From a6152aef7ab99395413f40be7fd4f6ae9abad934 Mon Sep 17 00:00:00 2001
From: Lysandros Nikolaou <lisandrosnik@gmail.com>
Date: Tue, 4 Jul 2023 11:42:36 +0200
Subject: [PATCH 1/4] gh-106396: Special-case empty format spec to gen empty
 JoinedStr node

---
 Lib/test/test_fstring.py | 18 ++++++++++++++++++
 Parser/action_helpers.c  | 10 ++++++++++
 2 files changed, 28 insertions(+)

diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
index ba223ae124a8fb..cb14bba2602def 100644
--- a/Lib/test/test_fstring.py
+++ b/Lib/test/test_fstring.py
@@ -496,6 +496,24 @@ def test_ast_line_numbers_with_parentheses(self):
         self.assertEqual(wat2.end_col_offset, 17)
         self.assertEqual(fstring.end_col_offset, 18)
 
+    def test_ast_fstring_empty_format_spec(self):
+        expr = "f'{expr:}'"
+
+        mod = ast.parse(expr)
+        self.assertEqual(type(mod), ast.Module)
+        self.assertEqual(len(mod.body), 1)
+
+        fstring = mod.body[0].value
+        self.assertEqual(type(fstring), ast.JoinedStr)
+        self.assertEqual(len(fstring.values), 1)
+
+        fv = fstring.values[0]
+        self.assertEqual(type(fv), ast.FormattedValue)
+
+        format_spec = fv.format_spec
+        self.assertEqual(type(format_spec), ast.JoinedStr)
+        self.assertEqual(len(format_spec.values), 0)
+
     def test_docstring(self):
         def f():
             f'''Not a docstring'''
diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
index 70c267bb212fcb..7f654b78f70fc6 100644
--- a/Parser/action_helpers.c
+++ b/Parser/action_helpers.c
@@ -997,6 +997,16 @@ _PyPegen_setup_full_format_spec(Parser *p, Token *colon, asdl_expr_seq *spec, in
     if (!spec) {
         return NULL;
     }
+
+    if (asdl_seq_LEN(spec) == 1) {
+        expr_ty e = asdl_seq_GET(spec, 0);
+        if (e->kind == Constant_kind
+                && PyUnicode_Check(e->v.Constant.value)
+                && PyUnicode_GetLength(e->v.Constant.value) == 0) {
+            spec = _Py_asdl_expr_seq_new(0, arena);
+        }
+    }
+
     expr_ty res = _PyAST_JoinedStr(spec, lineno, col_offset, end_lineno, end_col_offset, p->arena);
     if (!res) {
         return NULL;

From be54786a25951d6a95c3bf8e203a47126b3cd1fe Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Tue, 4 Jul 2023 09:51:52 +0000
Subject: [PATCH 2/4] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst b/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst
new file mode 100644
index 00000000000000..020fe0044878a8
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst	
@@ -0,0 +1 @@
+When the format specification of an f-string expression is empty, the parser now generates an empty :class:`ast.JoinedStr` node for it instead of adding an empty :class:`ast.Constant`.

From e13e90c30b8d2520d931735b0d720dfe2f40e43c Mon Sep 17 00:00:00 2001
From: Lysandros Nikolaou <lisandrosnik@gmail.com>
Date: Tue, 4 Jul 2023 11:53:47 +0200
Subject: [PATCH 3/4] Improve NEWS blurb

---
 .../2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst            | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst b/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst
index 020fe0044878a8..c5767e97271d9d 100644
--- a/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst	
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-07-04-09-51-45.gh-issue-106396.DmYp7x.rst	
@@ -1 +1,3 @@
-When the format specification of an f-string expression is empty, the parser now generates an empty :class:`ast.JoinedStr` node for it instead of adding an empty :class:`ast.Constant`.
+When the format specification of an f-string expression is empty, the parser now
+generates an empty :class:`ast.JoinedStr` node for it instead of an one-element
+:class:`ast.JoinedStr` with an empty string :class:`ast.Constant`.

From 85ebc869091f14fa3901455868d7dd4a0a222eaf Mon Sep 17 00:00:00 2001
From: Lysandros Nikolaou <lisandrosnik@gmail.com>
Date: Tue, 4 Jul 2023 13:19:12 +0200
Subject: [PATCH 4/4] Add comment

---
 Parser/action_helpers.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
index 7f654b78f70fc6..36e0750220a30d 100644
--- a/Parser/action_helpers.c
+++ b/Parser/action_helpers.c
@@ -998,6 +998,8 @@ _PyPegen_setup_full_format_spec(Parser *p, Token *colon, asdl_expr_seq *spec, in
         return NULL;
     }
 
+    // This is needed to keep compatibility with 3.11, where an empty format spec is parsed
+    // as an *empty* JoinedStr node, instead of having an empty constant in it.
     if (asdl_seq_LEN(spec) == 1) {
         expr_ty e = asdl_seq_GET(spec, 0);
         if (e->kind == Constant_kind