Remove variableDefinedExpr

VariableDefinedExpr was under-developed, and would not
take into account if a variable was from the globals
or product config dictionary.

It also always emitted `g.get("VARIABLE") != None`, which
is not correct behavior. In this example makefile:

```
MY_VAR :=

ifdef MY_VAR
$(info MY_VAR is defined)
else
$(info MY_VAR is not defined)
endif

ifdef MY_UNDEFINED_VAR
$(info MY_UNDEFINED_VAR is defined)
else
$(info MY_UNDEFINED_VAR is not defined)
endif

MY_VAR ?= true
MY_UNDEFINED_VAR ?= true


$(info MY_VAR after ?= is $(MY_VAR))
$(info MY_UNDEFINED_VAR after ?= is $(MY_UNDEFINED_VAR))


.PHONY: all
all:
	@:
```

We get the output:

MY_VAR is not defined
MY_UNDEFINED_VAR is not defined
MY_VAR after ?= is
MY_UNDEFINED_VAR after ?= is true

So we can see that even if a variable was set, it's considered
not defined if it was set to an empty value. However, ?= works
differently, and does require the != None, so that was left
as is.

Just use a variableRefExpr and rely on the fact
that variables will be truthy if they're defined.

Fixes: 216700361
Test: go test
Change-Id: If8944da2579e8658e3fc4f666b1f3b2815f8c8b1

mk2rbc/expr.go

@@ -378,32 +378,6 @@ func (eq *eqExpr) transform(transformer func(expr starlarkExpr) starlarkExpr) st
 	}
 }
 
-// variableDefinedExpr corresponds to Make's ifdef VAR
-type variableDefinedExpr struct {
-	v variable
-}
-
-func (v *variableDefinedExpr) emit(gctx *generationContext) {
-	if v.v != nil {
-		v.v.emitDefined(gctx)
-		return
-	}
-	gctx.writef("%s(%q)", cfnWarning, "TODO(VAR)")
-}
-
-func (_ *variableDefinedExpr) typ() starlarkType {
-	return starlarkTypeBool
-}
-
-func (v *variableDefinedExpr) emitListVarCopy(gctx *generationContext) {
-	v.emit(gctx)
-}
-
-func (v *variableDefinedExpr) transform(transformer func(expr starlarkExpr) starlarkExpr) starlarkExpr {
-	// TODO: VariableDefinedExpr isn't really an expression?
-	return v
-}
-
 type listExpr struct {
 	items []starlarkExpr
 }

mk2rbc/mk2rbc.go

@@ -1003,19 +1003,14 @@ func (ctx *parseContext) processBranch(check *mkparser.Directive) {
 	ctx.popReceiver()
 }
 
-func (ctx *parseContext) newIfDefinedNode(check *mkparser.Directive) (starlarkExpr, bool) {
-	if !check.Args.Const() {
-		return ctx.newBadExpr(check, "ifdef variable ref too complex: %s", check.Args.Dump()), false
-	}
-	v := ctx.addVariable(check.Args.Strings[0])
-	return &variableDefinedExpr{v}, true
-}
-
 func (ctx *parseContext) parseCondition(check *mkparser.Directive) starlarkNode {
 	switch check.Name {
 	case "ifdef", "ifndef", "elifdef", "elifndef":
-		v, ok := ctx.newIfDefinedNode(check)
+		if !check.Args.Const() {
-		if ok && strings.HasSuffix(check.Name, "ndef") {
+			return &exprNode{expr: ctx.newBadExpr(check, "ifdef variable ref too complex: %s", check.Args.Dump())}
+		}
+		v := NewVariableRefExpr(ctx.addVariable(check.Args.Strings[0]), false)
+		if strings.HasSuffix(check.Name, "ndef") {
 			v = &notExpr{v}
 		}
 		return &ifNode{

mk2rbc/mk2rbc_test.go

@@ -131,7 +131,7 @@ load(":part1.star|init", _part1_init = "init")
 def init(g, handle):
   cfg = rblf.cfg(handle)
   rblf.inherit(handle, "part", _part_init)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     if not _part1_init:
       rblf.mkerror("product.mk", "Cannot find %s" % (":part1.star"))
     rblf.inherit(handle, "part1", _part1_init)
@@ -174,7 +174,7 @@ load(":part1.star|init", _part1_init = "init")
 def init(g, handle):
   cfg = rblf.cfg(handle)
   _part_init(g, handle)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     if not _part1_init:
       rblf.mkerror("product.mk", "Cannot find %s" % (":part1.star"))
     _part1_init(g, handle)
@@ -231,7 +231,7 @@ endif
 
 def init(g, handle):
   cfg = rblf.cfg(handle)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     cfg["PRODUCT_NAME"] = "gizmo"
   else:
     pass
@@ -275,7 +275,7 @@ endif
 
 def init(g, handle):
   cfg = rblf.cfg(handle)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     # Comment
     pass
   else:
@@ -296,7 +296,7 @@ endif
 
 def init(g, handle):
   cfg = rblf.cfg(handle)
-  if not g.get("PRODUCT_NAME") != None:
+  if not cfg.get("PRODUCT_NAME", ""):
     cfg["PRODUCT_NAME"] = "gizmo1"
   else:
     cfg["PRODUCT_NAME"] = "gizmo2"
@@ -315,9 +315,9 @@ endif
 
 def init(g, handle):
   cfg = rblf.cfg(handle)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     cfg["PRODUCT_NAME"] = "gizmo"
-  elif not g.get("PRODUCT_PACKAGES") != None:
+  elif not cfg.get("PRODUCT_PACKAGES", []):
     # Comment
     pass
 `,
@@ -509,11 +509,11 @@ endif
 
 def init(g, handle):
   cfg = rblf.cfg(handle)
-  if g.get("PRODUCT_NAME") != None:
+  if cfg.get("PRODUCT_NAME", ""):
     cfg["PRODUCT_PACKAGES"] = ["pack-if0"]
-    if g.get("PRODUCT_MODEL") != None:
+    if cfg.get("PRODUCT_MODEL", ""):
       cfg["PRODUCT_PACKAGES"] = ["pack-if-if"]
-    elif g.get("PRODUCT_NAME") != None:
+    elif cfg.get("PRODUCT_NAME", ""):
       cfg["PRODUCT_PACKAGES"] = ["pack-if-elif"]
     else:
       cfg["PRODUCT_PACKAGES"] = ["pack-if-else"]