Handle custom completion match prefix / LCD

A following patch will add support for wild matching for C++ symbols,
making completing on "b push_ba" on a C++ program complete to
std::vector<...>::push_back, std::string::push_back etc., like:

 (gdb) b push_ba[TAB]
 std::vector<...>::push_back(....)
 std::string<...>::push_back(....)

Currently, we compute the "lowest common denominator" between all
completion candidates (what the input line is adjusted to) as the
common prefix of all matches.  That's problematic with wild matching
as above, as then we'd end up with TAB changing the input line to
"b std::", losing the original input, like:

 (gdb) b push_ba[TAB]
 std::vector<...>::push_back(....)
 std::string<...>::push_back(....)
 (gdb) b std::

while obviously we'd want it to adjust itself to "b push_back(" instead:

 (gdb) b push_ba[TAB]
 std::vector<...>::push_back(....)
 std::string<...>::push_back(....)
 (gdb) b push_back(

This patch adds the core code necessary to support this, though
nothing really makes use of it yet in this patch.

gdb/ChangeLog:
2017-11-29  Pedro Alves  <palves@redhat.com>

	* ada-lang.c (ada_lookup_name_info::matches): Change type of
	parameter from completion_match to completion_match_result.
	Adjust.
	(do_wild_match, do_full_match, ada_symbol_name_matches): Likewise.
	* completer.c (completion_tracker::maybe_add_completion): Add
	match_for_lcd parameter and use it.
	(completion_tracker::add_completion): Likewise.
	* completer.h (class completion_match_for_lcd): New class.
	(completion_match_result::match_for_lcd): New field.
	(completion_match_result::set_match): New method.
	(completion_tracker): Add comments.
	(completion_tracker::add_completion): Add match_for_lcd parameter.
	(completion_tracker::reset_completion_match_result): Reset
	match_for_lcd too.
	(completion_tracker::maybe_add_completion): Add match_for_lcd
	parameter.
	(completion_tracker::m_lowest_common_denominator_unique): Extend
	comments.
	* cp-support.c (cp_symbol_name_matches_1)
	(cp_fq_symbol_name_matches): Change type of parameter from
	completion_match to completion_match_result.  Adjust.
	* language.c (default_symbol_name_matcher): Change type of
	parameter from completion_match to completion_match_result.
	Adjust.
	* language.h (completion_match_for_lcd): Forward declare.
	(default_symbol_name_matcher): Change type of parameter from
	completion_match to completion_match_result.
	* symtab.c (compare_symbol_name): Adjust.
	(completion_list_add_name): Pass the match_for_lcd to the tracker.
	* symtab.h (ada_lookup_name_info::matches): Change type of
	parameter from completion_match to completion_match_result.
	(symbol_name_matcher_ftype): Likewise, and update comments.

1 files changed, 10 insertions, 12 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 3265c21..38d1ce6 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -6357,7 +6357,7 @@ bool
 ada_lookup_name_info::matches
   (const char *sym_name,
    symbol_name_match_type match_type,
-   completion_match *comp_match) const
+   completion_match_result *comp_match_res) const
 {
   bool match = false;
   const char *text = m_encoded_name.c_str ();
@@ -6415,15 +6415,12 @@ ada_lookup_name_info::matches
   if (!match)
     return false;
 
-  if (comp_match != NULL)
+  if (comp_match_res != NULL)
     {
-      std::string &match_str = comp_match->storage ();
+      std::string &match_str = comp_match_res->match.storage ();
 
       if (!m_encoded_p)
-	{
-	  match_str = ada_decode (sym_name);
-	  comp_match->set_match (match_str.c_str ());
-	}
+	match_str = ada_decode (sym_name);
       else
 	{
 	  if (m_verbatim_p)
@@ -6431,8 +6428,9 @@ ada_lookup_name_info::matches
 	  else
 	    match_str = sym_name;
 
-	  comp_match->set_match (match_str.c_str ());
 	}
+
+      comp_match_res->set_match (match_str.c_str ());
     }
 
   return true;
@@ -13925,7 +13923,7 @@ static const struct exp_descriptor ada_exp_descriptor = {
 static bool
 do_wild_match (const char *symbol_search_name,
 	       const lookup_name_info &lookup_name,
-	       completion_match *match)
+	       completion_match_result *comp_match_res)
 {
   return wild_match (symbol_search_name, ada_lookup_name (lookup_name));
 }
@@ -13935,7 +13933,7 @@ do_wild_match (const char *symbol_search_name,
 static bool
 do_full_match (const char *symbol_search_name,
 	       const lookup_name_info &lookup_name,
-	       completion_match *match)
+	       completion_match_result *comp_match_res)
 {
   return full_match (symbol_search_name, ada_lookup_name (lookup_name));
 }
@@ -14005,11 +14003,11 @@ ada_lookup_name_info::ada_lookup_name_info (const lookup_name_info &lookup_name)
 static bool
 ada_symbol_name_matches (const char *symbol_search_name,
 			 const lookup_name_info &lookup_name,
-			 completion_match *match)
+			 completion_match_result *comp_match_res)
 {
   return lookup_name.ada ().matches (symbol_search_name,
 				     lookup_name.match_type (),
-				     match);
+				     comp_match_res);
 }
 
 /* Implement the "la_get_symbol_name_matcher" language_defn method for