golang/go

cmd/vet: make printf checking more precise when arguments are changed

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#26,555 opened on Jul 23, 2018

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Description

For #26486 https://golang.org/cl/125039 changed the printf checking to only warn about functions that do not modify the arguments before passing them to fmt.Printf (or whatever). The example in that issue, drawn from real code, is:

func dbg(s string, va ...interface{}) {
	if s == "" {
		s = strings.Repeat("%v ", len(va))
	}
	_, fn, fl, _ := runtime.Caller(1)
	fmt.Printf("dbg %s:%d: ", path.Base(fn), fl)
	fmt.Printf(s, va...)
	fmt.Println()
}

This can be called as dbg("", err).

The fix in CL 125039 means that we no longer issue printf warnings for functions like this:

func Prefix(s string, args ...interface{}) {
    s = "error: " + s
    fmt.Printf(s, args)
}

We should figure out a way to continue issuing warnings for Prefix without issuing them for dbg.

Contributor guide

Research direction
Examine the current implementation in cmd/vet/printf.go and understand the flag introduced in CL 125039. Then devise a method to distinguish between functions that unconditionally modify arguments (like Prefix) and those that conditionally modify (like dbg). This may involve tracking control flow and assignment to the format string before the printf call.
Tech stack
go
Domain
tooling
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.
1-2 days
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.
35