debug: the `coverage debug` command no longer accepts multiple topics

3 files changed, 37 insertions, 27 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index b811114d..a95eff25 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -37,6 +37,10 @@ Unreleased
 - Debug: The `coverage debug data` command will now sniff out combinable data
   files, and report on all of them.
 
+- Debug: The `coverage debug` command used to accept a number of topics at a
+  time, and show all of them, though this was never documented.  This no longer
+  works, to allow for command-line options in the future.
+
 .. _issue 1203: https://github.com/nedbat/coveragepy/issues/1203
 
 
diff --git a/coverage/cmdline.py b/coverage/cmdline.py
index 070683b8..13783d76 100644
--- a/coverage/cmdline.py
+++ b/coverage/cmdline.py
@@ -778,31 +778,33 @@ class CoverageScript:
         if not args:
             show_help("What information would you like: config, data, sys, premain?")
             return ERR
+        if args[1:]:
+            show_help("Only one topic at a time, please")
+            return ERR
 
-        for info in args:
-            if info == 'sys':
-                sys_info = self.coverage.sys_info()
-                print(info_header("sys"))
-                for line in info_formatter(sys_info):
-                    print(f" {line}")
-            elif info == 'data':
-                print(info_header("data"))
-                data_file = self.coverage.config.data_file
-                self.do_debug_data_file(data_file)
-                for filename in combinable_files(data_file):
-                    print("-----")
-                    self.do_debug_data_file(filename)
-            elif info == 'config':
-                print(info_header("config"))
-                config_info = self.coverage.config.__dict__.items()
-                for line in info_formatter(config_info):
-                    print(f" {line}")
-            elif info == "premain":
-                print(info_header("premain"))
-                print(short_stack())
-            else:
-                show_help(f"Don't know what you mean by {info!r}")
-                return ERR
+        if args[0] == 'sys':
+            sys_info = self.coverage.sys_info()
+            print(info_header("sys"))
+            for line in info_formatter(sys_info):
+                print(f" {line}")
+        elif args[0] == 'data':
+            print(info_header("data"))
+            data_file = self.coverage.config.data_file
+            self.do_debug_data_file(data_file)
+            for filename in combinable_files(data_file):
+                print("-----")
+                self.do_debug_data_file(filename)
+        elif args[0] == 'config':
+            print(info_header("config"))
+            config_info = sorted(self.coverage.config.__dict__.items())
+            for line in info_formatter(config_info):
+                print(f" {line}")
+        elif args[0] == "premain":
+            print(info_header("premain"))
+            print(short_stack())
+        else:
+            show_help(f"Don't know what you mean by {args[0]!r}")
+            return ERR
 
         return OK
 
diff --git a/tests/test_cmdline.py b/tests/test_cmdline.py
index 112e5d68..f879461a 100644
--- a/tests/test_cmdline.py
+++ b/tests/test_cmdline.py
@@ -259,9 +259,13 @@ class CmdLineTest(BaseCmdLineTest):
             cov.save()
             """)
 
-    def test_debug(self):
-        self.cmd_help("debug", "What information would you like: config, data, sys, premain?")
-        self.cmd_help("debug foo", "Don't know what you mean by 'foo'")
+    @pytest.mark.parametrize("cmd, output", [
+        ("debug", "What information would you like: config, data, sys, premain?"),
+        ("debug foo", "Don't know what you mean by 'foo'"),
+        ("debug sys config", "Only one topic at a time, please"),
+    ])
+    def test_debug(self, cmd, output):
+        self.cmd_help(cmd, output)
 
     def test_debug_sys(self):
         self.command_line("debug sys")