debug: handle storage-free Python attributes

cl/compile_test.go

@@ -412,6 +412,13 @@ func TestRunAndTestFromTestpy(t *testing.T) {
 	cltest.RunAndTestFromDir(t, "", "./_testpy", nil)
 }
 
+func TestRunAndTestFromTestpyDWARF(t *testing.T) {
+	conf := build.NewDefaultConf(build.ModeRun)
+	conf.LinkOptions.DWARF = build.DWARFPreserve
+	cltest.RunAndTestFromDir(t, "", "./_testpy", nil,
+		cltest.WithRunConfig(conf), cltest.WithIRCheck(false))
+}
+
 func TestRunAndTestFromTestlibgo(t *testing.T) {
 	cltest.RunAndTestFromDir(t, "", "./_testlibgo", nil)
 }

ssa/di.go

@@ -769,6 +769,11 @@ const (
 )
 
 func (b Builder) DIGlobal(v Expr, name string, pos token.Position) {
+	// Frontend pseudo-variables, such as Python module attributes, have no
+	// native storage to describe or attach metadata to.
+	if v.impl.IsNil() {
+		return
+	}
 	if _, ok := b.Pkg.glbDbgVars[v]; ok {
 		return
 	}

ssa/di_debug_test.go

@@ -166,6 +166,11 @@ type Shape struct {
 	}
 }
 
+func TestDIGlobalIgnoresStorageLessFrontendVariable(t *testing.T) {
+	var builder Builder
+	builder.DIGlobal(pyVarExpr(Nil, "attribute"), "module.attribute", token.Position{})
+}
+
 func newDebugRuntimePackage() *types.Package {
 	pkg := types.NewPackage(PkgRuntime, "runtime")
 	unsafePointer := types.Typ[types.UnsafePointer]