commit f035d405d819078f7e2d8f2081a1a2de8685bef8
author Cole Faust <colefaust@google.com> Mon Mar 28 14:02:50 2022 -0700
committer Cole Faust <colefaust@google.com> Thu Mar 31 12:44:59 2022 -0700
tree 989cc2a4e533d6c40e5f9d0a08baec1e1d478fb6
parent 4242115d59289791600d42fbc62eade3a1b40519

Support converting simple $(eval) expressions

While supporting $(eval) in the general case is
impossible, as it would require emitting code at
runtime, it is possible to handle some special cases
that are common throughout the code base.

Specifically, an assignement expression (where the
left hand side is constant) can be converted without
needing to evaluate strings as code, as its whole
right hand side is treated as one string.

However, this eval with an assignemnt can only be
used as a statement, not an expression. So it requires
the eval to be either a top-level expression, or nested
within other expressions that can be converted to
statements such as $(foreach) or $(if).

Bug: 226974242
Test: go test
Change-Id: Ifc52ef9ab7d62a69251918fcde5463f80a98a542

mk2rbc/expr.go

diff --git a/mk2rbc/expr.go b/mk2rbc/expr.go
index dc16d1d..54bb6d1 100644
--- a/mk2rbc/expr.go
+++ b/mk2rbc/expr.go
@@ -221,11 +221,9 @@
 }
 
 func (xi *interpolateExpr) transform(transformer func(expr starlarkExpr) starlarkExpr) starlarkExpr {
-	argsCopy := make([]starlarkExpr, len(xi.args))
-	for i, arg := range xi.args {
-		argsCopy[i] = arg.transform(transformer)
+	for i := range xi.args {
+		xi.args[i] = xi.args[i].transform(transformer)
 	}
-	xi.args = argsCopy
 	if replacement := transformer(xi); replacement != nil {
 		return replacement
 	} else {
@@ -591,11 +589,9 @@
 	if cx.object != nil {
 		cx.object = cx.object.transform(transformer)
 	}
-	argsCopy := make([]starlarkExpr, len(cx.args))
-	for i, arg := range cx.args {
-		argsCopy[i] = arg.transform(transformer)
+	for i := range cx.args {
+		cx.args[i] = cx.args[i].transform(transformer)
 	}
-	cx.args = argsCopy
 	if replacement := transformer(cx); replacement != nil {
 		return replacement
 	} else {
@@ -769,3 +765,35 @@
 	x, ok := expr.(*stringLiteralExpr)
 	return ok && x.literal == ""
 }
+
+func negateExpr(expr starlarkExpr) starlarkExpr {
+	switch typedExpr := expr.(type) {
+	case *notExpr:
+		return typedExpr.expr
+	case *inExpr:
+		typedExpr.isNot = !typedExpr.isNot
+		return typedExpr
+	case *eqExpr:
+		typedExpr.isEq = !typedExpr.isEq
+		return typedExpr
+	case *binaryOpExpr:
+		switch typedExpr.op {
+		case ">":
+			typedExpr.op = "<="
+			return typedExpr
+		case "<":
+			typedExpr.op = ">="
+			return typedExpr
+		case ">=":
+			typedExpr.op = "<"
+			return typedExpr
+		case "<=":
+			typedExpr.op = ">"
+			return typedExpr
+		default:
+			return &notExpr{expr: expr}
+		}
+	default:
+		return &notExpr{expr: expr}
+	}
+}