x/tools/gopls/internal/analysis/modernize: apply modernizations for TrimPrefix to TrimSuffix too

[jakebailey]

I ran modernize on typescript-go, which caught this code:

if str := strings.TrimPrefix(msg, "Found 'package.json' at '"); str != msg {
	// ...
}

And correctly turned it into:

if str, ok := strings.CutPrefix(msg, "Found 'package.json' at '"); ok {
	// ...
}

But, right above this code was this:

if str := strings.TrimSuffix(msg, "' does not exist."); str != msg {
	// ... 
}

That is, the same pattern, but with a suffix. This did not get modernized.

Based on https://github.com/golang/tools/blob/master/gopls/internal/analysis/modernize/stringscutprefix.go (especially its name), it looks as though these modernizations only apply to prefixes, not suffixes. It'd be great to have it in both directions, since the transformation seems about the same?

[gabyhelp]

Related Issues

• x/tools/gopls/internal/analysis/modernize: use strings.Cut #71369
• tools/gopls/internal/analysis/modernize: stringscutprefix offers invalid fix #73547 (closed)
• x/tools/gopls: modernize could suggest using strings.Cut* instead of strings.Split* #74494

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

[cuishuang]

Based on https://github.com/golang/tools/blob/master/gopls/internal/analysis/modernize/stringscutprefix.go (especially its name), it looks as though these modernizations only apply to prefixes, not suffixes. It'd be great to have it in both directions, since the transformation seems about the same?

Good idea, it sounds like it should be done that way.

I submitted a CL to add this feature.

If the proposal can be approved, I would be happy to help integrate it into the latest modernize analyzer.

[gopherbot]

Change https://go.dev/cl/701575 mentions this issue: gopls/internal/analysis/modernize: add StringsCutSuffixAnalyzer

[cuishuang]

Original code:

package trimSuffix

import "strings"

func main() {

	msg := "https://github.com/golang/go/issues/75205"

	if str := strings.TrimPrefix(msg, "Found 'package.json' at '"); str != msg {
		print(str)
	}

	if str := strings.TrimSuffix(msg, "' does not exist."); str != msg {
		print(str)
	}

}

Code processed by the analyzer:

package trimSuffix

import "strings"

func main() {

	msg := "https://github.com/golang/go/issues/75205"

	if str, ok := strings.CutPrefix(msg, "Found 'package.json' at '"); ok {
		print(str)
	}

	if str, ok := strings.CutSuffix(msg, "' does not exist."); ok {
		print(str)
	}

}

[adonovan]

Fixed by https://go.dev/cl/701575 .