PR c++/5645 gcc warns that pure virtual class not explicitly initialized

["Manuel López-Ibáñez" <lopezibanez@gmail.com>]

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:ADDPATCH c++:

The patch below avoids this warning by checking for nearly emptiness.
I am not sure that this is the correct approach for 100% cases, since
I ignore all specific cases that should be warned and that shouldn't.

Bootstrapped and regression tested.

OK to commit?

Cheers,

Manuel.

2007-10-27  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>
 PR c++/5645
 * init.c (emit_mem_initializers): Don't warn if the base class is nearly empty.

testsuite/
 * g++.dg/warn/pr5645.C: New.

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Index: gcc/testsuite/g++.dg/warn/pr5645.C
===================================================================
--- gcc/testsuite/g++.dg/warn/pr5645.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/pr5645.C	(revision 0)
@@ -0,0 +1,24 @@
+// PR5645: gcc warns that pure virtual class not explicitly initialized.  
+// { dg-do compile }
+// { dg-options "-Wall -Wextra" }
+
+class a {
+public:
+  virtual int f() = 0;
+  virtual int g() = 0;
+};
+
+class b : public a {
+public:
+  b();
+  b(const b& c);
+
+protected:
+  int i;
+};
+
+b::b() {}
+
+b::b(const b& c) { // { dg-bogus "base class .class a. should be explicitly initialized in the copy constructor" }
+  i = c.i;
+}
Index: gcc/cp/init.c
===================================================================
--- gcc/cp/init.c	(revision 128976)
+++ gcc/cp/init.c	(working copy)
@@ -682,14 +682,15 @@ emit_mem_initializers (tree mem_inits)
       tree subobject = TREE_PURPOSE (mem_inits);
       tree arguments = TREE_VALUE (mem_inits);
 
       /* If these initializations are taking place in a copy
 	 constructor, the base class should probably be explicitly
-	 initialized.  */
+	 initialized unless it is nearly empty.  */
       if (extra_warnings && !arguments
 	  && DECL_COPY_CONSTRUCTOR_P (current_function_decl)
-	  && TYPE_NEEDS_CONSTRUCTING (BINFO_TYPE (subobject)))
+	  && TYPE_NEEDS_CONSTRUCTING (BINFO_TYPE (subobject))
+	  && !CLASSTYPE_NEARLY_EMPTY_P (BINFO_TYPE (subobject)))
 	warning (OPT_Wextra, "%Jbase class %q#T should be explicitly initialized in the "
 		 "copy constructor",
 		 current_function_decl, BINFO_TYPE (subobject));
 
       /* If an explicit -- but empty -- initializer list was present,