Add a mangling for lambda-expressions (which can now appear in

unevaluated operands and therefore in function signatures).

Author: zygoloid

abi.html

@@ -5246,6 +5246,7 @@ <h4><a href="#expressions">5.1.6 Expressions</a></h4>
                  ::= L &lt;<i>nullptr</i> <a href="#mangle.type">type</a>&gt; E                                 # nullptr literal (i.e., "LDnE")
                  ::= L &lt;<i>pointer</i> <a href="#mangle.type">type</a>&gt; 0 E                               # null pointer template argument
 		 ::= L &lt;<a href="#mangle.type">type</a>&gt; &lt;<i>real-part</i> <a href="#mangle.float">float</a>&gt; _ &lt;<i>imag-part</i> <a href="#mangle.float">float</a>&gt; E   # complex floating point literal (C 2000)
+                 ::= L &lt;<i>lambda</i> <a href="#mangle.closure-type-name">closure-type-name</a>&gt; E                     # lambda expression
                  ::= L _Z &lt;<a href="#mangle.encoding">encoding</a>&gt; E                                  # external name
 
   &lt;<a name="mangle.braced-expression">braced-expression</a>&gt; ::= &lt;<a href="#mangle.expression">expression</a>&gt;
@@ -5265,6 +5266,16 @@ <h4><a href="#expressions">5.1.6 Expressions</a></h4>
 (e.g., <code>::x</code>).
 </p>
 
+<p>When a lambda expression appears in the type of a function template at namespace scope,
+that function template cannot be redeclared in other translation units,
+so this ABI does not constrain its mangling except that it cannot collide
+with symbols in other translation units.
+When a lambda expression appears in an instantiation-dependent expression
+in other contexts (for example, in the signature of a function template at class scope),
+it is mangled as a &lt;<a href="#mangle.closure-type-name">closure-type-name</a>&gt;,
+excluding any name prefix, but including its number within its context.
+The context is implied by the remaining portion of the encoding.</p>
+
 <p><code>tl</code> is used for direct-list-initializations, where the type name is directly followed by a braced-init-list; e.g., <code>MyArray{1,2,3}</code> should be mangled <code>tl7MyArrayLi1ELi2ELi3EE</code>.  If the braced-init-list is parenthesized, this is not a direct-list-initialization, and it should be mangled with <code>cv</code> and a nested <code>il</code>; for example, <code>MyArray({1,2,3})</code> should be mangled <code>cv7MyArrayilLi1ELi2ELi3EE</code>.</p>
 
 <p>If an implementation supports the full C99 designated initializer syntax (as an extension), a designator list comprising multiple designators results in