Fix #8255: py domain: number in defarg is changed to decimal

Number literals in default argument value is converted to decimal form
unexpectedly by AST module.  This fixes the signature parsing code to
recosntruct it correctly.

Note: This is only available in Python 3.8+.

3 files changed, 28 insertions, 12 deletions

diff --git a/CHANGES b/CHANGES
index 600efc466..c907992dc 100644
--- a/CHANGES
+++ b/CHANGES
@@ -49,6 +49,8 @@ Bugs fixed
 * #8277: sphinx-build: missing and redundant spacing (and etc) for console
   output on building
 * #7973: imgconverter: Check availability of imagemagick many times
+* #8255: py domain: number in default argument value is changed from hexadecimal
+  to decimal
 * #8093: The highlight warning has wrong location in some builders (LaTeX,
   singlehtml and so on)
 * #8239: Failed to refer a token in productionlist if it is indented
diff --git a/sphinx/util/inspect.py b/sphinx/util/inspect.py
index 378174993..f2cd8070b 100644
--- a/sphinx/util/inspect.py
+++ b/sphinx/util/inspect.py
@@ -600,13 +600,14 @@ def stringify_signature(sig: inspect.Signature, show_annotation: bool = True,
 
 def signature_from_str(signature: str) -> inspect.Signature:
     """Create a Signature object from string."""
-    module = ast.parse('def func' + signature + ': pass')
+    code = 'def func' + signature + ': pass'
+    module = ast.parse(code)
     function = cast(ast.FunctionDef, module.body[0])  # type: ignore
 
-    return signature_from_ast(function)
+    return signature_from_ast(function, code)
 
 
-def signature_from_ast(node: ast.FunctionDef) -> inspect.Signature:
+def signature_from_ast(node: ast.FunctionDef, code: str = '') -> inspect.Signature:
     """Create a Signature object from AST *node*."""
     args = node.args
     defaults = list(args.defaults)
@@ -626,9 +627,9 @@ def signature_from_ast(node: ast.FunctionDef) -> inspect.Signature:
             if defaults[i] is Parameter.empty:
                 default = Parameter.empty
             else:
-                default = ast_unparse(defaults[i])
+                default = ast_unparse(defaults[i], code)
 
-            annotation = ast_unparse(arg.annotation) or Parameter.empty
+            annotation = ast_unparse(arg.annotation, code) or Parameter.empty
             params.append(Parameter(arg.arg, Parameter.POSITIONAL_ONLY,
                                     default=default, annotation=annotation))
 
@@ -636,29 +637,29 @@ def signature_from_ast(node: ast.FunctionDef) -> inspect.Signature:
         if defaults[i + posonlyargs] is Parameter.empty:
             default = Parameter.empty
         else:
-            default = ast_unparse(defaults[i + posonlyargs])
+            default = ast_unparse(defaults[i + posonlyargs], code)
 
-        annotation = ast_unparse(arg.annotation) or Parameter.empty
+        annotation = ast_unparse(arg.annotation, code) or Parameter.empty
         params.append(Parameter(arg.arg, Parameter.POSITIONAL_OR_KEYWORD,
                                 default=default, annotation=annotation))
 
     if args.vararg:
-        annotation = ast_unparse(args.vararg.annotation) or Parameter.empty
+        annotation = ast_unparse(args.vararg.annotation, code) or Parameter.empty
         params.append(Parameter(args.vararg.arg, Parameter.VAR_POSITIONAL,
                                 annotation=annotation))
 
     for i, arg in enumerate(args.kwonlyargs):
-        default = ast_unparse(args.kw_defaults[i]) or Parameter.empty
-        annotation = ast_unparse(arg.annotation) or Parameter.empty
+        default = ast_unparse(args.kw_defaults[i], code) or Parameter.empty
+        annotation = ast_unparse(arg.annotation, code) or Parameter.empty
         params.append(Parameter(arg.arg, Parameter.KEYWORD_ONLY, default=default,
                                 annotation=annotation))
 
     if args.kwarg:
-        annotation = ast_unparse(args.kwarg.annotation) or Parameter.empty
+        annotation = ast_unparse(args.kwarg.annotation, code) or Parameter.empty
         params.append(Parameter(args.kwarg.arg, Parameter.VAR_KEYWORD,
                                 annotation=annotation))
 
-    return_annotation = ast_unparse(node.returns) or Parameter.empty
+    return_annotation = ast_unparse(node.returns, code) or Parameter.empty
 
     return inspect.Signature(params, return_annotation=return_annotation)
 
diff --git a/tests/test_domain_py.py b/tests/test_domain_py.py
index b98f37912..8040af9cc 100644
--- a/tests/test_domain_py.py
+++ b/tests/test_domain_py.py
@@ -386,6 +386,19 @@ def test_pyfunction_signature_full_py38(app):
                                       [desc_parameter, desc_sig_operator, "/"])])
 
 
+@pytest.mark.skipif(sys.version_info < (3, 8), reason='python 3.8+ is required.')
+def test_pyfunction_with_number_literals(app):
+    text = ".. py:function:: hello(age=0x10, height=1_6_0)"
+    doctree = restructuredtext.parse(app, text)
+    assert_node(doctree[1][0][1],
+                [desc_parameterlist, ([desc_parameter, ([desc_sig_name, "age"],
+                                                        [desc_sig_operator, "="],
+                                                        [nodes.inline, "0x10"])],
+                                      [desc_parameter, ([desc_sig_name, "height"],
+                                                        [desc_sig_operator, "="],
+                                                        [nodes.inline, "1_6_0"])])])
+
+
 def test_optional_pyfunction_signature(app):
     text = ".. py:function:: compile(source [, filename [, symbol]]) -> ast object"
     doctree = restructuredtext.parse(app, text)