gopls/internal/analysis/modernize: replace loop with slices.Contains

This CL adds a modernizer pass for slices.Contains{,Func}.

Example:

func assignTrueBreak(slice []int, needle int) {
	found := false
	for _, elem := range slice { // want "Loop can be simplified using strings.Contains"
		if elem == needle {
			found = true
			break
		}
	}
	print(found)
}

=>

func assignTrueBreak(slice []int, needle int) {
	found := slices.Contains(slice, needle)
	print(found)
}

Updates golang/go#70815

Change-Id: I72ad1c099481b6c9ae6f732e2d81674a98b79a9f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/640576
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Commit-Queue: Alan Donovan <[email protected]>

Author: adonovan

gopls/internal/analysis/modernize/modernize.go

@@ -49,6 +49,9 @@ func run(pass *analysis.Pass) (any, error) {
 		}
 		report := pass.Report
 		pass.Report = func(diag analysis.Diagnostic) {
+			if diag.Category == "" {
+				panic("Diagnostic.Category is unset")
+			}
 			if _, ok := generated[pass.Fset.File(diag.Pos)]; ok {
 				return // skip checking if it's generated code
 			}
@@ -62,6 +65,7 @@ func run(pass *analysis.Pass) (any, error) {
 	fmtappendf(pass)
 	mapsloop(pass)
 	minmax(pass)
+	slicescontains(pass)
 	sortslice(pass)
 	testingContext(pass)
 
@@ -120,7 +124,9 @@ var (
 	builtinAny    = types.Universe.Lookup("any")
 	builtinAppend = types.Universe.Lookup("append")
 	builtinBool   = types.Universe.Lookup("bool")
+	builtinFalse  = types.Universe.Lookup("false")
 	builtinMake   = types.Universe.Lookup("make")
 	builtinNil    = types.Universe.Lookup("nil")
+	builtinTrue   = types.Universe.Lookup("true")
 	byteSliceType = types.NewSlice(types.Typ[types.Byte])
 )

gopls/internal/analysis/modernize/modernize_test.go

@@ -19,6 +19,7 @@ func Test(t *testing.T) {
 		"fmtappendf",
 		"mapsloop",
 		"minmax",
+		"slicescontains",
 		"sortslice",
 		"testingcontext",
 	)

gopls/internal/analysis/modernize/slices.go

@@ -5,6 +5,7 @@
 package modernize
 
 // This file defines modernizers that use the "slices" package.
+// TODO(adonovan): actually let's split them up and rename this file.
 
 import (
 	"fmt"