First pass at handling libpath.

Improvements, especially to platform handling, welcome.

src/core/loadbytecode.c

@@ -3,6 +3,49 @@
 /* Dummy, 0-arg callsite. */
 static MVMCallsite no_arg_callsite = { NULL, 0, 0, 0 };
 
+/* Takes a filename and prepends any --libpath value we have, if it's not an
+ * absolute path. */
+static MVMString * figure_filename(MVMThreadContext *tc, MVMString *orig) {
+    const char *lib_path = tc->instance->lib_path;
+    if (lib_path) {
+        /* We actually have a lib_path to consider. See if the filename is
+         * absolute (XXX wants a platform abstraction, and doing better). */
+        char *orig_cstr = MVM_string_utf8_encode_C_string(tc, orig);
+        int  absolute   = orig_cstr[0] == '/' || orig_cstr[0] == '\\' ||
+                          orig_cstr[1] == ':' && orig_cstr[2] == '\\';
+        if (absolute) {
+            /* Nothing more to do; we have an absolute path. */
+            free(orig_cstr);
+            return orig;
+        }
+        else {
+            /* Concatenate libpath with filename. */
+            MVMString *result;
+            size_t lib_path_len = strlen(lib_path);
+            size_t orig_len     = strlen(orig_cstr);
+            int    need_sep     = lib_path[lib_path_len - 1] != '/' &&
+                                  lib_path[lib_path_len - 1] != '\\';
+            int    new_len      = lib_path_len + (need_sep ? 1 : 0) + orig_len;
+            char * new_path     = malloc(new_len);
+            memcpy(new_path, lib_path, lib_path_len);
+            if (need_sep) {
+                new_path[lib_path_len] = '/';
+                memcpy(new_path + lib_path_len + 1, orig_cstr, orig_len);
+            }
+            else {
+                memcpy(new_path + lib_path_len, orig_cstr, orig_len);
+            }
+            result = MVM_string_utf8_decode(tc, tc->instance->VMString, new_path, new_len);
+            free(new_path);
+            return result;
+        }
+    }
+    else {
+        /* No libpath, so just hand back the original name. */
+        return orig;
+    }
+}
+
 /* Handles loading of bytecode, including triggering the deserialize and load
  * special frames. Takes place in two steps, with a callback between them which
  * is triggered by the special_return mechanism. */
@@ -11,6 +54,9 @@ void MVM_load_bytecode(MVMThreadContext *tc, MVMString *filename) {
     MVMCompUnit *cu, *try_cu;
     MVMLoadedCompUnitName *loaded_name;
 
+    /* Work out actual filename to use, taking --libpath into account. */
+    filename = figure_filename(tc, filename);
+
     /* See if we already loaded this. */
     uv_mutex_lock(&tc->instance->mutex_loaded_compunits);
     MVM_string_flatten(tc, filename);