golang/go

cmd/vet: know what builtin functions have no side effects

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#22,851 opened on Nov 22, 2017

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Description

Reminder issue to continue the work in https://go-review.googlesource.com/c/go/+/79536.

For example, len and cap never have any side effects, and it would be useful to know that i == len(x) || i == len(x) is a suspicious expression.

More broadly, this could be extended to automatically detect what functions are free of side effects. But this would require having access to the full source with full type information, and may be complex and costly, so I'm not entirely sure it's a right fit for vet.

A simpler version of the above would be to also add standard library functions, such as strings.Contains or path.Join. I don't know if it is OK for vet to treat standard library packages differently, though.

Contributor guide

Research direction
Study the previous CL (https://go review.googlesource.com/c/go/+/79536) to understand the approach, then design a method to mark builtins like len and cap as side effect free. Consider how to extend to standard library functions without full type information, and discuss trade offs with the Go team.
Tech stack
go
Domain
backendtoolingdeveloper experience
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
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Stale
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Clear
Prerequisites
Gostatic analysis concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30