Proposal: Cmd/vet: Add Check For Using %q With Integer Types

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Proposal Details

As part of our ongoing efforts to improve the Go programming language, we propose adding a check to the cmd/vet tool to warn about using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This proposal is inspired by the recent addition of a Go vet warning for string(i), which has the surprising behavior of returning the character with that integer code, as opposed to doing what strconv.Itoa does.

Background

The %q format verb is used to print a Go-quoted string representation of its argument. However, when used with integer types, it can produce unexpected results. For example, fmt.Printf("%q", 123) prints the character '{', which is the ASCII code for the integer 123. This behavior is not what most developers would expect, and it can lead to bugs and confusion.

Problem Statement

The current implementation of the %q format verb does not provide any warnings or errors when used with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This can lead to unexpected behavior and bugs in Go programs.

Proposed Solution

To address this issue, we propose adding a check to the cmd/vet tool to warn about using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This check would be similar to the one added for string(i), and would provide a clear warning to developers about the potential issues with using %q with integer types.

Implementation

The implementation of this proposal would involve adding a new check to the cmd/vet tool. This check would be responsible for detecting when the %q format verb is used with an integer type that does not implement error, fmt.Stringer, or fmt.Formatter. When such a case is detected, the check would emit a warning to the developer.

Example Use Case

Here is an example of how the proposed check would work:

package main

import (
	"fmt"
)

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

In this example, the cmd/vet tool would emit a warning because the %q format verb is used with an integer type (the int type) that does not implement error, fmt.Stringer, or fmt.Formatter.

Benefits

The proposed check would provide several benefits to Go developers. First, it would help to prevent bugs and unexpected behavior caused by using the %q format verb with integer types. Second, it would provide a clear warning to developers about the potential issues with using %q with integer types, making it easier for them to write correct and reliable code.

Alternatives

There are several alternatives to the proposed check. One alternative would be to change the behavior of the %q format verb to always return a string representation of the integer type, rather than a Go-quoted string representation. However, this would likely break existing code that relies on the current behavior of %q. Another alternative would be to add a new format verb that provides a string representation of the integer type, but this would add additional complexity to the fmt package.

Conclusion

In conclusion, we propose adding a check to the cmd/vet tool to warn about using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This check would provide a clear warning to developers about the potential issues with using %q with integer types, and would help to prevent bugs and unexpected behavior caused by this issue.

Rationale

The rationale for this proposal is to improve the reliability and maintainability of Go programs by providing a clear warning to developers about the potential issues with using %q with integer types. By adding this check to the cmd/vet tool, we can help to prevent bugs and unexpected behavior caused by this issue, and make it easier for developers to write correct and reliable code.

Future Work

Future work on this proposal could involve adding additional checks to the cmd/vet tool to detect other potential issues with the %q format verb. For example, we could add a check to detect when the %q format verb is used with a type that does not implement fmt.Formatter, but does implement fmt.Stringer. We could also add a check to detect when the %q format verb is used with a type that does not implement fmt.Formatter or fmt.Stringer, but does implement error.

References

Q: What is the purpose of this proposal?

A: The purpose of this proposal is to add a check to the cmd/vet tool to warn about using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This check would provide a clear warning to developers about the potential issues with using %q with integer types, and would help to prevent bugs and unexpected behavior caused by this issue.

Q: Why is this proposal necessary?

A: This proposal is necessary because the current implementation of the %q format verb does not provide any warnings or errors when used with integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This can lead to unexpected behavior and bugs in Go programs.

Q: What types of integer types would be affected by this proposal?

A: This proposal would affect integer types that do not implement error, fmt.Stringer, or fmt.Formatter. This includes types such as int, uint, int8, uint8, int16, uint16, int32, uint32, int64, and uint64.

Q: How would the proposed check work?

A: The proposed check would involve adding a new function to the cmd/vet tool that would detect when the %q format verb is used with an integer type that does not implement error, fmt.Stringer, or fmt.Formatter. When such a case is detected, the check would emit a warning to the developer.

Q: What would the warning look like?

A: The warning would be similar to the one added for string(i), and would provide a clear indication to the developer that the %q format verb is being used with an integer type that does not implement error, fmt.Stringer, or fmt.Formatter.

Q: Would this proposal break existing code?

A: No, this proposal would not break existing code. The proposed check would only warn about using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter, and would not change the behavior of the %q format verb.

Q: What are the benefits of this proposal?

A: The benefits of this proposal include:

  • Preventing bugs and unexpected behavior caused by using the %q format verb with integer types that do not implement error, fmt.Stringer, or fmt.Formatter.
  • Providing a clear warning to developers about the potential issues with using %q with integer types.
  • Making it easier for developers to write correct and reliable code.

Q: What are the alternatives to this proposal?

A: There are several alternatives to this proposal, including:

  • Changing the behavior of the %q format verb to always return a string representation of the integer type, rather than a Go-quoted string representation.
  • Adding a new format verb that provides a string representation of the integer type.
  • Not adding any checks or warnings for using the %q format verb with integer types.

Q: What is the next step for this proposal?

A: The next step for this proposal is to implement the proposed check and add it to the cmd/vet tool. This would involve writing the necessary code and testing it to ensure that it works correctly.

Q: Who would be responsible for implementing this proposal?

A: The responsibility for implementing this proposal would fall on the Go team, specifically the cmd/vet tool maintainers.

Q: What is the timeline for implementing this proposal?

A: The timeline for implementing this proposal is not yet determined, but it is expected to be completed within the next few months.

Q: How can I get involved in this proposal?

A: If you are interested in getting involved in this proposal, you can start by reviewing the proposal and providing feedback. You can also join the Go team's mailing list and participate in the discussion.