From d28f5675b41d8d4193f1727db705aff8623a03ad Mon Sep 17 00:00:00 2001
From: Saugat Pachhai <suagatchhetri@outlook.com>
Date: Tue, 16 Feb 2021 21:06:47 +0545
Subject: [PATCH] remove support for double braces (#5476)

---
 dvc/parsing/interpolate.py     | 12 ++++++------
 tests/unit/test_interpolate.py | 13 ++-----------
 2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/dvc/parsing/interpolate.py b/dvc/parsing/interpolate.py
index 79253832f..6bb92c81a 100644
--- a/dvc/parsing/interpolate.py
+++ b/dvc/parsing/interpolate.py
@@ -22,11 +22,10 @@ RBRACK = "]"
 PERIOD = "."
 KEYCRE = re.compile(
     r"""
-    (?<!\\)                   # escape \${} or ${{}}
-    \$                        # starts with $
-    (?:({{)|({))              # either starts with double braces or single
-    (.*?)                     # match every char inside
-    (?(1)}})(?(2)})           # end with same kinds of braces it opened with
+    (?<!\\)                            # escape \${}
+    \${                                # starts with ${
+    (?P<inner>.*?)                     # match every char inside
+    }                                  # end with {
 """,
     re.VERBOSE,
 )
@@ -137,6 +136,7 @@ def parse_expr(s: str):
         result = get_parser().parseString(s, parseAll=True)
     except ParseException as exc:
         format_and_raise_parse_error(exc)
+        raise AssertionError("unreachable")
 
     joined = result.asList()
     assert len(joined) == 1
@@ -144,7 +144,7 @@ def parse_expr(s: str):
 
 
 def get_expression(match: "Match", skip_checks: bool = False):
-    _, _, inner = match.groups()
+    inner = match["inner"]
     return inner if skip_checks else parse_expr(inner)
 
 
diff --git a/tests/unit/test_interpolate.py b/tests/unit/test_interpolate.py
index e92d972d9..9e1f6d07c 100644
--- a/tests/unit/test_interpolate.py
+++ b/tests/unit/test_interpolate.py
@@ -6,13 +6,7 @@ from dvc.parsing.context import Context, recurse_not_a_node
 
 
 @pytest.mark.parametrize(
-    "template, var",
-    [
-        ("${value}", "value"),
-        ("${{item}}", "item"),
-        ("${ item }", "item"),
-        ("${{ value }}", "value"),
-    ],
+    "template, var", [("${value}", "value"), ("${ item }", "item")],
 )
 @pytest.mark.parametrize(
     "data", [True, 12, pi, None, False, 0, "0", "123", "Foobar", "", inf, 3e4]
@@ -26,10 +20,7 @@ def test_resolve_primitive_values(data, template, var):
     "template, expected",
     [
         (r"\${value}", "${value}"),
-        (r"\${{value}}", "${{value}}"),
         (r"\${ value }", "${ value }"),
-        (r"\${{ value }}", "${{ value }}"),
-        (r"\${{ value }} days", "${{ value }} days"),
         (r"\${ value } days", "${ value } days"),
         (r"Month of \${value}", "Month of ${value}"),
         (r"May the \${value} be with you", "May the ${value} be with you"),
@@ -39,7 +30,7 @@ def test_resolve_primitive_values(data, template, var):
         ),
     ],
 )
-def test_escape(template, expected, mocker):
+def test_escape(template, expected):
     context = Context({"value": "value"})
     assert context.resolve(template) == expected