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  <tromey@adacore.com>

	* 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  <tromey@adacore.com>

	* 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.

5 files changed, 17 insertions, 10 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index b023bfe..aa99da0 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2020-04-20  Tom Tromey  <tromey@adacore.com>
+
+	* 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  <mihails.strasuns@intel.com>
 
 	* MAINTAINERS (Write After Approval): Add myself.
diff --git a/gdb/completer.c b/gdb/completer.c
index 0dd91a7..f9631f4 100644
--- a/gdb/completer.c
+++ b/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;
 }
 
diff --git a/gdb/completer.h b/gdb/completer.h
index fd0d47b..d3afa5f 100644
--- a/gdb/completer.h
+++ b/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 ();
diff --git a/gdb/python/py-tui.c b/gdb/python/py-tui.c
index de7c396..ca88f85 100644
--- a/gdb/python/py-tui.c
+++ b/gdb/python/py-tui.c
@@ -233,7 +233,7 @@ public:
 
   ~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))
   {
   }
diff --git a/gdb/python/python.c b/gdb/python/python.c
index d65cca4..4875ffd2 100644
--- a/gdb/python/python.c
+++ b/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;