proposal: cmd/vet: add check for using %q with integer types

[rittneje]

Proposal Details

#32479 added a go vet warning for string(i), because it has the surprising behavior of returning the character with that integer code, as opposed to doing what strconv.Itoa does.

There is another similar case, where someone uses the %q format verb like so:

fmt.Printf("%q", 123) // prints '{'

Consequently, it would be helpful if go vet also warned about using %q with an integer type that does not implement error, fmt.Stringer, or fmt.Formatter.

[ianlancetaylor]

CC @golang/tools-team

[gabyhelp]

Related Issues

• cmd/vet: printf %q with pointer argument not detected #25233 (closed)
• cmd/vet: should not complain about format %q used with []string #25869 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[adonovan]

How would you distinguish the intended uses of the documented feature

%q a single-quoted character literal safely escaped with Go syntax.

from the unintended ones? Would you require that the integer operand is exactly a byte or rune?

[rittneje]

@adonovan My intention was for this to be natural extension of the existing printf and stringintconv checks. It seems the latter does specifically allow for byte, uint8, and rune (and typedefs on them), so for consistency I suppose the proposed check ought to do the same.

[adonovan]

Would you like to send a CL to make the necessary change?

[rittneje]

@adonovan I can try, but I have little experience writing analysis tools. Do you think this new check should be folded into the existing printf check, or a new check?

[adonovan]

@adonovan I can try, but I have little experience writing analysis tools. Do you think this new check should be folded into the existing printf check, or a new check?

It should be part of the existing printf check, but I just remembered that we recently decided that all new checks added to existing analyzers need to respect the applicable language version of Go in the file being analyzed. This will make the change more subtle than simply modifying an entry in a table of pairs such as ("%q", int), so it may be best tackled by someone already comfortable in x/tools.

[adonovan]

Attached file shows 42976 hits of the new check across ~10,000 modules.

printf.txt

Here's a random 50 (though the sample seems very skewed toward hashicorp). I looked at a dozen of them by hand and all were true positives: places where the user seems to have used %q in place of %v, apparently unaware of Unicode. So I support this proposal.

(BTW the command I ran reports uses of %q, %c and %U with non-{byte,rune} integers. Only the uses of %q are real problems; the uses of %c and %U seem mostly correct, or at worst slightly confused but not really buggy. Clearly users don't reach for %c or %U unless they have some idea that they are dealing with code points.)

https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementgrouppolicymigrationreportidgrouppolicysettingmapping_test.go#L220: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/lingyao2333/mo-zero@v1.4.1/core/mapping/jsonunmarshaler_test.go#L287: (*testing.common).Fatalf format %q has arg c.People of wrong type []struct{Name string; Age int}
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_groupidthread_test.go#L205: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_useriddriveiditemidlistitempermission_test.go#L310: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/containerd/cgroups@v1.1.0/pids_test.go#L61: (*testing.common).Fatalf format %q has arg uint64(10) of wrong type uint64
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly/v6@v6.8.0/fastly/kafka_test.go#L113: (*testing.common).Errorf format %q has arg k.RequestMaxBytes of wrong type uint
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementoperationapprovalrequest_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_meonenotesection_test.go#L190: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementcomanagementeligibledevice_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly/v6@v6.8.0/fastly/syslog_test.go#L90: (*testing.common).Errorf format %q has arg s.Port of wrong type uint
https://go-mod-viewer.appspot.com/github.com/IBM-Cloud/bluemix-go@v0.0.0-20241117121028-a3be206688b3/session/session.go#L60: fmt.Printf format %q has arg *c.MaxRetries of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly@v1.18.0/fastly/pubsub_test.go#L67: (*testing.common).Errorf format %q has arg pubsub.FormatVersion of wrong type uint
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementautopilotevent_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly@v1.18.0/fastly/digitalocean_test.go#L146: (*testing.common).Errorf format %q has arg digitalocean.Period of wrong type uint
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementdevicecompliancepolicyiddevicestatus_test.go#L220: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementdeviceshellscriptiddevicerunstate_test.go#L220: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_useridjoinedteamidchannel_test.go#L250: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/gopkg.in/asaskevich/govalidator.v9@v9.0.0-20180315120708-ccb8e960c48f/utils_test.go#L499: (*testing.common).Errorf format %q has arg test.param3 of wrong type int
https://go-mod-viewer.appspot.com/github.com/Psiphon-Labs/net@v0.0.0-20191204183604-f5d60dada742/websocket/hybi_test.go#L193: (*testing.common).Errorf format %q has arg http.StatusSwitchingProtocols of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_devicemanagementimportedwindowsautopilotdeviceidentity_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/containerd/cgroups@v1.1.0/pids_test.go#L82: (*testing.common).Fatalf format %q has arg uint64(5) of wrong type uint64
https://go-mod-viewer.appspot.com/github.com/vbatts/tar-split@v0.12.1/tar/asm/iterate.go#L54: fmt.Errorf format %q has arg tsEntry.Type of wrong type github.com/vbatts/tar-split/tar/storage.Type
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_devicemanagementuserexperienceanalyticsscorehistory_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_useridoutlooktaskgroupidtaskfolderidtaskidattachment_test.go#L355: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_identitygovernancelifecycleworkflowdeleteditemworkflowidtask_test.go#L250: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_meappconsentrequestsforapprovaliduserconsentrequest_test.go#L220: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_directoryadministrativeunit_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/jurgen-kluft/ccode@v0.0.0-20250310085352-03c5a49627e7/axe/axe-topological-sort.go#L95: fmt.Errorf format %q has arg cycleNodes of wrong type []github.com/jurgen-kluft/ccode/axe.Vertex
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly/v5@v5.3.0/fastly/cloudfiles_test.go#L328: (*testing.common).Errorf format %q has arg cloudfilesUpdateResp1.Period of wrong type uint
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_groupidowner_test.go#L205: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly@v1.18.0/fastly/syslog_test.go#L90: (*testing.common).Errorf format %q has arg s.Port of wrong type uint
https://go-mod-viewer.appspot.com/github.com/vbatts/go-mtree@v0.5.4/pkg/govis/vis_test.go#L39: (*testing.common).Errorf format %q has arg test of wrong type struct{input string; flag github.com/vbatts/go-mtree/pkg/govis.VisFlag}
https://go-mod-viewer.appspot.com/go.chromium.org/luci@v0.0.0-20250314024836-d9a61d0730e6/buildbucket/appengine/model/build.go#L534: go.chromium.org/luci/common/errors.Annotate format %q has arg p.Id of wrong type int64
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_devicemanagementuserexperienceanalyticsworkfromanywheremetric_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_identitygovernanceentitlementmanagementaccesspackageassignmentidaccesspackageaccesspackageassignmentpolicy_test.go#L250: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/gopkg.in/rethinkdb/rethinkdb-go.v6@v6.2.2/encoding/encoder_test.go#L274: (*testing.common).Errorf format %q has arg want of wrong type map[string]int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_medriveidlistcontenttypeidbasetype_test.go#L280: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_meeventidexceptionoccurrenceidattachment_test.go#L265: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_devicemanagementhardwareconfigurationidassignment_test.go#L220: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_useridjoinedteamidprimarychanneltab_test.go#L265: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_groupiddriveiditemidlistitemdocumentsetversion_test.go#L310: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_useridjoinedteamidscheduleopenshift_test.go#L265: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly/v5@v5.3.0/fastly/pool_test.go#L56: (*testing.common).Errorf format %q has arg p.Quorum of wrong type uint
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_groupidsiteidonenotenotebookidsection_test.go#L310: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_directoryimpactedresource_test.go#L175: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/beta/id_memailfolderidmessageidattachment_test.go#L265: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_useriddriveidlistcolumn_test.go#L265: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/hashicorp/go-azure-sdk/microsoft-graph@v0.20250310.1130319/common-types/stable/id_mejoinedteamidscheduleopenshiftchangerequest_test.go#L235: (*testing.common).Fatalf format %q has arg len(uniqueNames) of wrong type int
https://go-mod-viewer.appspot.com/github.com/fastly/go-fastly/v5@v5.3.0/fastly/papertrail_test.go#L104: (*testing.common).Errorf format %q has arg p.Port of wrong type uint
https://go-mod-viewer.appspot.com/github.com/rootless-containers/rootlesskit/v2@v2.3.4/pkg/port/portutil/portutil.go#L139: fmt.Errorf format %q has arg spec.ChildPort of wrong type int

[gopherbot]

Change https://go.dev/cl/657957 mentions this issue: go/analysis/passes/printf: disallow %q of int