fix: properly render double braces in f-strings. #1980

Author: nedbat

CHANGES.rst

@@ -27,12 +27,16 @@ Unreleased
   which was previously only available through the COVERAGE_CORE environment
   variable. Finishes `issue 1746`_.
 
+- Fixed incorrect rendering of f-strings with doubled braces, closing `issue
+  1980`_.
+
 - The C extension module now conforms to `PEP 489`_, closing `issue 1977`_.
   Thanks, `Adam Turner <pull 1978_>`_.
 
 .. _issue 1746: https://github.com/nedbat/coveragepy/issues/1746
 .. _issue 1977: https://github.com/nedbat/coveragepy/issues/1977
 .. _pull 1978: https://github.com/nedbat/coveragepy/pull/1978
+.. _issue 1980: https://github.com/nedbat/coveragepy/issues/1980
 .. _PEP 489: https://peps.python.org/pep-0489
 
 

coverage/env.py

@@ -147,6 +147,9 @@ class PYBEHAVIOR:
     # Some words are keywords in some places, identifiers in other places.
     soft_keywords = (PYVERSION >= (3, 10))
 
+    # f-strings are parsed as code, pep 701
+    fstring_syntax = (PYVERSION >= (3, 12))
+
     # PEP669 Low Impact Monitoring: https://peps.python.org/pep-0669/
     pep669: Final[bool] = bool(getattr(sys, "monitoring", None))
 

coverage/htmlfiles/style.scss

@@ -501,7 +501,7 @@ $border-indicator-width: .2em;
                 font-weight: bold;
                 line-height: 1px;
             }
-            .str {
+            .str, .fst {
                 color: $light-token-str;
                 @include color-dark($dark-token-str);
             }

coverage/phystokens.py

@@ -70,7 +70,7 @@ def _phys_tokens(toks: TokenInfos) -> TokenInfos:
                         # It's a multi-line string and the first line ends with
                         # a backslash, so we don't need to inject another.
                         inject_backslash = False
-                elif sys.version_info >= (3, 12) and ttype == token.FSTRING_MIDDLE:
+                elif env.PYBEHAVIOR.fstring_syntax and ttype == token.FSTRING_MIDDLE:
                     inject_backslash = False
                 if inject_backslash:
                     # Figure out what column the backslash is in.
@@ -144,6 +144,9 @@ def source_token_lines(source: str) -> TSourceTokenLines:
             elif ttype in ws_tokens:
                 mark_end = False
             else:
+                if env.PYBEHAVIOR.fstring_syntax and ttype == token.FSTRING_MIDDLE:
+                    part = part.replace("{", "{{").replace("}", "}}")
+                    ecol = scol + len(part)
                 if mark_start and scol > col:
                     line.append(("ws", " " * (scol - col)))
                     mark_start = False

tests/test_html.py

@@ -1224,6 +1224,21 @@ def test_bug_1836(self, leader: str) -> None:
             "7" + "'''",
             ]
 
+    def test_bug_1980(self) -> None:
+        self.make_file("fstring_middle.py", """\
+            x = 1
+            f'Look: {x} {{x}}!'
+            """)
+
+        cov = coverage.Coverage()
+        the_mod = self.start_import_stop(cov, "fstring_middle")
+        cov.html_report(the_mod)
+
+        assert self.get_html_report_text_lines("fstring_middle.py") == [
+            "1" + "x = 1",
+            "2" + "f'Look: {x} {{x}}!'",
+            ]
+
     def test_unicode(self) -> None:
         surrogate = "\U000e0100"
 

tests/test_phystokens.py

@@ -131,6 +131,27 @@ def test_stress(self, fname: str) -> None:
             with open(stress, encoding="utf-8") as fstress:
                 assert re.search(r"(?m) $", fstress.read()), f"{stress} needs a trailing space."
 
+    def test_fstring_middle(self) -> None:
+        tokens = list(source_token_lines(textwrap.dedent("""\
+            f'Look: {x} {{x}}!'
+            """)))
+        if env.PYBEHAVIOR.fstring_syntax:
+            assert tokens == [
+                [
+                    ("fst", "f'"),
+                    ("fst", "Look: "),
+                    ("op", "{"),
+                    ("nam", "x"),
+                    ("op", "}"),
+                    ("fst", " {{"),
+                    ("fst", "x}}"),
+                    ("fst", "!"),
+                    ("fst", "'"),
+                ],
+            ]
+        else:
+            assert tokens == [[("str", "f'Look: {x} {{x}}!'")]]
+
 
 @pytest.mark.skipif(not env.PYBEHAVIOR.soft_keywords, reason="Soft keywords are new in Python 3.10")
 class SoftKeywordTest(CoverageTest):
@@ -154,7 +175,6 @@ def match():
                 global case
             """)
         tokens = list(source_token_lines(source))
-        print(tokens)
         assert tokens[0][0] == ("key", "match")
         assert tokens[0][4] == ("nam", "match")
         assert tokens[1][1] == ("key", "case")
@@ -168,7 +188,7 @@ def match():
         assert tokens[10][2] == ("nam", "match")
         assert tokens[11][3] == ("nam", "case")
 
-    @pytest.mark.skipif(sys.version_info < (3, 12), reason="type is a soft keyword in 3.12")
+    @pytest.mark.skipif(sys.version_info < (3, 12), reason="type isn't a soft keyword until 3.12")
     def test_soft_keyword_type(self) -> None:
         source = textwrap.dedent("""\
             type Point = tuple[float, float]