}
}()
var s []int
Expand All @@ -660,7 +668,7 @@ func TestSlicingNilSlice(t *testing.T) {
var s = []int{}
s = s[:]
if s == nil {
t.Errorf("non-nil slice became nil after slicing: %#v", s)
t.Errorf("non-nil slice became nil after slicing: %#v, want []int{}", s)
}
})
}