Fix regression: expression completer and scope operator (PR gdb/22584)

I noticed this regression in the expression completer:

 "(gdb) p std::[TAB]" => "(gdb) p std::std::"

obviously we should have not completed to "std::std::".

The problem is that in the earlier big completer rework, I missed
taking into account the fact that with expressions, the completion
word point is not always at the start of the symbol name (it is with
linespecs).

The fix is to run the common prefix / LCD string (what readline uses
to expand the input line) through make_completion_match_str too.

New testcase included, exercising both TAB completion and the complete
command.

gdb/ChangeLog:
2017-12-13  Pedro Alves  <palves@redhat.com>

	* completer.c (completion_tracker::maybe_add_completion): New
	'text' and 'word' parameters.  Use make_completion_match_str.
	(completion_tracker::add_completion): New 'text' and 'word'
	parameters.  Pass down.
	(completion_tracker::recompute_lowest_common_denominator): Change
	parameter type to gdb::unique_xmalloc_ptr rval ref.  Adjust.
	* completer.h (completion_tracker::add_completion): New 'text' and
	'word' parameters.
	(completion_tracker::recompute_lowest_common_denominator): Change
	parameter type to gdb::unique_xmalloc_ptr rval ref.
	(completion_tracker::recompute_lowest_common_denominator): Change
	parameter type to gdb::unique_xmalloc_ptr rval ref.
	* symtab.c (completion_list_add_name): Pass down 'text' and 'word'
	as well.

gdb/testsuite/ChangeLog:
2017-12-13  Pedro Alves  <palves@redhat.com>

	* gdb.cp/cpcompletion.exp: Load completion-support.exp.
	("expression with namespace"): New set of tests.
	* gdb.cp/pr9594.cc (Test_NS::foo, Test_NS::bar)
	(Nested::Test_NS::qux): New.
	* lib/completion-support.exp (test_gdb_complete_cmd_multiple): Add
	defaults to 'start_quote_char' and 'end_quote_char' parameters.

1 files changed, 6 insertions, 3 deletions

diff --git a/gdb/completer.h b/gdb/completer.h
index 73c0f4c..df3c8e8 100644
--- a/gdb/completer.h
+++ b/gdb/completer.h
@@ -319,7 +319,8 @@ public:
      it is not there already.  If too many completions were already
      found, this throws an error.  */
   void add_completion (gdb::unique_xmalloc_ptr<char> name,
-		       completion_match_for_lcd *match_for_lcd = NULL);
+		       completion_match_for_lcd *match_for_lcd = NULL,
+		       const char *text = NULL, const char *word = NULL);
 
   /* Add all completions matches in LIST.  Elements are moved out of
      LIST.  */
@@ -406,7 +407,8 @@ private:
      it is not there already.  If false is returned, too many
      completions were found.  */
   bool maybe_add_completion (gdb::unique_xmalloc_ptr<char> name,
-			     completion_match_for_lcd *match_for_lcd);
+			     completion_match_for_lcd *match_for_lcd,
+			     const char *text, const char *word);
 
   /* Given a new match, recompute the lowest common denominator (LCD)
      to hand over to readline.  Normally readline computes this itself
@@ -418,7 +420,8 @@ private:
      "std::vector<..>::push_back", "std::string::push_back", etc., and
      in this case we want the lowest common denominator to be
      "push_back" instead of "std::".  */
-  void recompute_lowest_common_denominator (const char *new_match);
+  void recompute_lowest_common_denominator
+    (gdb::unique_xmalloc_ptr<char> &&new_match);
 
   /* Completion match outputs returned by the symbol name matching
      routines (see symbol_name_matcher_ftype).  These results are only