Added support for "guard" local object naming convention

For a local variable whose name starts with "guard" we do not automatically move from last use. This gives language meaning to a naming convention of "guard" as a name prefix for guard-like stack objects, such as local `std::scoped_lock` objects, whose destructors are always the object's real last use.

Author: hsutter

docs/cpp2/functions.md

@@ -388,10 +388,12 @@ In a function body, a **definite last use** of a local name is a single use of t
 
 For each definite last use:
 
-- If the name is a local object or a `copy` or `move` parameter, we know the object will not be used again before being destroyed, and so the object is automatically treated as an rvalue (move candidate). If the expression that contains the last use is able to move from the rvalue, the move will happen automatically.
+- If the name is a `copy` or `move` parameter or is a local object whose name does not start with `guard`, we know the object will not be used again before being destroyed, and so the object is automatically treated as an rvalue (move candidate). If the expression that contains the last use is able to move from the rvalue, the move will happen automatically.
 
 - If the name is a `forward` parameter, the object is automatically forwarded to preserve its constness and value category (`std::forward`-ed).
 
+> Note: This gives language meaning to a naming convention of `guard` as a name prefix for "guard" stack objects, such as local `std::scoped_lock` objects, whose destructors are always the object's real last use.
+
 For example:
 
 ``` cpp title="Definite last uses" linenums="1" hl_lines="13 16 19 21"

regression-tests/test-results/version

@@ -1,4 +1,4 @@
 
-cppfront compiler v0.8.0 Build 9A10:1540
+cppfront compiler v0.8.0 Build 9A31:1626
 SPDX-License-Identifier  Apache-2.0 WITH LLVM-exception
 Copyright (c) 2022-2024  Herb Sutter

source/build.info

@@ -1 +1 @@
-"9A10:1540"
+"9A31:1626"

source/to_cpp1.h

@@ -1764,6 +1764,7 @@ class cppfront
         //  Otherwise we'll use cpp2::move
         bool add_move =
             !add_forward
+            && !n.identifier->as_string_view().starts_with("guard")
             && (
                 !last_use
                 || last_use->safe_to_move