w6c+selfhost: same-module preference for bare-leaf lookup

cmd/wcc/sym.c

@@ -79,6 +79,43 @@ scope_lookup_in_module(Scope *s, const char *mod, const char *name)
 	return NULL;
 }
 
+/*
+ * scope_lookup_prefer — bare-leaf lookup with same-module preference.
+ *
+ * Walks the same FNV bucket + hashnext chain + parent walk scope_lookup
+ * uses. Within each scope's bucket: Pass 1 prefers entries whose
+ * `sym.mod` matches the caller's `mod`; Pass 2 falls back to the first
+ * match regardless of mod (the existing scope_lookup semantics). We
+ * only descend to the parent scope when the current scope has no
+ * matching entry at all — so a local binding in a closer scope still
+ * shadows a same-name fn from a parent scope, even when the parent
+ * entry mod-matches.
+ *
+ * When `mod` is NULL we just call scope_lookup — there's no module
+ * identity to prefer.
+ *
+ * Used at bare-leaf lookup sites inside a known current module so that
+ * a bare `read` inside lib/os resolves to os.read rather than the
+ * io.read that happens to hash earlier into the flat scope.
+ * Qualified-lookup paths (`mod.name`) stay on scope_lookup_in_module.
+ */
+Sym *
+scope_lookup_prefer(Scope *s, const char *mod, const char *name)
+{
+	if (mod == NULL) return scope_lookup(s, name);
+	for (Scope *p = s; p; p = p->parent) {
+		u64 h = hashstr(name) % p->nbuckets;
+		Sym *fallback = NULL;
+		for (Sym *b = p->buckets[h]; b; b = b->hashnext) {
+			if (strcmp(b->name, name) != 0) continue;
+			if (b->mod && strcmp(b->mod, mod) == 0) return b;
+			if (fallback == NULL) fallback = b;
+		}
+		if (fallback) return fallback;
+	}
+	return NULL;
+}
+
 Sym *
 scope_define(Scope *s, const char *name, Skind k, Type *t, Node *decl)
 {