Support complicated variable references

Bug: 226974242
Test: go test
Change-Id: Iaec16f5c498e7c75c9ee5d53d3499efadfba16bc

mk2rbc/mk2rbc.go

@@ -1270,7 +1270,28 @@ func (ctx *parseContext) parseReference(node mkparser.Node, ref *mkparser.MakeSt
 	// Handle only the case where the first (or only) word is constant
 	words := ref.SplitN(" ", 2)
 	if !words[0].Const() {
-		return ctx.newBadExpr(node, "reference is too complex: %s", refDump)
+		if len(words) == 1 {
+			expr := ctx.parseMakeString(node, ref)
+			return &callExpr{
+				object: &identifierExpr{"cfg"},
+				name:   "get",
+				args: []starlarkExpr{
+					expr,
+					&callExpr{
+						object: &identifierExpr{"g"},
+						name:   "get",
+						args: []starlarkExpr{
+							expr,
+							&stringLiteralExpr{literal: ""},
+						},
+						returnType: starlarkTypeUnknown,
+					},
+				},
+				returnType: starlarkTypeUnknown,
+			}
+		} else {
+			return ctx.newBadExpr(node, "reference is too complex: %s", refDump)
+		}
 	}
 
 	if name, _, ok := ctx.maybeParseFunctionCall(node, ref); ok {

mk2rbc/mk2rbc_test.go

@@ -1597,6 +1597,27 @@ MY_VAR := foo
 def init(g, handle):
   cfg = rblf.cfg(handle)
   g["MY_VAR"] = "foo"
+`,
+	},
+	{
+		desc:   "Complicated variable references",
+		mkname: "product.mk",
+		in: `
+MY_VAR := foo
+MY_VAR_2 := MY_VAR
+MY_VAR_3 := $($(MY_VAR_2))
+MY_VAR_4 := $(foo bar)
+MY_VAR_5 := $($(MY_VAR_2) bar)
+`,
+		expected: `load("//build/make/core:product_config.rbc", "rblf")
+
+def init(g, handle):
+  cfg = rblf.cfg(handle)
+  g["MY_VAR"] = "foo"
+  g["MY_VAR_2"] = "MY_VAR"
+  g["MY_VAR_3"] = (cfg).get(g["MY_VAR_2"], (g).get(g["MY_VAR_2"], ""))
+  g["MY_VAR_4"] = rblf.mk2rbc_error("product.mk:5", "cannot handle invoking foo")
+  g["MY_VAR_5"] = rblf.mk2rbc_error("product.mk:6", "reference is too complex: $(MY_VAR_2) bar")
 `,
 	},
 }