[PATCH v2] Raise exception if ambiguous name is used in gdb.parameter

[Hannes Domani <ssbssa@yahoo.de>]

Currently gdb.parameter doesn't raise an exception if an
ambiguous name is used, it instead returns the value of the
last partly matching parameter:
```
(gdb) show print sym
Ambiguous show print command "sym": symbol, symbol-filename, symbol-loading.
(gdb) show print symbol-loading
Printing of symbol loading messages is "full".
(gdb) py print(gdb.parameter("print sym"))
full
```

It's because lookup_cmd_composition_1 tries to detect
ambigous names by checking the return value of find_cmd
for CMD_LIST_AMBIGUOUS, which never happens, since only
lookup_cmd_1 returns CMD_LIST_AMBIGUOUS.
Instead the nfound argument contains the number of found
matches.

By using it instead, and by setting *CMD to the special value
CMD_LIST_AMBIGUOUS in this case, gdbpy_parameter can now show
the appropriate error message:
```
(gdb) py print(gdb.parameter("print sym"))
Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: Parameter `print sym' is ambiguous.
Error while executing Python code.
(gdb) py print(gdb.parameter("print symbol"))
True
(gdb) py print(gdb.parameter("print symbol-"))
Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: Parameter `print symbol-' is ambiguous.
Error while executing Python code.
(gdb) py print(gdb.parameter("print symbol-load"))
full
```

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=14639
---
v2:
- Small changes in commit message.
- Use CMD_LIST_AMBIGUOUS in lookup_cmd_composition_1 to mark
  ambiguous commands, so gdbpy_parameter can show a better
  error message.
---
 gdb/cli/cli-decode.c                      | 13 ++++++---
 gdb/python/python.c                       |  5 +++-
 gdb/testsuite/gdb.python/py-parameter.exp | 32 +++++++++++++++++++++++
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index 940cd6a2c8e..db57764578d 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -2549,7 +2549,8 @@ deprecated_cmd_warning (const char *text, struct cmd_list_element *list)
    If TEXT is a subcommand (i.e. one that is preceded by a prefix
    command) set *PREFIX_CMD.
 
-   Set *CMD to point to the command TEXT indicates.
+   Set *CMD to point to the command TEXT indicates, or to
+   CMD_LIST_AMBIGUOUS if there are multiple possible matches.
 
    If any of *ALIAS, *PREFIX_CMD, or *CMD cannot be determined or do not
    exist, they are NULL when we return.
@@ -2589,7 +2590,12 @@ lookup_cmd_composition_1 (const char *text,
       *cmd = find_cmd (command.c_str (), len, cur_list, 1, &nfound);
 
       /* We only handle the case where a single command was found.  */
-      if (*cmd == CMD_LIST_AMBIGUOUS || *cmd == nullptr)
+      if (nfound > 1)
+	{
+	  *cmd = CMD_LIST_AMBIGUOUS;
+	  return 0;
+	}
+      else if (*cmd == nullptr)
 	return 0;
       else
 	{
@@ -2623,7 +2629,8 @@ lookup_cmd_composition_1 (const char *text,
    If TEXT is a subcommand (i.e. one that is preceded by a prefix
    command) set *PREFIX_CMD.
 
-   Set *CMD to point to the command TEXT indicates.
+   Set *CMD to point to the command TEXT indicates, or to
+   CMD_LIST_AMBIGUOUS if there are multiple possible matches.
 
    If any of *ALIAS, *PREFIX_CMD, or *CMD cannot be determined or do not
    exist, they are NULL when we return.
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 951de82ef06..fa0b1ca6604 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -559,7 +559,10 @@ gdbpy_parameter (PyObject *self, PyObject *args)
       GDB_PY_HANDLE_EXCEPTION (ex);
     }
 
-  if (!found)
+  if (cmd == CMD_LIST_AMBIGUOUS)
+    return PyErr_Format (PyExc_RuntimeError,
+			 _("Parameter `%s' is ambiguous."), arg);
+  else if (!found)
     return PyErr_Format (PyExc_RuntimeError,
 			 _("Could not find parameter `%s'."), arg);
 
diff --git a/gdb/testsuite/gdb.python/py-parameter.exp b/gdb/testsuite/gdb.python/py-parameter.exp
index c1f8a80c6b7..828fe84694d 100644
--- a/gdb/testsuite/gdb.python/py-parameter.exp
+++ b/gdb/testsuite/gdb.python/py-parameter.exp
@@ -588,6 +588,37 @@ proc_with_prefix test_language {} {
     gdb_test_no_output "set lang auto"
 }
 
+proc_with_prefix test_ambiguous_parameter {} {
+    gdb_test_multiline "create parameter" \
+	"python" "" \
+	"class TestAmbiguousParam (gdb.Parameter):" "" \
+	"   def __init__ (self, name, value):" "" \
+	"      super (TestAmbiguousParam, self).__init__ (name, gdb.COMMAND_DATA, gdb.PARAM_INTEGER)" "" \
+	"      self.value = value" "" \
+	"end"
+
+    # Create parameters.
+    gdb_test "python TestAmbiguousParam('test-ambiguous-value-1', 1)" ""
+    gdb_test "python TestAmbiguousParam('test-ambiguous-value-2-extra', 2)" ""
+    gdb_test "python TestAmbiguousParam('test-ambiguous', 3)" ""
+
+    # Test unambiguous matches.
+    gdb_test "python print(gdb.parameter('test-ambiguous-value-1'))" "1"
+    gdb_test "python print(gdb.parameter('test-ambiguous-value-2-extra'))" "2"
+    gdb_test "python print(gdb.parameter('test-ambiguous-value-2'))" "2"
+    gdb_test "python print(gdb.parameter('test-ambiguous'))" "3"
+
+    # Test ambiguous names.
+    gdb_test "python print(gdb.parameter('test-ambiguou'))" \
+	"Parameter .* is ambiguous.*Error while executing Python code."
+    gdb_test "python print(gdb.parameter('test-ambiguous-'))" \
+	"Parameter .* is ambiguous.*Error while executing Python code."
+    gdb_test "python print(gdb.parameter('test-ambiguous-v'))" \
+	"Parameter .* is ambiguous.*Error while executing Python code."
+    gdb_test "python print(gdb.parameter('test-ambiguous-value-1a'))" \
+	"Could not find parameter.*Error while executing Python code."
+}
+
 test_directories
 test_data_directory
 test_boolean_parameter
@@ -600,5 +631,6 @@ test_gdb_parameter
 test_integer_parameter
 test_throwing_parameter
 test_language
+test_ambiguous_parameter
 
 rename py_param_test_maybe_no_output ""
-- 
2.35.1