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cmd/compile: imag(0) is valid but not accepted #17446

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griesemer opened this issue Oct 14, 2016 · 5 comments
Closed

cmd/compile: imag(0) is valid but not accepted #17446

griesemer opened this issue Oct 14, 2016 · 5 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.9

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@griesemer
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package p
var _ = imag(0)

doesn't compile:

$ go tool compile y.go
y.go:2: invalid argument 0 (type int) for imag

But it's clearly accepted by the spec ("If the argument evaluates to an untyped constant, it must be a number, and the return value of the function is an untyped floating-point constant."). Both gotype and gccgo accept it.
@griesemer griesemer added this to the Go1.8 milestone Oct 14, 2016
@griesemer
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See also #17398 (indirectly related).

@griesemer griesemer self-assigned this Oct 14, 2016
@quentinmit quentinmit added the NeedsFix The path to resolution is known, but the work has not been done. label Oct 17, 2016
@rsc rsc modified the milestones: Go1.9, Go1.8 Oct 21, 2016
@odeke-em
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I think when we fix this issue, we should also pay attention to #11945 because fixing that mentioned issue will mean that
imag(0) will return an untyped value instead of a floating point constant not as the spec is quoted in #17446 (comment)

But it's clearly accepted by the spec ("If the argument evaluates to an untyped constant, it must be
a number, and the return value of the function is an untyped floating-point constant."). Both gotype 
and gccgo accept it.

@josharian
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When we test this, make sure to test real too: const x = real(0). (go-fuzz just re-found this bug.)

@gopherbot
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CL https://golang.org/cl/45076 mentions this issue.

gopherbot pushed a commit that referenced this issue Jun 7, 2017
@griesemer
cmd/compile: separate code for len, cap from code for real, imag
d8899ac 
Prep work for issues mentioned below. No semantic or functionality change.

For #11945.
For #17446.

Change-Id: Ia1bb2b87647a6daa47f7863c0eb42cf5e1d35a7c
Reviewed-on: https://go-review.googlesource.com/45076
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
@gopherbot
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CL https://golang.org/cl/45081 mentions this issue.

@golang golang locked and limited conversation to collaborators Jun 8, 2018
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.9
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@josharian @rsc @quentinmit @odeke-em @griesemer @gopherbot