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ALTree opened this issue Jul 20, 2016 · 9 comments
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cmd/compile: compiler panics on key-element slice literal with float index #16439

ALTree opened this issue Jul 20, 2016 · 9 comments
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@ALTree
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ALTree commented Jul 20, 2016 

go version devel +883e128 Wed Jul 20 05:08:37 2016 +0000 linux/amd64

The compiler knows that you must use an integer constant as an index for a key-element literal, and the error message is fine when a negative index is used:

package main

func main() {
    _ = []int{-1: 3}
}

./prova.go:4: index must be non-negative integer constant

but the compiler panics when a float is used:

package main

func main() {
    _ = []int{-1.0: 3}
}

# command-line-arguments
panic: interface conversion: interface {} is *gc.Mpflt, not *gc.Mpint

goroutine 1 [running]:
panic(0x8b5cc0, 0xc4204109c0)
    /home/alberto/go/src/runtime/panic.go:500 +0x1a1
cmd/compile/internal/gc.nonnegconst(0xc42041e510, 0x2)
    /home/alberto/go/src/cmd/compile/internal/gc/const.go:1494 +0x17a
cmd/compile/internal/gc.typecheckcomplit(0xc42041e3f0, 0x0)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:2906 +0x34f
cmd/compile/internal/gc.typecheck1(0xc42041e3f0, 0x2, 0xc42001d3b0)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:823 +0x57e8
cmd/compile/internal/gc.typecheck(0xc42041e3f0, 0x2, 0xc42001d3b0)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x654
cmd/compile/internal/gc.typecheckas(0xc42041e750)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:3210 +0xa9
cmd/compile/internal/gc.typecheck1(0xc42041e750, 0x1, 0xb07570)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:1952 +0x3bee
cmd/compile/internal/gc.typecheck(0xc42041e750, 0x1, 0x0)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x654
cmd/compile/internal/gc.typecheckslice(0xc42002e758, 0x1, 0x1, 0x1)
    /home/alberto/go/src/cmd/compile/internal/gc/typecheck.go:49 +0x57
cmd/compile/internal/gc.Main()
    /home/alberto/go/src/cmd/compile/internal/gc/main.go:389 +0x178d
cmd/compile/internal/amd64.Main()
    /home/alberto/go/src/cmd/compile/internal/amd64/galign.go:93 +0x2fa
main.main()
    /home/alberto/go/src/cmd/compile/main.go:33 +0x2a3
@ALTree ALTree changed the title cmd/compile: compiler panic on key-element slice literal with float index cmd/compile: compiler panics on key-element slice literal with float index Jul 20, 2016
@odeke-em
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I've sent a CL https://go-review.googlesource.com/#/c/25081.

@gopherbot
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CL https://golang.org/cl/25081 mentions this issue.

@ALTree
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ALTree commented Jul 20, 2016

That was fast; I opened the issue to provide a reference to a patch I wanted to mail (it's CL 25090, gobot didn't reference it here since I closed it with R=go1.8).

Well, we can now choose between two different fixes.

@ianlancetaylor ianlancetaylor added this to the Go1.8 milestone Jul 20, 2016
@josharian
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FWIW, I prefer CL 25090.

nonnegconst could use a bit of cleanup, but that's unrelated...and that's true for much of the compiler.

@odeke-em
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Thanks @ALTree. @josharian aye aye, yap I now see that too, CL 25090 is smaller, less invasive and will prevent other crashes that slip through in that check. I considered one like it but thought I could somewhat improve the message since 'non-negative integer' seems like a catch all statement IMO but it might just be sufficient.

@josharian
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@odeke-em yep, I think it's sufficient. I'm thrilled to see more folks working on the compiler, though. Please keep sending CLs!

@odeke-em
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Cool, I'll close my CL in favor of 25090 and we can move work to it. Awesome, I look forward to doing work on the compiler.

@griesemer
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For the record, a positive floating-point constant representable as an integer (e.g., 2.0) is permissible. Same for complex numbers representable as an integer (e.g., 2.0 + 0i). See my comments on https://go-review.googlesource.com/#/c/25090 .

@griesemer griesemer mentioned this issue Aug 12, 2016
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@gopherbot
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CL https://golang.org/cl/29011 mentions this issue.

@golang golang locked and limited conversation to collaborators Sep 26, 2017
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