Implement support for sys.path when loading modules.

sys.path is not initialized by rt_init(), that's left for platform-specific
startup code. (For example, bare metal port may have some hardcoded defaults,
and let user change sys.path directly; while port for OS with environment
feature can take path from environment). If it's not explicitly initialized,
modules will be imported only from a current directory.

py/builtinimport.c

@@ -19,6 +19,8 @@
 #include "map.h"
 #include "builtin.h"
 
+mp_obj_t sys_path;
+
 mp_obj_t mp_builtin___import__(int n_args, mp_obj_t *args) {
     /*
     printf("import:\n");
@@ -37,10 +39,43 @@ mp_obj_t mp_builtin___import__(int n_args, mp_obj_t *args) {
     }
 
     // find the file to import
-    mp_lexer_t *lex = mp_import_open_file(mod_name);
+    uint mod_name_len;
+    const byte* mod_name_p = qstr_data(mod_name, &mod_name_len);
+    mp_lexer_t *lex = NULL;
+
+    uint path_num = 0;
+    mp_obj_t *path_items;
+    if (sys_path != MP_OBJ_NULL) {
+        mp_obj_list_get(sys_path, &path_num, &path_items);
+    }
+
+    if (path_num == 0) {
+        CHECKBUF(fname, PATH_MAX);
+        CHECKBUF_APPEND(fname, mod_name_p, mod_name_len);
+        CHECKBUF_APPEND(fname, ".py", sizeof(".py") - 1);
+        CHECKBUF_APPEND_0(fname);
+        lex = mp_lexer_new_from_file(fname);
+    } else {
+        for (int i = 0; i < path_num; i++) {
+            CHECKBUF(fname, PATH_MAX);
+            uint p_len;
+            const byte *p = mp_obj_str_get_data(path_items[i], &p_len);
+            if (p_len > 0) {
+                CHECKBUF_APPEND(fname, p, p_len);
+                CHECKBUF_APPEND(fname, "/", 1);
+            }
+            CHECKBUF_APPEND(fname, mod_name_p, mod_name_len);
+            CHECKBUF_APPEND(fname, ".py", sizeof(".py") - 1);
+            CHECKBUF_APPEND_0(fname);
+            lex = mp_lexer_new_from_file(fname);
+            if (lex != NULL) {
+                break;
+            }
+        }
+    }
+
     if (lex == NULL) {
-        // TODO handle lexer error correctly
-        return mp_const_none;
+        nlr_jump(mp_obj_new_exception_msg_varg(MP_QSTR_ImportError, "ImportError: No module named '%s'", mod_name_p));
     }
     qstr source_name = mp_lexer_source_name(lex);
 

py/lexerunix.c

@@ -14,7 +14,6 @@
 mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
     int fd = open(filename, O_RDONLY);
     if (fd < 0) {
-        printf("cannot open file %s\n", filename);
         return NULL;
     }
     uint size = lseek(fd, 0, SEEK_END);

py/misc.h

@@ -90,6 +90,17 @@ void vstr_add_strn(vstr_t *vstr, const char *str, int len);
 void vstr_cut_tail(vstr_t *vstr, int len);
 void vstr_printf(vstr_t *vstr, const char *fmt, ...);
 
+/** non-dynamic size-bounded variable buffer/string *************/
+
+#define CHECKBUF(buf, max_size) char buf[max_size + 1]; uint buf##_len = max_size; char *buf##_p = buf;
+#define CHECKBUF_APPEND(buf, src, src_len) \
+        { int l = MIN(src_len, buf##_len); \
+        memcpy(buf##_p, src, l); \
+        buf##_len -= l; \
+        buf##_p += l; }
+#define CHECKBUF_APPEND_0(buf) { *buf##_p = 0; }
+#define CHECKBUF_LEN(buf) (buf##_p - buf)
+
 #ifdef va_start
 void vstr_vprintf(vstr_t *vstr, const char *fmt, va_list ap);
 #endif

py/qstrdefs.h

@@ -73,6 +73,7 @@ Q(max)
 Q(min)
 Q(next)
 Q(ord)
+Q(path)
 Q(pow)
 Q(print)
 Q(range)

py/runtime.c

@@ -168,8 +168,14 @@ void rt_init(void) {
 
 #if MICROPY_CPYTHON_COMPAT
     // Precreate sys module, so "import sys" didn't throw exceptions.
-    mp_obj_new_module(MP_QSTR_sys);
+    mp_obj_t m_sys = mp_obj_new_module(MP_QSTR_sys);
+    // Avoid warning of unused var
+    (void)m_sys;
 #endif
+    // init sys.path
+    // for efficiency, left to platform-specific startup code
+    //sys_path = mp_obj_new_list(0, NULL);
+    //rt_store_attr(m_sys, MP_QSTR_path, sys_path);
 
     mp_module_micropython_init();
 

py/runtime.h

@@ -46,3 +46,4 @@ void rt_locals_set(struct _mp_map_t *m);
 struct _mp_map_t *rt_globals_get(void);
 void rt_globals_set(struct _mp_map_t *m);
 struct _mp_map_t *rt_loaded_modules_get(void);
+extern mp_obj_t sys_path;