gopls/internal/golang: fix bad slice append in function extraction

With multiple return statements, a slice append would overwrite the
return values of earlier returns. Fix by using slices.Concat.

For golang/go#66289

Change-Id: Ib23bcb9ff297aa1ce9511c7ae54e692b14facca7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/627537
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: findleyr

gopls/internal/golang/extract.go

@@ -12,6 +12,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"slices"
 	"sort"
 	"strings"
 	"text/scanner"
@@ -1214,10 +1215,14 @@ func generateReturnInfo(enclosing *ast.FuncType, pkg *types.Package, path []ast.
 			}
 			var name string
 			name, idx = generateAvailableIdentifier(pos, path, pkg, info, "returnValue", idx)
+			z := analysisinternal.ZeroValue(file, pkg, typ)
+			if z == nil {
+				return nil, nil, fmt.Errorf("can't generate zero value for %T", typ)
+			}
 			retVars = append(retVars, &returnVariable{
 				name:    ast.NewIdent(name),
 				decl:    &ast.Field{Type: expr},
-				zeroVal: analysisinternal.ZeroValue(file, pkg, typ),
+				zeroVal: z,
 			})
 		}
 	}
@@ -1250,8 +1255,7 @@ func adjustReturnStatements(returnTypes []*ast.Field, seenVars map[types.Object]
 			break
 		}
 		if val == nil {
-			return fmt.Errorf(
-				"could not find matching AST expression for %T", returnType.Type)
+			return fmt.Errorf("could not find matching AST expression for %T", returnType.Type)
 		}
 		zeroVals = append(zeroVals, val)
 	}
@@ -1266,7 +1270,7 @@ func adjustReturnStatements(returnTypes []*ast.Field, seenVars map[types.Object]
 			return false
 		}
 		if n, ok := n.(*ast.ReturnStmt); ok {
-			n.Results = append(zeroVals, n.Results...)
+			n.Results = slices.Concat(zeroVals, n.Results)
 			return false
 		}
 		return true

gopls/internal/test/marker/testdata/codeaction/functionextraction_issue66289.txt

@@ -0,0 +1,52 @@
+
+-- a.go --
+package a
+
+import (
+	"fmt"
+	"encoding/json"
+)
+
+func F() error {
+	a, err := json.Marshal(0) //@codeaction("a", end, "refactor.extract.function", out)
+	if err != nil {
+		return fmt.Errorf("1: %w", err)
+	}
+	b, err := json.Marshal(0)
+	if err != nil {
+		return fmt.Errorf("2: %w", err)
+	} //@loc(end, "}")
+	fmt.Println(a, b)
+	return nil
+}
+
+-- @out/a.go --
+package a
+
+import (
+	"fmt"
+	"encoding/json"
+)
+
+func F() error {
+	//@codeaction("a", end, "refactor.extract.function", out)
+	a, b, shouldReturn, returnValue := newFunction()
+	if shouldReturn {
+		return returnValue
+	} //@loc(end, "}")
+	fmt.Println(a, b)
+	return nil
+}
+
+func newFunction() ([]byte, []byte, bool, error) {
+	a, err := json.Marshal(0)
+	if err != nil {
+		return nil, nil, true, fmt.Errorf("1: %w", err)
+	}
+	b, err := json.Marshal(0)
+	if err != nil {
+		return nil, nil, true, fmt.Errorf("2: %w", err)
+	}
+	return a, b, false, nil
+}
+

internal/analysisinternal/analysis.go

@@ -80,9 +80,11 @@ func ZeroValue(f *ast.File, pkg *types.Package, typ types.Type) ast.Expr {
 		case under.Info()&types.IsNumeric != 0:
 			return &ast.BasicLit{Kind: token.INT, Value: "0"}
 		case under.Info()&types.IsBoolean != 0:
-			return &ast.Ident{Name: "false"}
+			return ast.NewIdent("false")
 		case under.Info()&types.IsString != 0:
 			return &ast.BasicLit{Kind: token.STRING, Value: `""`}
+		case under == types.Typ[types.Invalid]:
+			return nil
 		default:
 			panic(fmt.Sprintf("unknown basic type %v", under))
 		}