[PATCH v3 2/5] gdb: prevent prefix commands from being hooks

[Marco Barisione via Gdb-patches <gdb-patches@sourceware.org>]

Currently it's possible for hooks to be prefix commands:

  define-prefix hook-run

  define hook-run
    echo Will run!\n
  end

  define hook-run subcommand
    echo Subcommand\n
  end

Then:

  (gdb) run
  Will run!
  [...]
  (gdb) hook-run subcommand
  Subcommand

This doesn't seem very useful or worse, it can be confusing.  Moreover,
this creates some obscure corner cases in a later patch adding command
renaming.

Because of this, this patch prevents hooks to become prefixes and
prefixes to become hooks.

An alternative approach would have been to prevent prefixes starting
with "hook-" or "hookpost-".  The end result would have been similar
but not identical as GDB allows commands starting with "hook-" or
"hookpost-" which are not hooks (for instance, "define
hook-this-doesnt-exist").  To be more consistent with this use case,
prefixes for commands which are named like hooks but are not hooks are
allowed.

gdb/ChangeLog:

	* cli/cli-script.c (do_define_command): Prevent prefix commands
	from becoming hooks.
	(define_prefix_command): Prevent hooks from becoming prefix
	commands.

gdb/testsuite/ChangeLog:

	* gdb.base/define-prefix.exp: Test that prefix commands cannot
	become hooks and vice versa.
---
 gdb/cli/cli-script.c                     | 25 ++++++++++++++++++------
 gdb/testsuite/gdb.base/define-prefix.exp | 24 +++++++++++++++++++++++
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index eb8853a5e64..5841f545882 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -1455,6 +1455,11 @@ do_define_command (const char *comname, int from_tty,
 	  if (!query (_("Proceed? ")))
 	    error (_("Not confirmed."));
 	}
+
+      if (c != nullptr && c->prefixlist != nullptr)
+        error (_("Command \"%s\" cannot become a hook as it's already a "
+		 "prefix command."),
+	       comfull);
     }
 
   comname = xstrdup (comname);
@@ -1592,13 +1597,21 @@ define_prefix_command (const char *comname, int from_tty)
 
   c = lookup_cmd_exact (comname, *list);
 
-  if (c != nullptr && c->theclass != class_user)
-    error (_("Command \"%s\" is built-in."), comfull);
-
-  if (c != nullptr && c->prefixlist != nullptr)
+  if (c != nullptr)
     {
-      /* c is already a user defined prefix command.  */
-      return;
+      if (c->theclass != class_user)
+        error (_("Command \"%s\" is built-in."), comfull);
+
+      if (c->prefixlist != nullptr)
+        {
+          /* C is already a user defined prefix command.  */
+          return;
+        }
+
+      if (c->hookee_pre != nullptr || c->hookee_post != nullptr)
+        error (_("Command \"%s\" cannot be a prefix command as it's "
+		 "already a hook."),
+	       comfull);
     }
 
   /* If the command does not exist at all, create it.  */
diff --git a/gdb/testsuite/gdb.base/define-prefix.exp b/gdb/testsuite/gdb.base/define-prefix.exp
index 71369caaed6..a8ce5765ec7 100644
--- a/gdb/testsuite/gdb.base/define-prefix.exp
+++ b/gdb/testsuite/gdb.base/define-prefix.exp
@@ -162,3 +162,27 @@ gdb_test "define-prefix something-not-existing something-else" \
 gdb_test "define-prefix abc-prefix something-not-existing something-else" \
     "Undefined abc-prefix command: \"something-not-existing\".*"
 
+####################
+# Check error behaviour when interacting with hooks.
+
+# Define a command and hooks into it.
+gdb_define_cmd "hookee1" {}
+gdb_define_cmd "hook-hookee1" {}
+gdb_define_cmd "hookpost-hookee1" {}
+
+# Check that making the hooks into prefix commands is not allowed.
+gdb_test_exact "define-prefix hook-hookee1" \
+  "Command \"hook-hookee1\" cannot be a prefix command as it's already a hook."
+gdb_test_exact "define-prefix hookpost-hookee1" \
+  "Command \"hookpost-hookee1\" cannot be a prefix command as it's already a hook."
+
+# Define a command and prefixes which look like hooks into it (but they
+# are not).
+gdb_define_cmd "hookee2" {}
+gdb_test_no_output "define-prefix hook-hookee2" {}
+gdb_test_no_output "define-prefix hookpost-hookee2" {}
+
+gdb_test_exact "define hook-hookee2" \
+  "Command \"hook-hookee2\" cannot become a hook as it's already a prefix command."
+gdb_test_exact "define hookpost-hookee2" \
+  "Command \"hookpost-hookee2\" cannot become a hook as it's already a prefix command."
-- 
2.28.0