golang/go

reflect: Set: argument validation panics with ValueError, which is for receiver

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#41,953 opened on Oct 13, 2020

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Description

What version of Go are you using (go version)?

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

What did you do?

Pass a zero reflect.Value to Value.Set, as an argument.

https://play.golang.org/p/hynNVbNp4-L

What did you expect to see?

An error that puts the culprit on Value.Set's argument, not on its receiver. Something like:

panic: reflect: zero Value passed to reflect.Value.Set

What did you see instead?

A ValueError like this:

panic: reflect: call of reflect.Value.Set on zero Value

According to the docs:

A ValueError occurs when a Value method is invoked on a Value that does not support it. Such cases are documented in the description of each method.

But that's not what's really happening here. The receiving Value does support Set. It's the argument which is wrong.

Contributor guide

Research direction
Identify the location in reflect/value.go where Value.Set is defined and modify the argument validation to distinguish between a zero receiver and a zero argument, and adjust the error message accordingly.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75