Fix null termination, add ddoc

src/dmd/func.d

@@ -3621,6 +3621,12 @@ extern (C++) final class DeleteDeclaration : FuncDeclaration
     }
 }
 
+/** Show supplemental error message for a function call with mismatched arguments.
+ * Params:
+ *  loc = line information for error message
+ *  fargs = arguments to function
+ *  tf = function called
+ *  failIndex = index of first argument mismatch */
 void showArgMismatch(Loc loc, Expressions* fargs, TypeFunction tf, size_t failIndex)
 {
     if (failIndex < fargs.dim && failIndex < tf.parameters.dim)
@@ -3633,7 +3639,7 @@ void showArgMismatch(Loc loc, Expressions* fargs, TypeFunction tf, size_t failIn
         auto msg = "cannot pass %sargument `%s` of type `%s` to parameter `%s`";
         // don't print parameter type if it's already in the parameter string
         if (strcmp(par.type.toChars(), ts[1]) != 0)
-            msg ~= " of type `%s`";
+            msg ~= " of type `%s`\0";
         errorSupplemental(loc, msg.ptr,
             rv.ptr, arg.toChars(), ts[0], pc, ts[1]);
     }

src/dmd/hdrgen.d

@@ -3425,6 +3425,11 @@ extern (C++) void arrayObjectsToBuffer(OutBuffer* buf, Objects* objects)
     }
 }
 
+/** Pretty print function parameters.
+ * Params:
+ *  parameters = parameters to print, such as TypeFunction.parameters.
+ *  varargs = Kind of varargs, see TypeFunction.varargs.
+ * Returns: NT string representing parameters. */
 extern (C++) const(char)* parametersTypeToChars(Parameters* parameters, int varargs)
 {
     OutBuffer buf;
@@ -3434,6 +3439,11 @@ extern (C++) const(char)* parametersTypeToChars(Parameters* parameters, int vara
     return buf.extractString();
 }
 
+/** Pretty print function parameters.
+ * Params:
+ *  parameter = parameter to print.
+ *  varargs = Kind of varargs, see TypeFunction.varargs.
+ * Returns: NT string representing parameter. */
 extern (C++) const(char)* parameterToChars(Parameter parameter, int varargs)
 {
     OutBuffer buf;