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cmd/compile: confusing error messages when a type is repeated #8853

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btracey opened this issue Oct 2, 2014 · 8 comments
Open

cmd/compile: confusing error messages when a type is repeated #8853

btracey opened this issue Oct 2, 2014 · 8 comments
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Suggested Issues that may be good for new contributors looking for work to do.
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@btracey
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btracey commented Oct 2, 2014 

Code:
http://play.golang.org/p/MoahP8X1aD

If a type is defined twice in a given package, this can lead to unfortunate interface
assignment errors. As an example, in the code above, "type Foo int" exists
twice. The error message is

prog.go:9: Foo redeclared in this block
    previous declaration at prog.go:3
prog.go:18: cannot convert Bar literal (type Bar) to type Fooer:
    Bar does not implement Fooer (wrong type for Foo method)
        have Foo() Foo
        want Foo() Foo

In this particular case it's fine because the "Foo redeclared" error comes
first, but in my actual code the interface conversion error was returned first and then
there were more errors before the redeclaration error.
@ianlancetaylor
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Comment 1:

Labels changed: added repo-main, release-none, suggested.

Status changed to Accepted.

@btracey btracey added accepted Suggested Issues that may be good for new contributors looking for work to do. labels Oct 2, 2014
@pwaller pwaller mentioned this issue Jan 21, 2015
Open
@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@rsc rsc changed the title cmd/gc: confusing error messages when a type is repeated cmd/compile: confusing error messages when a type is repeated Jun 8, 2015
@agnivade
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@btracey - Can you post the code where you got the interface conversion error before the redeclaration error ? And possibly those "more errors".

In my testing, the errors come linearly in the order in which they are written in the source code. If I redeclare before trying to convert the interface, it gives me the redeclaration error before. Vice-versa, it gives the interface conversion error before. This seems like reasonable behavior to me.

@agnivade agnivade added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Jun 16, 2018
@gopherbot
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Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)

@btracey
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btracey commented Jul 16, 2018

Sorry, this bug report is from a long time ago and I don't have any memory of what the code would have been. I believe though that the problem was I had a many compile errors, and so I was only getting the error saying the interface type can't be converted, and the redeclared error. was not printed

@odeke-em odeke-em reopened this Jul 16, 2018
@btracey
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btracey commented Jul 16, 2018

The issue is that the

        have Foo() Foo
        want Foo() Foo

Is very confusing. It would be better to not print, or print something else, if the strings are identical

@ianlancetaylor ianlancetaylor removed the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Jul 16, 2018
@ianlancetaylor
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@agnivade We should not be printing

    have Foo() Foo
    want Foo() Foo

That is not helpful at any level. We should suppress that error for duplicate types, given that the duplicate type is already going to cause an error.

@agnivade
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Ah, thank you for the clarification. I thought the issue was about the order of the errors.

@smasher164
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Is interface conversion the only place where this problem can appear? If so, would it be enough to return OCONVIFACE in assignop when the have and want strings match? This is considering the fact that the typechecker only reports the mentioned error when the returned Op == 0.

@odeke-em odeke-em self-assigned this Jun 7, 2020
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