[PATCH] fix PR c++/16117

[PATCH] fix PR c++/16117

[Tom Tromey]

This patch fixes PR c++/16117.

gdb has an extension so that users can use expressions like FILE::NAME
to choose a variable of the given name from the given file.  The bug
is that this extension takes precedence over ordinary C++ expressions
of the same form.  You might think this is merely hypothetical, but
now that C++ headers commonly do not use an extension, it is more
common.

This patch fixes the bug by making two related changes.  First, it
changes gdb to prefer the ordinary C++ meaning of a symbol over the
extended meaning.  Second, it arranges for single-quoting of the
symbol to indicate a preference for the extension.

Built and regtested on x86-64 Fedora 18.
New test case included.

2013-11-04  Tom Tromey  <tromey@redhat.com>

	PR c++/16117:
	* c-exp.y (lex_one_token): Add "is_quoted_name" argument.
	(classify_name): Likewise.  Prefer a field of "this" over a
	filename.
	(classify_inner_name, yylex): Update.

2013-11-04  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Variables): Note gdb rules for ambiguous cases.
	Add example.

2013-11-04  Tom Tromey  <tromey@redhat.com>

	* gdb.cp/includefile: New file.
	* gdb.cp/filename.exp: New file.
	* gdb.cp/filename.cc: New file.
---
 gdb/ChangeLog                     |  8 ++++++
 gdb/c-exp.y                       | 53 ++++++++++++++++++++++++++-------------
 gdb/doc/ChangeLog                 |  5 ++++
 gdb/doc/gdb.texinfo               | 22 ++++++++++++----
 gdb/testsuite/ChangeLog           |  6 +++++
 gdb/testsuite/gdb.cp/filename.cc  | 36 ++++++++++++++++++++++++++
 gdb/testsuite/gdb.cp/filename.exp | 37 +++++++++++++++++++++++++++
 gdb/testsuite/gdb.cp/includefile  | 18 +++++++++++++
 8 files changed, 162 insertions(+), 23 deletions(-)
 create mode 100644 gdb/testsuite/gdb.cp/filename.cc
 create mode 100644 gdb/testsuite/gdb.cp/filename.exp
 create mode 100644 gdb/testsuite/gdb.cp/includefile

diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index 77713dd..fecfd15 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -2415,7 +2415,7 @@ static int last_was_structop;
 /* Read one token, getting characters through lexptr.  */
 
 static int
-lex_one_token (void)
+lex_one_token (int *is_quoted_name)
 {
   int c;
   int namelen;
@@ -2425,6 +2425,7 @@ lex_one_token (void)
   char *copy;
 
   last_was_structop = 0;
+  *is_quoted_name = 0;
 
  retry:
 
@@ -2669,6 +2670,8 @@ lex_one_token (void)
 	      {
 		++tokstart;
 		namelen = lexptr - tokstart - 1;
+		*is_quoted_name = 1;
+
 		goto tryname;
 	      }
 	    else if (host_len > 1)
@@ -2813,10 +2816,11 @@ static struct obstack name_obstack;
 
 /* Classify a NAME token.  The contents of the token are in `yylval'.
    Updates yylval and returns the new token type.  BLOCK is the block
-   in which lookups start; this can be NULL to mean the global
-   scope.  */
+   in which lookups start; this can be NULL to mean the global scope.
+   IS_QUOTED_NAME is non-zero if the name token was originally quoted
+   in single quotes.  */
 static int
-classify_name (const struct block *block)
+classify_name (const struct block *block, int is_quoted_name)
 {
   struct symbol *sym;
   char *copy;
@@ -2840,16 +2844,6 @@ classify_name (const struct block *block)
     }
   else if (!sym)
     {
-      /* See if it's a file name. */
-      struct symtab *symtab;
-
-      symtab = lookup_symtab (copy);
-      if (symtab)
-	{
-	  yylval.bval = BLOCKVECTOR_BLOCK (BLOCKVECTOR (symtab), STATIC_BLOCK);
-	  return FILENAME;
-	}
-
       /* If we found a field of 'this', we might have erroneously
 	 found a constructor where we wanted a type name.  Handle this
 	 case by noticing that we found a constructor and then look up
@@ -2869,6 +2863,24 @@ classify_name (const struct block *block)
 	      return TYPENAME;
 	    }
 	}
+
+      /* If we found a field, then we want to prefer it over a
+	 filename.  However, if the name was quoted, then it is better
+	 to check for a filename or a block, since this is the only
+	 way the user has of requiring the extension to be used.  */
+      if (is_a_field_of_this.type == NULL || is_quoted_name)
+	{
+	  /* See if it's a file name. */
+	  struct symtab *symtab;
+
+	  symtab = lookup_symtab (copy);
+	  if (symtab)
+	    {
+	      yylval.bval = BLOCKVECTOR_BLOCK (BLOCKVECTOR (symtab),
+					       STATIC_BLOCK);
+	      return FILENAME;
+	    }
+	}
     }
 
   if (sym && SYMBOL_CLASS (sym) == LOC_TYPEDEF)
@@ -2938,7 +2950,7 @@ classify_inner_name (const struct block *block, struct type *context)
   char *copy;
 
   if (context == NULL)
-    return classify_name (block);
+    return classify_name (block, 0);
 
   type = check_typedef (context);
   if (TYPE_CODE (type) != TYPE_CODE_STRUCT
@@ -2986,6 +2998,7 @@ yylex (void)
   struct type *context_type = NULL;
   int last_to_examine, next_to_examine, checkpoint;
   const struct block *search_block;
+  int is_quoted_name;
 
   if (popping && !VEC_empty (token_and_value, token_fifo))
     goto do_pop;
@@ -2994,9 +3007,9 @@ yylex (void)
   /* Read the first token and decide what to do.  Most of the
      subsequent code is C++-only; but also depends on seeing a "::" or
      name-like token.  */
-  current.token = lex_one_token ();
+  current.token = lex_one_token (&is_quoted_name);
   if (current.token == NAME)
-    current.token = classify_name (expression_context_block);
+    current.token = classify_name (expression_context_block, is_quoted_name);
   if (parse_language->la_language != language_cplus
       || (current.token != TYPENAME && current.token != COLONCOLON
 	  && current.token != FILENAME))
@@ -3009,7 +3022,11 @@ yylex (void)
   last_was_coloncolon = current.token == COLONCOLON;
   while (1)
     {
-      current.token = lex_one_token ();
+      int ignore;
+
+      /* We ignore quoted names other than the very first one.
+	 Subsequent ones do not have any special meaning.  */
+      current.token = lex_one_token (&ignore);
       current.value = yylval;
       VEC_safe_push (token_and_value, token_fifo, &current);
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 28e6ff9..9737355 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -8322,11 +8322,23 @@ $4 = 0
 @end smallexample
 
 @cindex C@t{++} scope resolution
-These uses of @samp{::} are very rarely in conflict with the very similar
-use of the same notation in C@t{++}.  @value{GDBN} also supports use of the C@t{++}
-scope resolution operator in @value{GDBN} expressions.
-@c FIXME: Um, so what happens in one of those rare cases where it's in
-@c conflict??  --mew
+These uses of @samp{::} are very rarely in conflict with the very
+similar use of the same notation in C@t{++}.  When they are in
+conflict, the C@t{++} meaning takes precedence; however, this can be
+overridden by quoting the file or function name.
+
+For example, suppose the program is stopped in a method of a class
+that has a field named ``includefile'', and there is also an include
+file named ``includefile'' that defines a variable, ``some_global''.
+
+@smallexample
+(@value{GDBP}) p includefile
+$1 = 23
+(@value{GDBP}) p includefile::some_global
+A syntax error in expression, near `'.
+(@value{GDBP}) p 'includefile'::some_global
+$2 = 27
+@end smallexample
 
 @cindex wrong values
 @cindex variable values, wrong
diff --git a/gdb/testsuite/gdb.cp/filename.cc b/gdb/testsuite/gdb.cp/filename.cc
new file mode 100644
index 0000000..716f48b
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/filename.cc
@@ -0,0 +1,36 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+#include "includefile"
+
+class C {
+public:
+  int includefile[1];
+
+  C() {
+    includefile[0] = 23;
+  }
+
+  void m() {
+    /* stop here */
+  }
+};
+
+int main() {
+  C c;
+  c.m();
+}
diff --git a/gdb/testsuite/gdb.cp/filename.exp b/gdb/testsuite/gdb.cp/filename.exp
new file mode 100644
index 0000000..943cdc6
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/filename.exp
@@ -0,0 +1,37 @@
+# Copyright 2013 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/>.
+
+if { [skip_cplus_tests] } { continue }
+
+standard_testfile .cc
+
+if [get_compiler_info "c++"] {
+    return -1
+}
+
+if {[prepare_for_testing $testfile.exp $testfile $srcfile {debug c++}]} {
+    return -1
+}
+
+if ![runto_main] then {
+    perror "couldn't run to main"
+    continue
+}
+
+gdb_breakpoint [gdb_get_line_number "stop here"]
+gdb_continue_to_breakpoint "stop here"
+
+gdb_test "print includefile\[0\]" " = 23"
+gdb_test "print 'includefile'::some_global" " = 27"
diff --git a/gdb/testsuite/gdb.cp/includefile b/gdb/testsuite/gdb.cp/includefile
new file mode 100644
index 0000000..9dfa787
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/includefile
@@ -0,0 +1,18 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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 some_global = 27;
-- 
1.8.1.4

Re: [PATCH] fix PR c++/16117

[Doug Evans]

On Mon, Nov 4, 2013 at 1:16 PM, Tom Tromey <tromey@redhat.com> wrote:
> This patch fixes PR c++/16117.
>
> gdb has an extension so that users can use expressions like FILE::NAME
> to choose a variable of the given name from the given file.  The bug
> is that this extension takes precedence over ordinary C++ expressions
> of the same form.  You might think this is merely hypothetical, but
> now that C++ headers commonly do not use an extension, it is more
> common.
>
> This patch fixes the bug by making two related changes.  First, it
> changes gdb to prefer the ordinary C++ meaning of a symbol over the
> extended meaning.  Second, it arranges for single-quoting of the
> symbol to indicate a preference for the extension.

Do we need a NEWS entry for the change in behaviour?

Also, and this is just for discussion's sake,
I wonder if we'll ever need to handle nested quoting some day (blech :-)).

> [...]
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 28e6ff9..9737355 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -8322,11 +8322,23 @@ $4 = 0
>  @end smallexample
>
>  @cindex C@t{++} scope resolution
> -These uses of @samp{::} are very rarely in conflict with the very similar
> -use of the same notation in C@t{++}.  @value{GDBN} also supports use of the C@t{++}
> -scope resolution operator in @value{GDBN} expressions.
> -@c FIXME: Um, so what happens in one of those rare cases where it's in
> -@c conflict??  --mew
> +These uses of @samp{::} are very rarely in conflict with the very
> +similar use of the same notation in C@t{++}.  When they are in
> +conflict, the C@t{++} meaning takes precedence; however, this can be
> +overridden by quoting the file or function name.

Can you add text to indicate "quoting" here means single-quotes *only*?

> +For example, suppose the program is stopped in a method of a class
> +that has a field named ``includefile'', and there is also an include
> +file named ``includefile'' that defines a variable, ``some_global''.
> +
> +@smallexample
> +(@value{GDBP}) p includefile
> +$1 = 23
> +(@value{GDBP}) p includefile::some_global
> +A syntax error in expression, near `'.
> +(@value{GDBP}) p 'includefile'::some_global
> +$2 = 27
> +@end smallexample
>
>  @cindex wrong values
>  @cindex variable values, wrong
> [...]
> diff --git a/gdb/testsuite/gdb.cp/filename.exp b/gdb/testsuite/gdb.cp/filename.exp
> new file mode 100644
> index 0000000..943cdc6
> --- /dev/null
> +++ b/gdb/testsuite/gdb.cp/filename.exp
> @@ -0,0 +1,37 @@
> +# Copyright 2013 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/>.
> +
> +if { [skip_cplus_tests] } { continue }
> +
> +standard_testfile .cc
> +
> +if [get_compiler_info "c++"] {
> +    return -1
> +}
> +
> +if {[prepare_for_testing $testfile.exp $testfile $srcfile {debug c++}]} {
> +    return -1
> +}
> +
> +if ![runto_main] then {
> +    perror "couldn't run to main"
> +    continue
> +}
> +
> +gdb_breakpoint [gdb_get_line_number "stop here"]
> +gdb_continue_to_breakpoint "stop here"
> +
> +gdb_test "print includefile\[0\]" " = 23"
> +gdb_test "print 'includefile'::some_global" " = 27"

Is 'class'::member intended to work? (static member or whatever)
[It works today, but I didn't check if that's intended.  I presume it is.]
If so, maybe a test to verify that still works as well?

I grepped for "'::" in gdb.cp/*.exp and didn't find anything of use.
Since we're touching single-quote handling here, I figure this is as
good a place as any.

Re: [PATCH] fix PR c++/16117

[Tom Tromey]

>>>>> "Doug" == Doug Evans <dje@google.com> writes:

Doug> Do we need a NEWS entry for the change in behaviour?

I don't think so.

Doug> Also, and this is just for discussion's sake,
Doug> I wonder if we'll ever need to handle nested quoting some day (blech :-)).

Let's just not.

Doug> Can you add text to indicate "quoting" here means single-quotes *only*?

I'll add a link.

Doug> Is 'class'::member intended to work? (static member or whatever)
Doug> [It works today, but I didn't check if that's intended.  I presume it is.]
Doug> If so, maybe a test to verify that still works as well?

I think it's probably better to leave it undetermined.

On the one hand, I don't want to implement rejecting it.
I think that's too harsh.

On the other hand, defining it removes any flexibility in the future.

Tom

Re: [PATCH] fix PR c++/16117

[Tom Tromey]

Doug> Can you add text to indicate "quoting" here means single-quotes *only*?

Tom> I'll add a link.

Scratch that, it is in the same node.
I'll add "with single quotes" there.

Tom

Re: [PATCH] fix PR c++/16117

[Eli Zaretskii]

> From: Tom Tromey <tromey@redhat.com>
> Cc: Tom Tromey <tromey@redhat.com>
> Date: Mon,  4 Nov 2013 14:16:46 -0700
> 
> +For example, suppose the program is stopped in a method of a class
> +that has a field named ``includefile'', and there is also an include
> +file named ``includefile'' that defines a variable, ``some_global''.

All these symbols in quotes should actually use the appropriate markup
instead: @code for C++ symbols, @file for file names.

The documentation part is OK with this fixed.

> +(@value{GDBP}) p includefile::some_global
> +A syntax error in expression, near `'.

I wonder if we can do better with the pointer to the place of the
syntax error: `' is not very specific ;-)

Thanks.

Re: [PATCH] fix PR c++/16117

[Tom Tromey]

>>>>> "Eli" == Eli Zaretskii <eliz@gnu.org> writes:

>> +(@value{GDBP}) p includefile::some_global
>> +A syntax error in expression, near `'.

Eli> I wonder if we can do better with the pointer to the place of the
Eli> syntax error: `' is not very specific ;-)

It would be nice, but it's a different bug.

Tom

Re: [PATCH] fix PR c++/16117

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tromey@redhat.com> writes:

Tom> This patch fixes PR c++/16117.

I'm checking this in now.

Tom