[RFC] Revisit PR 16253 ("Attempt to use a type name...")

[Keith Seitz <keiths at redhat dot com>]

Last year a patch was submitted/approved/commited to eliminate
symbol_matches_domain which was causing this problem.  It was later reverted
because it introduced a (severe) performance regression.

Recap:

(gdb) list
1	enum e {A,B,C} e;
2	int main (void) { return 0; }
3
(gdb) p e
Attempt to use a type name as an expression

The parser attempts to find a symbol named "e" of VAR_DOMAIN.
This gets passed down through lookup_symbol and (eventually) into
block_lookup_symbol_primary, which iterates over the block's dictionary
of symbols:

  for (sym = dict_iter_name_first (block->dict, name, &dict_iter);
       sym != NULL;
       sym = dict_iter_name_next (name, &dict_iter))
    {
      if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
                                 SYMBOL_DOMAIN (sym), domain))
        return sym;
    }

The problem here is that we have a symbol named "e" in both STRUCT_DOMAIN
and VAR_DOMAIN, and for languages like C++, Java, and Ada, where a tag name
may be used as an implicit typedef of the type, symbol_matches_domain ignores
the difference between VAR_DOMAIN and STRUCT_DOMAIN.  As it happens, the
STRUCT_DOMAIN symbol is found first, considered a match, and that symbol is
returned to the parser, eliciting the (now dreaded) error message.

Since this bug exists specifically because we have both STRUCT and VAR_DOMAIN
symbols in a given block/CU, this patch rather simply/naively changes
block_lookup_symbol_primary so that it continues to search for an exact
domain match on the symbol if symbol_matches_domain returns a symbol
which does not exactly match the requested domain.

This "fixes" the immediate problem, but admittedly might uncover other,
related bugs.  [Paranoia?] However, it causes no regressions (functional
or performance) in the test suite.

I have also resurrected the tests from the previous submission.  However
since we can still be given a matching symbol with a different domain than
requested, we cannot say that a symbol "was not found."  The error messages
today will still be the (dreaded) "Attempt to use a type name..."  I've
updated the tests to reflect this.

ChangeLog

	PR 16253
	* block.c (block_lookup_symbol_primary): If a symbol is found
	which does not exactly match the requested domain, keep searching
	for an exact match.  Otherwise, return the previously found "best"
	symbol.

testsuite/ChangeLog

	PR 16253
	* gdb.cp/var-tag.cc: New file.
	* gdb.cp/var-tag.exp: New file.
---
 gdb/ChangeLog                    |  8 ++++
 gdb/block.c                      | 16 +++++--
 gdb/testsuite/ChangeLog          |  6 +++
 gdb/testsuite/gdb.cp/var-tag.cc  | 44 +++++++++++++++++++
 gdb/testsuite/gdb.cp/var-tag.exp | 94 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 165 insertions(+), 3 deletions(-)
 create mode 100644 gdb/testsuite/gdb.cp/var-tag.cc
 create mode 100644 gdb/testsuite/gdb.cp/var-tag.exp

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9075fcc..5a7db75 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2015-06-11  Keith Seitz  <keiths@redhat.com>
+
+	PR 16253
+	* block.c (block_lookup_symbol_primary): If a symbol is found
+	which does not exactly match the requested domain, keep searching
+	for an exact match.  Otherwise, return the previously found "best"
+	symbol.
+
 2015-06-11  Gary Benson <gbenson@redhat.com>
 
 	* nat/linux-namespaces.c (mnsh_send_message): Use pulongest.
diff --git a/gdb/block.c b/gdb/block.c
index 79a8f19..e043d61 100644
--- a/gdb/block.c
+++ b/gdb/block.c
@@ -779,23 +779,33 @@ struct symbol *
 block_lookup_symbol_primary (const struct block *block, const char *name,
 			     const domain_enum domain)
 {
-  struct symbol *sym;
+  struct symbol *sym, *other;
   struct dict_iterator dict_iter;
 
   /* Verify BLOCK is STATIC_BLOCK or GLOBAL_BLOCK.  */
   gdb_assert (BLOCK_SUPERBLOCK (block) == NULL
 	      || BLOCK_SUPERBLOCK (BLOCK_SUPERBLOCK (block)) == NULL);
 
+  other = NULL;
   for (sym = dict_iter_name_first (block->dict, name, &dict_iter);
        sym != NULL;
        sym = dict_iter_name_next (name, &dict_iter))
     {
+      if (SYMBOL_DOMAIN (sym) == domain)
+	return sym;
+
+      /* This is a bit of a hack, but symbol_matches_domain might ignore
+	 STRUCT vs VAR domain symbols.  So if a matching symbol is found, make
+	 sure there is no "better" matching symbol, i.e., one with
+	 exactly the same domain.  */
       if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
 				 SYMBOL_DOMAIN (sym), domain))
-	return sym;
+	{
+	  other = sym;
+	}
     }
 
-  return NULL;
+  return other;
 }
 
 /* See block.h.  */
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 4dbbd92..b5d9873 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2015-06-11  Keith Seitz  <keiths@redhat.com>
+
+	PR 16253
+	* gdb.cp/var-tag.cc: New file.
+	* gdb.cp/var-tag.exp: New file.
+
 2015-06-10  Walfred Tedeschi  <walfred.tedeschi@intel.com>
             Mircea Gherzan  <mircea.gherzan@intel.com>
 
diff --git a/gdb/testsuite/gdb.cp/var-tag.cc b/gdb/testsuite/gdb.cp/var-tag.cc
new file mode 100644
index 0000000..93b9caf
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/var-tag.cc
@@ -0,0 +1,44 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int global = 3;
+
+class C {
+public:
+  struct C1 {} C1;
+  enum E1 {a1, b1, c1} E1;
+  union U1 {int a1; char b1;} U1;
+
+  C () : E1 (b1) {}
+  void global (void) const {}
+  int f (void) const { global (); return 0; }
+} C;
+
+struct S {} S;
+enum E {a, b, c} E;
+union U {int a; char b;} U;
+
+class CC {} cc;
+struct SS {} ss;
+enum EE {ea, eb, ec} ee;
+union UU {int aa; char bb;} uu;
+
+int
+main (void)
+{
+  return C.f ();
+}
diff --git a/gdb/testsuite/gdb.cp/var-tag.exp b/gdb/testsuite/gdb.cp/var-tag.exp
new file mode 100644
index 0000000..3a8831f
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/var-tag.exp
@@ -0,0 +1,94 @@
+# Copyright 2014, 2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite
+
+# Test expressions in which variable names shadow tag names.
+
+if {[skip_cplus_tests]} { continue }
+
+standard_testfile .cc
+
+if {[prepare_for_testing $testfile.exp $testfile $srcfile {debug c++}]} {
+    return -1
+}
+
+proc do_global_tests {lang} {
+    set invalid_print "Attempt to use a type name as an expression"
+    set ptypefmt "type = (class|enum|union|struct) %s {.*}"
+
+    with_test_prefix $lang {
+	gdb_test_no_output "set language $lang"
+	gdb_test "ptype C" "type = class C {.*}"
+	gdb_test "print E" "= a"
+	gdb_test "ptype E" "type = enum E {.*}"
+	gdb_test "print S" "= {<No data fields>}"
+	gdb_test "ptype S" "type = struct S {.*}"
+	gdb_test "print U" "= {.*}"
+	gdb_test "ptype U" "type = union U {.*}"
+	gdb_test "print cc" "= {.*}"
+	gdb_test "ptype cc" "type = class CC {.*}"
+	gdb_test "print CC" [format $invalid_print "CC"]
+	gdb_test "ptype CC" [format $ptypefmt "CC"]
+	gdb_test "print ss" "= {<No data fields>}"
+	gdb_test "ptype ss" "type = struct SS {.*}"
+	gdb_test "print SS" [format $invalid_print "SS"]
+	gdb_test "ptype SS" [format $ptypefmt "SS"]
+	gdb_test "print ee" "= .*"
+	gdb_test "ptype ee" "type = enum EE {.*}"
+	gdb_test "print EE" [format $invalid_print "EE"]
+	gdb_test "ptype EE" [format $ptypefmt "EE"]
+	gdb_test "print uu" "= {.*}"
+	gdb_test "ptype uu" "type = union UU {.*}"
+	gdb_test "print UU" [format $invalid_print  "UU"]
+	gdb_test "ptype UU" [format $ptypefmt "UU"]
+    }
+}
+
+# First test expressions when there is no context.
+with_test_prefix "before start" {
+    do_global_tests c++
+    do_global_tests c
+}
+
+# Run to main and test again.
+if {![runto_main]} {
+    perror "couldn't run to main"
+    continue
+}
+
+with_test_prefix "in main" {
+    do_global_tests c++
+    do_global_tests c
+}
+
+# Finally run to C::f and test again
+gdb_breakpoint "C::f"
+gdb_continue_to_breakpoint "continue to C::f"
+with_test_prefix "in C::f" {
+    do_global_tests c++
+    do_global_tests c
+}
+
+# Another hard-to-guess-the-users-intent bug...
+# It would be really nice if we could query the user!
+with_test_prefix "global collision" {
+    gdb_test_no_output "set language c++"
+    setup_kfail "c++/16463" "*-*-*"
+    gdb_test "print global" "= 3"
+
+    # ... with a simple workaround:
+    gdb_test "print ::global" "= 3"
+}
-- 
2.1.0