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cmd/vet: printf %q with pointer argument not detected #25233

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rudis opened this issue May 3, 2018 · 3 comments

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@rudis
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commented May 3, 2018

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

go version go1.10.1 linux/amd64

Does this issue reproduce with the latest release?

Yes. Also in Git master as of 2018-05-03.

What did you do?

package main
import (
        "fmt"
)
func main() {
        x := "hi"
        y := &x
        fmt.Printf("%q\n", y)
}

The programs prints %!q(*string=0xc42000e1e0) but go vet prints no error message.

What did you expect to see?

go vet detects the error.

The problem seems to be the type classification which marks %q as argRune|argInt|argString, this causes the check in cmd/vet/types.go matchArgTypeInternal() (under case *types.Pointer) to consider y (from code above) as valid int, although this won't work with pointers for %q.

A potential patch could look like this. However it feels ugly and therefor wasn't submitted as pull request:

--- types.go.orig       2018-05-03 13:06:45.151615943 +0200
+++ types.go    2018-05-03 13:08:09.414532090 +0200
@@ -201,6 +201,10 @@
                if str, ok := typ.Elem().Underlying().(*types.Struct); ok {
                        return f.matchStructArgType(t, str, arg, inProgress)
                }
+               // %q can't print pointers.
+               if t == (argRune|argInt|argString) {
+                       return false
+               }
                // The rest can print with %p as pointers, or as integers with %x etc.
                return t&(argInt|argPointer) != 0
@ALTree

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commented May 3, 2018

@ALTree ALTree added this to the Go1.11 milestone May 3, 2018

@mvdan

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commented May 3, 2018

I've been poking around in the vet codebase for a bit, and I think it's simply inconsistent with fmt's documentation and code. I'm going to submit a CL soon, which solves the issue that @rudis is having, and I believe also fixes other inconsistencies with fmt. The patch is different from the one proposed above, though.

@mvdan mvdan self-assigned this May 3, 2018

@gopherbot

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commented May 3, 2018

Change https://golang.org/cl/111284 mentions this issue: cmd/vet: better align print warnings with fmt

@gopherbot gopherbot closed this in 98409a4 May 4, 2018

@golang golang locked and limited conversation to collaborators May 4, 2019

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