1 files changed, 50 insertions, 10 deletions

diff --git a/src/main.c b/src/main.c
index 3731eec..2797d93 100644
--- a/src/main.c
+++ b/src/main.c
@@ -5,26 +5,66 @@
 #include <string.h>
 
 static int usage(void) {
-    fputs("aup check FILE\naup build FILE -o OUT.pmod\n", stderr);
+    fputs("aup check FILE\naup build FILE -o OUT.pmod\n"
+          "A library `use name` is name.aup beside FILE or in a directory of AUP_PATH (':' separated).\n", stderr);
     return 2;
 }
 
+/* Read a whole source; NULL if it cannot be read. Longer than the limit is
+ * left for the compiler to report. */
+static char *read_source(const char *path, size_t *length) {
+    FILE *file = fopen(path, "rb");
+    if (!file) return NULL;
+    char *source = malloc(AUP_SOURCE_LIMIT + 1);
+    *length = source ? fread(source, 1, AUP_SOURCE_LIMIT + 1, file) : 0;
+    bool failed = !source || ferror(file);
+    fclose(file);
+    if (failed) { free(source); return NULL; }
+    return source;
+}
+
+typedef struct { char directory[AUP_PATH]; char *sources[16]; unsigned count; } Libraries;
+
+static bool try_library(Libraries *l, const char *directory, size_t directory_length, const char *name,
+                        const char **source, size_t *length, char path[AUP_PATH]) {
+    int written = snprintf(path, AUP_PATH, "%.*s/%s.aup", (int)directory_length, directory, name);
+    if (written < 0 || written >= AUP_PATH || l->count == sizeof(l->sources) / sizeof(*l->sources)) return false;
+    char *text = read_source(path, length);
+    if (!text) return false;
+    *source = l->sources[l->count++] = text;
+    return true;
+}
+
+/* Beside the main source first, then each directory of AUP_PATH in order. */
+static bool load_library(void *context, const char *name, const char **source, size_t *length, char path[AUP_PATH]) {
+    Libraries *l = context;
+    if (try_library(l, l->directory, strlen(l->directory), name, source, length, path)) return true;
+    for (const char *at = getenv("AUP_PATH"); at && *at;) {
+        size_t span = strcspn(at, ":");
+        if (span && try_library(l, at, span, name, source, length, path)) return true;
+        at += span + (at[span] == ':');
+    }
+    return false;
+}
+
 int main(int argc, char **argv) {
     bool build = argc == 5 && !strcmp(argv[1], "build") && !strcmp(argv[3], "-o");
     if (!build && !(argc == 3 && !strcmp(argv[1], "check"))) return usage();
     const char *path = argv[2];
-    FILE *file = fopen(path, "rb");
-    if (!file) { perror(path); return 2; }
-    static char source[AUP_SOURCE_LIMIT + 1];
-    size_t length = fread(source, 1, sizeof(source), file);
-    bool unreadable = ferror(file);
-    fclose(file);
-    if (unreadable) { fprintf(stderr, "%s: cannot read\n", path); return 2; }
+    size_t length;
+    char *source = read_source(path, &length);
+    if (!source) { perror(path); return 2; }
+    Libraries libraries = {.count = 0};
+    const char *slash = strrchr(path, '/');
+    snprintf(libraries.directory, sizeof(libraries.directory), "%.*s", slash ? (int)(slash - path) : 1, slash ? path : ".");
     unsigned char *module;
     size_t size;
     AupDiagnostic error;
-    if (!aup_compile(source, length, &module, &size, &error)) {
-        fprintf(stderr, "%s:%d:%d: %s\n", path, error.line, error.column, error.message);
+    bool compiled = aup_compile(source, length, load_library, &libraries, &module, &size, &error);
+    for (unsigned i = 0; i < libraries.count; ++i) free(libraries.sources[i]);
+    free(source);
+    if (!compiled) {
+        fprintf(stderr, "%s:%d:%d: %s\n", *error.path ? error.path : path, error.line, error.column, error.message);
         return 1;
     }
     int status = 0;