gopls/internal/golang: provide version info for stdlib methods

For golang/go#67159

Change-Id: If3d09a39e8bf0a5ab61dc0953d7250ad75525372
Reviewed-on: https://go-review.googlesource.com/c/tools/+/595135
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/golang/hover.go

@@ -1213,9 +1213,15 @@ func StdSymbolOf(obj types.Object) *stdlib.Symbol {
 		return nil
 	}
 
+	// Handle Function, Type, Const & Var.
 	if isPackageLevel(obj) {
+		// Symbols defined not in std lib package should return early.
+		symbols := stdlib.PackageSymbols[obj.Pkg().Path()]
+		if symbols == nil {
+			return nil
+		}
 		// TODO(hxjiang): This is binary searchable.
-		for _, s := range stdlib.PackageSymbols[obj.Pkg().Path()] {
+		for _, s := range symbols {
 			if s.Kind == stdlib.Method || s.Kind == stdlib.Field {
 				continue
 			}
@@ -1223,9 +1229,27 @@ func StdSymbolOf(obj types.Object) *stdlib.Symbol {
 				return &s
 			}
 		}
+		return nil
 	}
 
-	// TODO(hxjiang): handle exported fields and methods of package level types.
+	// Handle Method.
+	if fn, _ := obj.(*types.Func); fn != nil {
+		isPtr, named := typesinternal.ReceiverNamed(fn.Type().(*types.Signature).Recv())
+		if isPackageLevel(named.Obj()) {
+			for _, s := range stdlib.PackageSymbols[obj.Pkg().Path()] {
+				if s.Kind != stdlib.Method {
+					continue
+				}
+				ptr, recv, name := s.SplitMethod()
+				if ptr == isPtr && recv == named.Obj().Name() && name == fn.Name() {
+					return &s
+				}
+			}
+			return nil
+		}
+	}
+
+	// TODO(hxjiang): handle exported fields of package level types.
 	return nil
 }
 

gopls/internal/test/integration/misc/hover_test.go

@@ -669,6 +669,9 @@ package stdlib
 import "fmt"
 import "context"
 import "crypto"
+import "regexp"
+
+type testRegexp = *regexp.Regexp
 
 func _() {
 	var ctx context.Context
@@ -678,6 +681,11 @@ func _() {
 		fmt.Printf("%v", crypto.SHA512_224)
 	}
 	_ := fmt.Appendf(make([]byte, 100), "world, %d", 23)
+
+	var re = regexp.MustCompile("\n{2,}")
+	copy := re.Copy()
+	var testRE testRegexp
+	testRE.Longest()
 }
 `
 
@@ -692,7 +700,8 @@ func _() {
 		{"Canceled", true, "go1.7"},   // package-level var
 		{"Context", true, "go1.7"},    // package-level type
 		{"SHA512_224", true, "go1.5"}, // package-level const
-		// TODO(hxjiang): add test for symbol type Method.
+		{"Copy", true, "go1.6"},       // method
+		{"Longest", true, "go1.1"},    // method with alias receiver
 		// TODO(hxjiang): add test for symbol type Field.
 	}