gopls/internal/golang: fix crash in refactor.inline.variable

Fixes golang/go#74347

Change-Id: I19c38eec92c61e611c5112ae83e2c084c7954a14
Reviewed-on: https://go-review.googlesource.com/c/tools/+/683535
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>

Author: adonovan

gopls/internal/golang/inline.go

@@ -21,6 +21,7 @@ import (
 	"golang.org/x/tools/gopls/internal/cache"
 	"golang.org/x/tools/gopls/internal/cache/parsego"
 	"golang.org/x/tools/gopls/internal/protocol"
+	goplsastutil "golang.org/x/tools/gopls/internal/util/astutil"
 	"golang.org/x/tools/gopls/internal/util/safetoken"
 	"golang.org/x/tools/internal/diff"
 	"golang.org/x/tools/internal/event"
@@ -196,6 +197,12 @@ func inlineVariableOne(pkg *cache.Package, pgf *parsego.File, start, end token.P
 		}
 		id := curIdent.Node().(*ast.Ident)
 		obj1 := info.Uses[id]
+		if obj1 == nil {
+			continue // undefined; or a def, not a use
+		}
+		if goplsastutil.NodeContains(curRHS.Node(), obj1.Pos()) {
+			continue // not free (id is defined within RHS)
+		}
 		_, obj2 := scope.LookupParent(id.Name, pos)
 		if obj1 != obj2 {
 			return nil, nil, fmt.Errorf("cannot inline variable: its initializer expression refers to %q, which is shadowed by the declaration at line %d", id.Name, safetoken.Position(pgf.Tok, obj2.Pos()).Line)

gopls/internal/test/marker/testdata/codeaction/inline-var-74347.txt

@@ -0,0 +1,20 @@
+This is a regressoon test of a crash in refactor.inline.variable.
+
+-- go.mod --
+module example.com/a
+go 1.18
+
+-- a/a.go --
+package a
+
+func _() {
+       x := func(notfree int) { _ = notfree }
+       println(x) //@codeaction("x", "refactor.inline.variable", result=out)
+}
+-- @out/a/a.go --
+package a
+
+func _() {
+       x := func(notfree int) { _ = notfree }
+       println(func(notfree int) { _ = notfree }) //@codeaction("x", "refactor.inline.variable", result=out)
+}