gh-109375: Fix bug where pdb registers an alias without an associated command (#109376)

Lib/pdb.py

@@ -1753,8 +1753,11 @@ class Pdb(bdb.Bdb, cmd.Cmd):
             for alias in keys:
                 self.message("%s = %s" % (alias, self.aliases[alias]))
             return
-        if args[0] in self.aliases and len(args) == 1:
+        if len(args) == 1:
-            self.message("%s = %s" % (args[0], self.aliases[args[0]]))
+            if args[0] in self.aliases:
+                self.message("%s = %s" % (args[0], self.aliases[args[0]]))
+            else:
+                self.error(f"Unknown alias '{args[0]}'")
         else:
             self.aliases[args[0]] = ' '.join(args[1:])
 

Lib/test/test_pdb.py

@@ -664,8 +664,10 @@ def test_pdb_alias_command():
     ...     o.method()
 
     >>> with PdbTestInput([  # doctest: +ELLIPSIS
+    ...     'alias pi',
     ...     'alias pi for k in %1.__dict__.keys(): print(f"%1.{k} = {%1.__dict__[k]}")',
     ...     'alias ps pi self',
+    ...     'alias ps',
     ...     'pi o',
     ...     's',
     ...     'ps',
@@ -674,8 +676,12 @@ def test_pdb_alias_command():
     ...    test_function()
     > <doctest test.test_pdb.test_pdb_alias_command[1]>(4)test_function()
     -> o.method()
+    (Pdb) alias pi
+    *** Unknown alias 'pi'
     (Pdb) alias pi for k in %1.__dict__.keys(): print(f"%1.{k} = {%1.__dict__[k]}")
     (Pdb) alias ps pi self
+    (Pdb) alias ps
+    ps = pi self
     (Pdb) pi o
     o.attr1 = 10
     o.attr2 = str

Misc/ACKS

@@ -254,6 +254,7 @@ Curtis Bucher
 Colm Buckley
 Erik de Bueger
 Jan-Hein Bührman
+Marc Bürg
 Lars Buitinck
 Artem Bulgakov
 Dick Bulterman

Misc/NEWS.d/next/Library/2023-09-13-17-22-44.gh-issue-109375.ijJHZ9.rst

@@ -0,0 +1 @@
+The :mod:`pdb` ``alias`` command now prevents registering aliases without arguments.