w6c+selfhost: cross-module same-leaf type disambiguation via Sym.mod

cmd/wcc/sym.c

@@ -53,18 +53,66 @@ scope_lookup(Scope *s, const char *name)
 	return NULL;
 }
 
+/*
+ * scope_lookup_in_module — module-filtered chain walk.
+ *
+ * Same FNV bucket + hashnext chain + parent walk as scope_lookup,
+ * plus a (b->mod != NULL && strcmp(b->mod, mod) == 0) filter. When
+ * `mod` is NULL we fall back to unfiltered scope_lookup semantics,
+ * so callers that don't care about disambiguation get the default.
+ *
+ * Used by resolve_typename and the cexpr N_DOT branch to pick the
+ * right same-leaf-name type when two imports each export it
+ * (`bufio.stream` vs `io.stream`).
+ */
+Sym *
+scope_lookup_in_module(Scope *s, const char *mod, const char *name)
+{
+	if (mod == NULL) return scope_lookup(s, name);
+	for (; s; s = s->parent) {
+		u64 h = hashstr(name) % s->nbuckets;
+		for (Sym *b = s->buckets[h]; b; b = b->hashnext) {
+			if (strcmp(b->name, name) != 0) continue;
+			if (b->mod && strcmp(b->mod, mod) == 0) return b;
+		}
+	}
+	return NULL;
+}
+
 Sym *
 scope_define(Scope *s, const char *name, Skind k, Type *t, Node *decl)
 {
-	if (scope_lookup_local(s, name) != NULL)
-		return NULL;
+	return scope_define_in_module(s, name, NULL, k, t, decl);
+}
+
+/*
+ * scope_define_in_module — bucket insert with per-mod dedup.
+ *
+ * Same insertion as scope_define, but the duplicate-rejection key is
+ * (name, mod) rather than name alone. This lets two imports each
+ * register their own `stream` SK_TYPE in the flat scope, and lets the
+ * primary register `stream` (mod=NULL) alongside imported `stream`s.
+ *
+ * Within a single (name, mod) pair the first registration wins; later
+ * attempts return NULL and the caller emits a duplicate-type error.
+ */
+Sym *
+scope_define_in_module(Scope *s, const char *name, const char *mod,
+    Skind k, Type *t, Node *decl)
+{
+	u64 h = hashstr(name) % s->nbuckets;
+	for (Sym *b = s->buckets[h]; b; b = b->hashnext) {
+		if (strcmp(b->name, name) != 0) continue;
+		if (b->mod == NULL && mod == NULL) return NULL;
+		if (b->mod && mod && strcmp(b->mod, mod) == 0) return NULL;
+	}
 	Sym *sy = amalloc(s->a, sizeof *sy);
 	sy->name = name;
+	sy->mod = mod;
 	sy->kind = k;
 	sy->type = t;
 	sy->decl = decl;
 	sy->scope = s;
-	u64 h = hashstr(name) % s->nbuckets;
 	sy->hashnext = s->buckets[h];
 	s->buckets[h] = sy;
 	if (s->first == NULL) s->first = sy;