[gdb/c++] Print destructor the same for gcc and clang

Consider the test-case contained in this patch.

With g++ (7.5.0) we have for "ptype A":
...
type = class A {
  public:
    int a;

    A(void);
    ~A();
}
...
and with clang++ (13.0.1):
...
type = class A {
  public:
    int a;

    A(void);
    ~A(void);
}
...
and we observe that the destructor is printed differently.

There's a difference in debug info between the two cases: in the clang case,
there's one artificial parameter, but in the g++ case, there are two, and
these similar cases are handled differently in cp_type_print_method_args.

This is due to this slightly convoluted bit of code:
...
  i = staticp ? 0 : 1;
  if (nargs > i)
    {
      while (i < nargs)
        ...
    }
  else if (varargs)
    gdb_printf (stream, "...");
  else if (language == language_cplus)
    gdb_printf (stream, "void");
...

The purpose of "i = staticp ? 0 : 1" is to skip the printing of the implicit
this parameter.

In commit 5f4d108508 ("c++/8218: Destructors w/arguments"), skipping of other
artificial parameters was added, but using a different method: rather than
adjusting the potential loop start, it skips the parameter in the loop.

The observed difference in printing is explained by whether we enter the loop:
- in the clang case, the loop is not entered and we print "void".
- in the gcc case, the loop is entered, and nothing is printed.

Fix this by rewriting the code to:
- always enter the loop
- handle whether arguments need printing in the loop
- keep track of how many arguments are printed, and
  use that after the loop to print void etc.
such that we have the same for both gcc and clang:
...
    A(void);
    ~A(void);
...

Note that I consider the discussion of whether we want to print:
- A(void) / ~A(void), or
- A() / ~A()
out-of-scope for this patch.

Tested on x86_64-linux.

gdb/c-typeprint.c

@@ -273,35 +273,44 @@ cp_type_print_method_args (struct type *mtype, const char *prefix,
 		  language_cplus, DMGL_ANSI);
   gdb_puts ("(", stream);
 
-  /* Skip the class variable.  We keep this here to accommodate older
-     compilers and debug formats which may not support artificial
-     parameters.  */
-  i = staticp ? 0 : 1;
-  if (nargs > i)
+  int printed_args = 0;
+  for (i = 0; i < nargs; ++i)
     {
-      while (i < nargs)
+      if (i == 0 && !staticp)
 	{
-	  struct field arg = args[i++];
-
-	  /* Skip any artificial arguments.  */
-	  if (FIELD_ARTIFICIAL (arg))
-	    continue;
-
-	  c_print_type (arg.type (), "", stream, 0, 0, language, flags);
-
-	  if (i == nargs && varargs)
-	    gdb_printf (stream, ", ...");
-	  else if (i < nargs)
-	    {
-	      gdb_printf (stream, ", ");
-	      stream->wrap_here (8);
-	    }
+	  /* Skip the class variable.  We keep this here to accommodate older
+	     compilers and debug formats which may not support artificial
+	     parameters.  */
+	  continue;
 	}
+
+      struct field arg = args[i];
+      /* Skip any artificial arguments.  */
+      if (FIELD_ARTIFICIAL (arg))
+	continue;
+
+      if (printed_args > 0)
+	{
+	  gdb_printf (stream, ", ");
+	  stream->wrap_here (8);
+	}
+
+      c_print_type (arg.type (), "", stream, 0, 0, language, flags);
+      printed_args++;
+    }
+
+  if (varargs)
+    {
+      if (printed_args == 0)
+	gdb_printf (stream, "...");
+      else
+	gdb_printf (stream, ", ...");
+    }
+  else if (printed_args == 0)
+    {
+      if (language == language_cplus)
+	gdb_printf (stream, "void");
     }
-  else if (varargs)
-    gdb_printf (stream, "...");
-  else if (language == language_cplus)
-    gdb_printf (stream, "void");
 
   gdb_printf (stream, ")");
 

gdb/testsuite/gdb.base/ptype-offsets.exp

@@ -104,7 +104,7 @@ gdb_test "ptype /oTM struct abc" \
 "/*     48      |       2 */    my_int_type field9;" \
 "" \
 "                               abc(void);" \
-"                               ~abc();" \
+"                               ~abc(void);" \
 "" \
 "                               typedef short my_int_type;" \
 "/* XXX  6-byte padding   */" \

gdb/testsuite/gdb.cp/print-method-args.cc

@@ -0,0 +1,38 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+class A {
+public:
+  int a;
+
+  A() {
+    this->a = 3;
+  }
+  ~A() {
+    a = 0;
+  }
+};
+
+int
+main (void)
+{
+  A a;
+
+  return a.a;
+}

gdb/testsuite/gdb.cp/print-method-args.exp

@@ -0,0 +1,38 @@
+# Copyright (C) 2022 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.
+
+# This test checks that a constructor and destructor are printed the same.
+
+if { [skip_cplus_tests] } { continue }
+
+standard_testfile .cc
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug c++}]} {
+    return -1
+}
+
+set re \
+    [multi_line \
+	 "type = class A {" \
+	 "  public:" \
+	 "    int a;" \
+	 "" \
+	 "    A\\(void\\);" \
+	 "    ~A\\(void\\);" \
+	 "}"]
+
+gdb_test "ptype A" $re

gdb/testsuite/gdb.cp/templates.exp

@@ -68,7 +68,7 @@ proc test_ptype_of_templates {} {
 	    # The destructor has an argument type.
 	    kfail "gdb/8218" "ptype T5<int>"
 	}
-	-re "type = class T5<int> \{${ws}public:${ws}static int X;${ws}int x;${ws}int val;${ws}T5\\(int\\);${ws}T5\\((T5<int> const|const T5<int>) ?&\\);${ws}~T5\\(\\);${ws}static void \\* operator new\\((size_t|unsigned( int| long|))\\);${ws}static void operator delete\\(void ?\\*\\);${ws}int value\\((void|)\\);${ws}\}\r\n$gdb_prompt $" {
+	-re "type = class T5<int> \{${ws}public:${ws}static int X;${ws}int x;${ws}int val;${ws}T5\\(int\\);${ws}T5\\((T5<int> const|const T5<int>) ?&\\);${ws}~T5\\(void\\);${ws}static void \\* operator new\\((size_t|unsigned( int| long|))\\);${ws}static void operator delete\\(void ?\\*\\);${ws}int value\\((void|)\\);${ws}\}\r\n$gdb_prompt $" {
 	    pass "ptype T5<int>"
 	}
     }
@@ -108,7 +108,7 @@ proc test_ptype_of_templates {} {
 	    # The destructor has an argument type.
 	    kfail "gdb/8218" "ptype t5i"
 	}
-	-re "type = class T5<int> \{${ws}public:${ws}static int X;${ws}int x;${ws}int val;${ws}T5\\(int\\);${ws}T5\\((T5<int> const|const T5<int>) ?&\\);${ws}~T5\\(\\);${ws}static void \\* operator new\\((size_t|unsigned( int| long|))\\);${ws}static void operator delete\\(void ?\\*\\);${ws}int value\\((void|)\\);${ws}\}\r\n$gdb_prompt $" {
+	-re "type = class T5<int> \{${ws}public:${ws}static int X;${ws}int x;${ws}int val;${ws}T5\\(int\\);${ws}T5\\((T5<int> const|const T5<int>) ?&\\);${ws}~T5\\(void\\);${ws}static void \\* operator new\\((size_t|unsigned( int| long|))\\);${ws}static void operator delete\\(void ?\\*\\);${ws}int value\\((void|)\\);${ws}\}\r\n$gdb_prompt $" {
 	    pass "ptype t5i"
 	}
     }