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<h4 class="subsection">15.4.8 Rust</h4>

<p><span class="sc">gdb</span> supports the <a href="https://www.rust-lang.org/">Rust Programming Language</a>.  Type- and value-printing, and expression
parsing, are reasonably complete.  However, there are a few
peculiarities and holes to be aware of.

     <ul>
<li>Linespecs (see <a href="Specify-Location.html#Specify-Location">Specify Location</a>) are never relative to the current
crate.  Instead, they act as if there were a global namespace of
crates, somewhat similar to the way <code>extern crate</code> behaves.

     <p>That is, if <span class="sc">gdb</span> is stopped at a breakpoint in a function in
crate &lsquo;<samp><span class="samp">A</span></samp>&rsquo;, module &lsquo;<samp><span class="samp">B</span></samp>&rsquo;, then <code>break B::f</code> will attempt
to set a breakpoint in a function named &lsquo;<samp><span class="samp">f</span></samp>&rsquo; in a crate named
&lsquo;<samp><span class="samp">B</span></samp>&rsquo;.

     <p>As a consequence of this approach, linespecs also cannot refer to
items using &lsquo;<samp><span class="samp">self::</span></samp>&rsquo; or &lsquo;<samp><span class="samp">super::</span></samp>&rsquo;.

     <li>Because <span class="sc">gdb</span> implements Rust name-lookup semantics in
expressions, it will sometimes prepend the current crate to a name. 
For example, if <span class="sc">gdb</span> is stopped at a breakpoint in the crate
&lsquo;<samp><span class="samp">K</span></samp>&rsquo;, then <code>print ::x::y</code> will try to find the symbol
&lsquo;<samp><span class="samp">K::x::y</span></samp>&rsquo;.

     <p>However, since it is useful to be able to refer to other crates when
debugging, <span class="sc">gdb</span> provides the <code>extern</code> extension to
circumvent this.  To use the extension, just put <code>extern</code> before
a path expression to refer to the otherwise unavailable &ldquo;global&rdquo;
scope.

     <p>In the above example, if you wanted to refer to the symbol &lsquo;<samp><span class="samp">y</span></samp>&rsquo; in
the crate &lsquo;<samp><span class="samp">x</span></samp>&rsquo;, you would use <code>print extern x::y</code>.

     <li>The Rust expression evaluator does not support &ldquo;statement-like&rdquo;
expressions such as <code>if</code> or <code>match</code>, or lambda expressions.

     <li>Tuple expressions are not implemented.

     <li>The Rust expression evaluator does not currently implement the
<code>Drop</code> trait.  Objects that may be created by the evaluator will
never be destroyed.

     <li><span class="sc">gdb</span> does not implement type inference for generics.  In order
to call generic functions or otherwise refer to generic items, you
will have to specify the type parameters manually.

     <li><span class="sc">gdb</span> currently uses the C<tt>++</tt> demangler for Rust.  In most
cases this does not cause any problems.  However, in an expression
context, completing a generic function name will give syntactically
invalid results.  This happens because Rust requires the &lsquo;<samp><span class="samp">::</span></samp>&rsquo;
operator between the function name and its generic arguments.  For
example, <span class="sc">gdb</span> might provide a completion like
<code>crate::f&lt;u32&gt;</code>, where the parser would require
<code>crate::f::&lt;u32&gt;</code>.

     <li>As of this writing, the Rust compiler (version 1.8) has a few holes in
the debugging information it generates.  These holes prevent certain
features from being implemented by <span class="sc">gdb</span>:
          <ul>
<li>Method calls cannot be made via traits.

          <li>Operator overloading is not implemented.

          <li>When debugging in a monomorphized function, you cannot use the generic
type names.

          <li>The type <code>Self</code> is not available.

          <li><code>use</code> statements are not available, so some names may not be
available in the crate. 
</ul>
     </ul>

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