parametrization: convert bool to string as "true"/"false"

Previously, Python's `str()` was being used that
resulted in boolean transformed into "True"/"False".

Fixes iterative#4996

dvc/parsing/interpolate.py

@@ -1,5 +1,6 @@
 import re
 import typing
+from functools import singledispatch
 
 from pyparsing import (
     CharsNotIn,
@@ -57,6 +58,16 @@ def format_and_raise_parse_error(exc):
     raise ParseError(_format_exc_msg(exc))
 
 
+@singledispatch
+def to_str(obj):
+    return str(obj)
+
+
+@to_str.register(bool)
+def _(obj: bool):
+    return "true" if obj else "false"
+
+
 def _format_exc_msg(exc: ParseException):
     exc.loc += 2  # 2 because we append `${` at the start of expr below
 
@@ -103,7 +114,7 @@ def str_interpolate(template: str, matches: "List[Match]", context: "Context"):
             raise ParseError(
                 f"Cannot interpolate data of type '{type(value).__name__}'"
             )
-        buf += template[index:start] + str(value)
+        buf += template[index:start] + to_str(value)
         index = end
     buf += template[index:]
     # regex already backtracks and avoids any `${` starting with

tests/func/test_stage_resolver.py

@@ -337,12 +337,16 @@ def test_set(tmp_dir, dvc, value):
         }
     }
     resolver = DataResolver(dvc, PathInfo(str(tmp_dir)), d)
+    if isinstance(value, bool):
+        stringified_value = "true" if value else "false"
+    else:
+        stringified_value = str(value)
     assert_stage_equal(
         resolver.resolve(),
         {
             "stages": {
                 "build": {
-                    "cmd": f"python script.py --thresh {value}",
+                    "cmd": f"python script.py --thresh {stringified_value}",
                     "always_changed": value,
                 }
             }

tests/unit/test_context.py

@@ -411,6 +411,17 @@ def test_resolve_resolves_dict_keys():
     }
 
 
+def test_resolve_resolves_boolean_value():
+    d = {"enabled": True, "disabled": False}
+    context = Context(d)
+
+    assert context.resolve_str("${enabled}") is True
+    assert context.resolve_str("${disabled}") is False
+
+    assert context.resolve_str("--flag ${enabled}") == "--flag true"
+    assert context.resolve_str("--flag ${disabled}") == "--flag false"
+
+
 def test_merge_from_raises_if_file_not_exist(tmp_dir, dvc):
     context = Context(foo="bar")
     with pytest.raises(ParamsFileNotFound):