Mark move constructors as "noexcept"

I recently learned that move constructors generally should be marked
"noexcept".  This ensures that standard containers will move objects
when possible, rather than copy them.

This patch fixes the cases I could find.  Note that implicitly-defined
or defaulted move constructors will automatically do what you'd
expect; that is, they are noexcept if all the members have noexcept
move constructors.

While doing this, I noticed a couple of odd cases where the move
constructor seemed to assume that the object being constructed could
have state requiring destruction.  I've fixed these as well.  See
completion_result and scoped_mmap.

gdb/ChangeLog
2020-04-20  Tom Tromey  <[email protected]>

	* python/python.c (struct gdbpy_event): Mark move constructor as
	noexcept.
	* python/py-tui.c (class gdbpy_tui_window_maker): Mark move
	constructor as noexcept.
	* completer.h (struct completion_result): Mark move constructor as
	noexcept.
	* completer.c (completion_result::completion_result): Use
	initialization style.  Don't call reset_match_list.

gdbsupport/ChangeLog
2020-04-20  Tom Tromey  <[email protected]>

	* scoped_mmap.h (scoped_mmap): Mark move constructor as noexcept.
	Use initialization style.  Don't call destroy.
	* scoped_fd.h (class scoped_fd): Mark move constructor as
	noexcept.
	* gdb_ref_ptr.h (class ref_ptr): Mark move constructor as
	noexcept.

gdb/ChangeLog

@@ -1,3 +1,14 @@
+2020-04-20  Tom Tromey  <[email protected]>
+
+	* python/python.c (struct gdbpy_event): Mark move constructor as
+	noexcept.
+	* python/py-tui.c (class gdbpy_tui_window_maker): Mark move
+	constructor as noexcept.
+	* completer.h (struct completion_result): Mark move constructor as
+	noexcept.
+	* completer.c (completion_result::completion_result): Use
+	initialization style.  Don't call reset_match_list.
+
 2020-04-20  Mihails Strasuns  <[email protected]>
 
 	* MAINTAINERS (Write After Approval): Add myself.

gdb/completer.c

@@ -2327,15 +2327,11 @@ completion_result::~completion_result ()
 
 /* See completer.h  */
 
-completion_result::completion_result (completion_result &&rhs)
+completion_result::completion_result (completion_result &&rhs) noexcept
+  : match_list (rhs.match_list),
+    number_matches (rhs.number_matches)
 {
-  if (this == &rhs)
-    return;
-
-  reset_match_list ();
-  match_list = rhs.match_list;
   rhs.match_list = NULL;
-  number_matches = rhs.number_matches;
   rhs.number_matches = 0;
 }
 

gdb/completer.h

@@ -242,7 +242,7 @@ struct completion_result
   DISABLE_COPY_AND_ASSIGN (completion_result);
 
   /* Move a result.  */
-  completion_result (completion_result &&rhs);
+  completion_result (completion_result &&rhs) noexcept;
 
   /* Release ownership of the match list array.  */
   char **release_match_list ();

gdb/python/py-tui.c

@@ -233,7 +233,7 @@ class gdbpy_tui_window_maker
 
   ~gdbpy_tui_window_maker ();
 
-  gdbpy_tui_window_maker (gdbpy_tui_window_maker &&other)
+  gdbpy_tui_window_maker (gdbpy_tui_window_maker &&other) noexcept
     : m_constr (std::move (other.m_constr))
   {
   }

gdb/python/python.c

@@ -975,7 +975,7 @@ struct gdbpy_event
   {
   }
 
-  gdbpy_event (gdbpy_event &&other)
+  gdbpy_event (gdbpy_event &&other) noexcept
     : m_func (other.m_func)
   {
     other.m_func = nullptr;

gdbsupport/ChangeLog

@@ -1,3 +1,12 @@
+2020-04-20  Tom Tromey  <[email protected]>
+
+	* scoped_mmap.h (scoped_mmap): Mark move constructor as noexcept.
+	Use initialization style.  Don't call destroy.
+	* scoped_fd.h (class scoped_fd): Mark move constructor as
+	noexcept.
+	* gdb_ref_ptr.h (class ref_ptr): Mark move constructor as
+	noexcept.
+
 2020-04-13  Tom Tromey  <[email protected]>
 
 	* event-loop.c: Move comment.  Remove obsolete 	comment.

gdbsupport/gdb_ref_ptr.h

@@ -78,7 +78,7 @@ class ref_ptr
   }
 
   /* Transfer ownership from OTHER.  */
-  ref_ptr (ref_ptr &&other)
+  ref_ptr (ref_ptr &&other) noexcept
     : m_obj (other.m_obj)
   {
     other.m_obj = NULL;

gdbsupport/scoped_fd.h

@@ -30,7 +30,7 @@ class scoped_fd
 public:
   explicit scoped_fd (int fd = -1) noexcept : m_fd (fd) {}
 
-  scoped_fd (scoped_fd &&other)
+  scoped_fd (scoped_fd &&other) noexcept
     : m_fd (other.m_fd)
   {
     other.m_fd = -1;

gdbsupport/scoped_mmap.h

@@ -42,13 +42,10 @@ class scoped_mmap
     destroy ();
   }
 
-  scoped_mmap (scoped_mmap &&rhs)
+  scoped_mmap (scoped_mmap &&rhs) noexcept
+    : m_mem (rhs.m_mem),
+      m_length (rhs.m_length)
   {
-    destroy ();
-
-    m_mem = rhs.m_mem;
-    m_length = rhs.m_length;
-
     rhs.m_mem = MAP_FAILED;
     rhs.m_length = 0;
   }