gopls/internal/golang: Rename: fix crash in ill-typed redeclaration

+ test

Fixes golang/go#70968

Change-Id: I5d446dc3d4bd530a73565a17c12fa875bf25cfd0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/663915
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

Author: adonovan

gopls/internal/golang/rename_check.go

@@ -472,14 +472,15 @@ func (r *renamer) checkStructField(from *types.Var) {
 			// This struct is also a named type.
 			// We must check for direct (non-promoted) field/field
 			// and method/field conflicts.
-			named := r.pkg.TypesInfo().Defs[spec.Name].Type()
-			prev, indices, _ := types.LookupFieldOrMethod(named, true, r.pkg.Types(), r.to)
-			if len(indices) == 1 {
-				r.errorf(from.Pos(), "renaming this field %q to %q",
-					from.Name(), r.to)
-				r.errorf(prev.Pos(), "\twould conflict with this %s",
-					objectKind(prev))
-				return // skip checkSelections to avoid redundant errors
+			if tname := r.pkg.TypesInfo().Defs[spec.Name]; tname != nil {
+				prev, indices, _ := types.LookupFieldOrMethod(tname.Type(), true, r.pkg.Types(), r.to)
+				if len(indices) == 1 {
+					r.errorf(from.Pos(), "renaming this field %q to %q",
+						from.Name(), r.to)
+					r.errorf(prev.Pos(), "\twould conflict with this %s",
+						objectKind(prev))
+					return // skip checkSelections to avoid redundant errors
+				}
 			}
 		} else {
 			// This struct is not a named type.

gopls/internal/test/marker/testdata/rename/issue70968.txt

@@ -0,0 +1,20 @@
+Test that an (ill-typed) redeclaration of a name, which causes
+types.Info.Defs to lack an entry, doesn't lead to gopls to crash in
+renaming. Now, it proceeds with a partial rename.
+
+See golang/go#70968
+
+-- go.mod --
+module example.com
+go 1.18
+
+-- a/a.go --
+package a
+
+type T int               //@ diag("T", re"T redeclared")
+type T struct { f int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)
+
+-- @out/a/a.go --
+@@ -4 +4 @@
+-type T struct { f int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)
++type T struct { g int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)