From b8f37f4c3f8fcb2528b55143f49cb792e2de04ae Mon Sep 17 00:00:00 2001
From: Ivan Orlov <orlov@google.com>
Date: Mon, 16 Dec 2024 19:45:27 +0000
Subject: [PATCH] Document unsupported "bracket-less" collection addressing

---
 examples/README.md            | 4 ++++
 pkg/config/expression.go      | 8 ++++++++
 pkg/config/expression_test.go | 4 ++++
 3 files changed, 16 insertions(+)

diff --git a/examples/README.md b/examples/README.md
index 30883ce0f9..64364e3fd0 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -1884,6 +1884,10 @@ To learn more about how to refer to a module in a blueprint file, please consult
 Variables can be used to refer both to values defined elsewhere in the blueprint
 and to the output and structure of other modules.
 
+> [!NOTE]
+> "Brackets-less" access to elements of collection is not supported, use brackets. 
+> E.g. `pink.lime[0].salmon` instead of `pink.lime.0.salmon`.
+
 ### Blueprint expressions
 
 Expressions in a blueprint file can refer to deployment variables or the outputs
diff --git a/pkg/config/expression.go b/pkg/config/expression.go
index 3cfeb096d1..0fb75f71fd 100644
--- a/pkg/config/expression.go
+++ b/pkg/config/expression.go
@@ -88,6 +88,14 @@ func bpTraversalToTerraform(t hcl.Traversal) (hcl.Traversal, error) {
 
 // BlueprintExpressionLiteralToExpression takes  a content of `$(...)`-literal and transforms it to `Expression`
 func BlueprintExpressionLiteralToExpression(s string) (Expression, error) {
+	// TODO: FIX: this function relies on assumption that
+	// `epxrToTokens(toExpression(tokenize(X))) == tokenize(X)`
+	// This is not correct, e.g.:
+	// ```
+	// epxrToTokens(toExpression(tokenize("pink.lime.0.salmon"))) ==
+	//     tokenize("pink.lime[0].salmon") != tokenize("pink.lime.0.salmon")
+	// ```
+	// As a result `pink.lime.0.salmon` can not be properly translated.
 	bpExp, diag := hclsyntax.ParseExpression([]byte(s), "", hcl.Pos{})
 	if diag.HasErrors() {
 		return nil, diag
diff --git a/pkg/config/expression_test.go b/pkg/config/expression_test.go
index 88a8fa8338..e7a135846e 100644
--- a/pkg/config/expression_test.go
+++ b/pkg/config/expression_test.go
@@ -85,6 +85,7 @@ func TestParseBpLit(t *testing.T) {
 		{"$(vars.green.sleeve)", "var.green.sleeve", false},
 		{`$(vars.green["sleeve"])`, `var.green["sleeve"]`, false},
 		{"$(vars.green.sleeve[3])", "var.green.sleeve[3]", false},
+		{"$(vars.green[3].sleeve)", "var.green[3].sleeve", false},
 
 		{"$(var.green)", "module.var.green", false},
 		{"$(box.green)", "module.box.green", false},
@@ -135,6 +136,9 @@ echo "Hello $(vars.project_id)"
 		{"$(vars[3]])", "", true},      // can't index vars
 		{`$(vars["green"])`, "", true}, // can't index module
 
+		// TODO: uncomment
+		// see comment to `BlueprintExpressionLiteralToExpression`
+		// {"$(pink.lime.0.salmon)", "module.pink.lime[0].salmon", false},
 	}
 	for _, tc := range tests {
 		t.Run(tc.input, func(t *testing.T) {