From 76d9f0984ac670fe77605ed119f47314a34a2d0d Mon Sep 17 00:00:00 2001
From: Ben Moskovitz <ben.m@buildkite.com>
Date: Fri, 21 Jun 2024 11:13:31 +1000
Subject: [PATCH] Empty escaped interpolations should just be text, not
 interpolations

---
 parser.go      | 16 ++++++++--------
 parser_test.go | 10 +++++++---
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/parser.go b/parser.go
index c69b8bf..e02cc7d 100644
--- a/parser.go
+++ b/parser.go
@@ -87,7 +87,7 @@ func (p *Parser) parseExpression(stop ...rune) (Expression, error) {
 				return nil, err
 			}
 
-			expr = append(expr, ExpressionItem{Expansion: ee})
+			expr = append(expr, ee)
 			continue
 		}
 
@@ -122,28 +122,28 @@ func (p *Parser) parseExpression(stop ...rune) (Expression, error) {
 	return expr, nil
 }
 
-func (p *Parser) parseEscapedExpansion() (Expansion, error) {
+func (p *Parser) parseEscapedExpansion() (ExpressionItem, error) {
 	next := p.peekRune()
 	switch {
 	case next == '{':
 		// if it's an escaped brace expansion, (eg $${MY_COOL_VAR:-5}) consume text until the close brace
 		id := p.scanUntil(func(r rune) bool { return r == '}' })
 		id = id + string(p.nextRune()) // we know that the next rune is a close brace, chuck it on the end
-		return EscapedExpansion{Identifier: id}, nil
+		return ExpressionItem{Expansion: EscapedExpansion{Identifier: id}}, nil
 
 	case unicode.IsLetter(next):
 		// it's an escaped identifier (eg $$MY_COOL_VAR)
 		id, err := p.scanIdentifier()
 		if err != nil {
-			return nil, err
+			return ExpressionItem{}, err
 		}
 
-		return EscapedExpansion{Identifier: id}, nil
+		return ExpressionItem{Expansion: EscapedExpansion{Identifier: id}}, nil
 
 	default:
-		// there's no identifier or brace afterward, so it's probably a literal escaped dollar sign, so return an empty identifier
-		// that will be expanded to a single dollar sign
-		return EscapedExpansion{Identifier: ""}, nil
+		// there's no identifier or brace afterward, so it's probably a literal escaped dollar sign
+		// just return a text item with the dollar sign
+		return ExpressionItem{Text: "$"}, nil
 	}
 }
 
diff --git a/parser_test.go b/parser_test.go
index a223f93..466a37a 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -174,9 +174,13 @@ func TestParser(t *testing.T) {
 		{
 			String: "this is a regex! /^start.*end$$/", // the dollar sign at the end of the regex has to be escaped to be treated as a literal dollar sign by this library
 			Expected: []interpolate.ExpressionItem{
-				{Text: "this is a regex! /^start.*end"},
-				{Expansion: interpolate.EscapedExpansion{Identifier: ""}},
-				{Text: "/"},
+				{Text: "this is a regex! /^start.*end"}, {Text: "$"}, {Text: "/"},
+			},
+		},
+		{
+			String: `this is a more different regex! /^start.*end\$/`, // the dollar sign at the end of the regex has to be escaped to be treated as a literal dollar sign by this library
+			Expected: []interpolate.ExpressionItem{
+				{Text: "this is a more different regex! /^start.*end"}, {Text: "$"}, {Text: "/"},
 			},
 		},
 	}