gopls/internal/analysis/fillstruct: use package name (not path) in UI

Also, factor out three instances of the type qualifier as
typesinternal.NameRelativeTo.

Change-Id: I22c1e8f89e77a7164c178cf335253a097b9850be
Reviewed-on: https://go-review.googlesource.com/c/tools/+/595119
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>

gopls/internal/analysis/fillstruct/fillstruct.go

@@ -29,6 +29,7 @@ import (
 	"golang.org/x/tools/internal/aliases"
 	"golang.org/x/tools/internal/analysisinternal"
 	"golang.org/x/tools/internal/typeparams"
+	"golang.org/x/tools/internal/typesinternal"
 )
 
 // Diagnose computes diagnostics for fillable struct literals overlapping with
@@ -89,7 +90,7 @@ func Diagnose(f *ast.File, start, end token.Pos, pkg *types.Package, info *types
 		var name string
 		if typ != tStruct {
 			// named struct type (e.g. pkg.S[T])
-			name = types.TypeString(typ, types.RelativeTo(pkg))
+			name = types.TypeString(typ, typesinternal.NameRelativeTo(pkg))
 		} else {
 			// anonymous struct type
 			totalFields := len(fillableFields)
@@ -159,7 +160,7 @@ func SuggestedFix(fset *token.FileSet, start, end token.Pos, content []byte, fil
 	tStruct, ok := typ.Underlying().(*types.Struct)
 	if !ok {
 		return nil, nil, fmt.Errorf("%s is not a (pointer to) struct type",
-			types.TypeString(typ, types.RelativeTo(pkg)))
+			types.TypeString(typ, typesinternal.NameRelativeTo(pkg)))
 	}
 	// Inv: typ is the possibly-named struct type.
 

gopls/internal/analysis/fillstruct/testdata/src/a/a.go

@@ -39,7 +39,7 @@ type nestedStruct struct {
 
 var _ = nestedStruct{} // want `nestedStruct literal has missing fields`
 
-var _ = data.B{} // want `b.B literal has missing fields`
+var _ = data.B{} // want `fillstruct.B literal has missing fields`
 
 type typedStruct struct {
 	m  map[string]int
@@ -100,10 +100,10 @@ type pointerBuiltinStruct struct {
 var _ = pointerBuiltinStruct{} // want `pointerBuiltinStruct literal has missing fields`
 
 var _ = []ast.BasicLit{
-	{}, // want `go/ast.BasicLit literal has missing fields`
+	{}, // want `ast.BasicLit literal has missing fields`
 }
 
-var _ = []ast.BasicLit{{}} // want "go/ast.BasicLit literal has missing fields"
+var _ = []ast.BasicLit{{}} // want "ast.BasicLit literal has missing fields"
 
 type unsafeStruct struct {
 	foo unsafe.Pointer

gopls/internal/golang/freesymbols.go

@@ -23,6 +23,7 @@ import (
 	"golang.org/x/tools/gopls/internal/util/maps"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/gopls/internal/util/slices"
+	"golang.org/x/tools/internal/typesinternal"
 )
 
 // FreeSymbolsHTML returns an HTML document containing the report of
@@ -49,14 +50,7 @@ func FreeSymbolsHTML(viewID string, pkg *cache.Package, pgf *parsego.File, start
 		Local    []Symbol
 	}
 
-	// TODO(adonovan): factor with RenderPackageDoc.
-	qualifier := func(other *types.Package) string {
-		// (like types.RelativeTo but using Package.Name)
-		if other == pkg.Types() {
-			return "" // same package; unqualified
-		}
-		return other.Name()
-	}
+	qualifier := typesinternal.NameRelativeTo(pkg.Types())
 
 	// Populate model.
 	{

gopls/internal/golang/pkgdoc.go

@@ -639,13 +639,7 @@ window.addEventListener('load', function() {
 	//   since it is unreachable for the methods in go/doc.
 	// - elides parameters after the first three: f(a, b, c, ...).
 	fnString := func(fn *types.Func) string {
-		// pkgRelative qualifies types by package name alone
-		pkgRelative := func(other *types.Package) string {
-			if pkg.Types() == other {
-				return "" // same package; unqualified
-			}
-			return other.Name()
-		}
+		pkgRelative := typesinternal.NameRelativeTo(pkg.Types())
 
 		sig := fn.Type().(*types.Signature)
 

internal/typesinternal/types.go

@@ -48,3 +48,18 @@ func ReadGo116ErrorData(err types.Error) (code ErrorCode, start, end token.Pos,
 	}
 	return ErrorCode(data[0]), token.Pos(data[1]), token.Pos(data[2]), true
 }
+
+// NameRelativeTo returns a types.Qualifier that qualifies members of
+// all packages other than pkg, using only the package name.
+// (By contrast, [types.RelativeTo] uses the complete package path,
+// which is often excessive.)
+//
+// If pkg is nil, it is equivalent to [*types.Package.Name].
+func NameRelativeTo(pkg *types.Package) types.Qualifier {
+	return func(other *types.Package) string {
+		if pkg != nil && pkg == other {
+			return "" // same package; unqualified
+		}
+		return other.Name()
+	}
+}