fix(go-lsp): follow a type alias declared in another file of the package

internal/cbm/cbm.h

@@ -313,6 +313,12 @@ typedef struct {
      * change of all, store_impact.h follow_variant_keys). NULL on every other
      * definition. Tail field: zero-init stays valid. */
     const char *variant_key;
+    /* Go only (#2033): the raw aliased type text of an identity alias
+     * `type A = B` ("B"). Carried to the cross-file registries so a method
+     * call on A from another file follows the alias to B's method set. NULL
+     * for a defined type `type A B` (its method set is its own) and in every
+     * other language. Tail field: zero-init stays valid. */
+    const char *alias_target;
 } CBMDefinition;
 
 /* Argument captured from a call expression */

internal/cbm/extract_defs.c

@@ -8299,6 +8299,15 @@ static void emit_class_def(CBMExtractCtx *ctx, TSNode node, const CBMLangSpec *s
         def.decl_namespace = cs_type_decl_namespace(a, node, ctx->source);
     }
     def.base_classes = extract_base_classes(a, node, ctx->source, ctx->language);
+    // Go identity alias `type A = B` (#2033): keep the aliased type text so the
+    // cross-file registries can set alias_of. A defined type `type A B` is a
+    // type_spec and never gets here with this kind.
+    if (ctx->language == CBM_LANG_GO && strcmp(kind, "type_alias") == 0) {
+        TSNode target = ts_node_child_by_field_name(node, TS_FIELD("type"));
+        if (!ts_node_is_null(target)) {
+            def.alias_target = cbm_node_text(a, target, ctx->source);
+        }
+    }
     def.decorators = extract_decorators(a, node, ctx->source, ctx->language, spec);
     def.docstring = extract_docstring(ctx, node, name);
 

internal/cbm/lsp/go_lsp.c

@@ -2705,6 +2705,27 @@ static const char **split_pipe_strings(CBMArena *a, const char *text) {
     return idx > 0 ? arr : NULL;
 }
 
+/* QN of the type an identity alias `type A = B` names, for the def-driven
+ * cross-file registries (#2033). The per-file AST scan sets alias_of only for
+ * the file it walks, so an alias declared in another file of the package
+ * reaches a call only through here. Only a bare identifier is qualified (B
+ * declared in A's package); a qualified, pointer, composite or generic target
+ * stays NULL rather than guessed. */
+static const char *go_alias_target_qn(CBMArena *arena, const char *target,
+                                      const char *def_module_qn) {
+    if (!target || !target[0] || !def_module_qn || !def_module_qn[0]) {
+        return NULL;
+    }
+    for (const unsigned char *p = (const unsigned char *)target; *p; p++) {
+        bool ident = (*p >= 'a' && *p <= 'z') || (*p >= 'A' && *p <= 'Z') ||
+                     (*p >= '0' && *p <= '9') || *p == '_' || *p >= 0x80;
+        if (!ident) {
+            return NULL;
+        }
+    }
+    return cbm_arena_sprintf(arena, "%s.%s", def_module_qn, target);
+}
+
 // Helper: parse "|"-separated "name:type" field definitions and populate a registered type.
 // Format: "Binder:Binder|Name:string|Count:int"
 // type_text is resolved relative to def_module_qn.
@@ -3273,6 +3294,7 @@ void cbm_run_go_lsp_cross(CBMArena *arena, const char *source, int source_len,
             if (rt.is_interface && d->method_names_str && d->method_names_str[0]) {
                 rt.method_names = split_pipe_strings(arena, d->method_names_str);
             }
+            rt.alias_of = go_alias_target_qn(arena, d->alias_target, def_mod);
 
             cbm_registry_add_type(&reg, rt);
 
@@ -3569,6 +3591,7 @@ CBMTypeRegistry *cbm_go_build_cross_registry(CBMArena *arena, CBMLSPDef *defs, i
             if (rt.is_interface && d->method_names_str && d->method_names_str[0]) {
                 rt.method_names = split_pipe_strings(arena, d->method_names_str);
             }
+            rt.alias_of = go_alias_target_qn(arena, d->alias_target, def_mod);
             cbm_registry_add_type(reg, rt);
             GO_NOTE_NEW_TYPES();
             if (d->field_defs && d->field_defs[0]) {

internal/cbm/lsp/go_lsp.h

@@ -102,6 +102,10 @@ typedef struct {
     /* Callable identity (#2061): signature suffix of this def's graph QN;
      * qualified_name stays the base QN. NULL = none (always, until enabled). */
     const char *sig;
+    /* Go only (#2033): raw aliased type text of `type A = B` ("B"), qualified
+     * by the registrar against def_module_qn like return_types. NULL = not an
+     * identity alias. */
+    const char *alias_target;
 } CBMLSPDef;
 
 // Parse source, build registry from defs + stdlib, run LSP.

internal/cbm/result_compact.c

@@ -279,6 +279,7 @@ static void cr_walk_def(cr_ctx_t *c, CBMDefinition *d) {
     cr_list(c, &d->extra_props);
     cr_str(c, &d->decl_namespace);
     cr_str(c, &d->variant_key);
+    cr_str(c, &d->alias_target);
 }
 
 static void cr_walk_call(cr_ctx_t *c, CBMCall *call) {

src/pipeline/lsp_surface.c

@@ -34,8 +34,10 @@
 #include "yyjson/yyjson.h"
 
 /* 3: Go defs carry their parsed result list `|`-joined in "ret" (F-G8 D1);
- * a version-2 surface holds the raw result text and must be re-extracted. */
-enum { SURFACE_CODEC_VERSION = 3 };
+ * a version-2 surface holds the raw result text and must be re-extracted.
+ * 4: Go identity aliases carry their target in "al" (#2033); a version-3
+ * surface has no alias targets and must be re-extracted. */
+enum { SURFACE_CODEC_VERSION = 4 };
 
 /* Labels the incremental name registry serves that pxc_map_label does NOT
  * carry into the CBMLSPDef set. Their (name, qn, label) triple must still
@@ -394,6 +396,7 @@ static char *surface_file_to_json(const CBMFileResult *result, CBMLanguage langu
         yyjson_mut_obj_add_bool(doc, o, "ir", d->is_rust_impl_relation);
         yyjson_mut_obj_add_bool(doc, o, "ab", d->is_abstract);
         add_str_array_or_null(doc, o, "dec", d->decorators, -1);
+        add_str_or_null(doc, o, "al", d->alias_target);
         yyjson_mut_arr_add_val(lsp, o);
     }
     yyjson_mut_obj_add_val(doc, root, "lsp", lsp);
@@ -670,6 +673,7 @@ int cbm_lsp_surface_defs_from_json(CBMArena *arena, const char *defs_json, CBMLS
         d->is_abstract = yyjson_get_bool(yyjson_obj_get(o, "ab"));
         int dec_count = 0;
         d->decorators = arena_str_array(arena, yyjson_obj_get(o, "dec"), true, &dec_count);
+        d->alias_target = arena_str_or_null(arena, yyjson_obj_get(o, "al"));
         if (!d->qualified_name || !d->short_name || !d->label) {
             /* A def the writer could not have produced: qn/sn/label are
              * unconditionally present in build_lsp_def output. Corrupt row. */

src/pipeline/pass_lsp_cross.c

@@ -715,6 +715,9 @@ static int pxc_build_lsp_def(CBMArena *arena, const CBMDefinition *src, const ch
         }
     }
     dst->lang = lang;
+    dst->alias_target = (lang == CBM_LANG_GO && src->alias_target)
+                            ? cbm_arena_strdup(arena, src->alias_target)
+                            : NULL;
     dst->decorators = NULL;
     if (src->decorators) {
         int n = 0;

src/pipeline/pipeline.c

@@ -2559,7 +2559,7 @@ static void log_result_census(const char *tag, CBMFileResult **cache, int file_c
             str_def_misc += census_len(def->route_path) + census_len(def->route_method) +
                             census_len(def->impl_trait) + census_len(def->http_base_url) +
                             census_list(def->extra_props) + census_len(def->decl_namespace) +
-                            census_len(def->variant_key);
+                            census_len(def->variant_key) + census_len(def->alias_target);
         }
         for (int c = 0; c < r->calls.count; c++) {
             const CBMCall *call = &r->calls.items[c];

tests/test_go_lsp.c

@@ -1378,6 +1378,127 @@ TEST(golsp_crossfile_aliased_field_requal) {
     PASS();
 }
 
+/* #2033: an identity alias declared in another file of the same package.
+ * `type FeatureSet = bitmap` lives in one file, `bitmap.Set` in a second, the
+ * call `reqs.Set` in a third, so none of it is in the calling file's AST and
+ * only the defs can carry the alias. A defined type (`type Defined bitmap`)
+ * must not inherit bitmap's methods. The decoy `other.Set` keeps a name-only
+ * match from passing. Both cross-file registries are checked: the per-file
+ * one and the prebuilt one shared by the parallel resolve. */
+static CBMLSPDef go_crossfile_alias_defs[] = {
+    {.qualified_name = "test.main.bitmap",
+     .short_name = "bitmap",
+     .label = "Class",
+     .def_module_qn = "test.main"},
+    {.qualified_name = "test.main.bitmap.Set",
+     .short_name = "Set",
+     .label = "Method",
+     .def_module_qn = "test.main",
+     .receiver_type = "test.main.bitmap"},
+    {.qualified_name = "test.main.FeatureSet",
+     .short_name = "FeatureSet",
+     .label = "Type",
+     .def_module_qn = "test.main",
+     .alias_target = "bitmap"},
+    {.qualified_name = "test.main.Defined",
+     .short_name = "Defined",
+     .label = "Class",
+     .def_module_qn = "test.main"},
+    {.qualified_name = "test.main.Framework",
+     .short_name = "Framework",
+     .label = "Struct",
+     .def_module_qn = "test.main"},
+    {.qualified_name = "test.main.Framework.NewFeatureSet",
+     .short_name = "NewFeatureSet",
+     .label = "Method",
+     .def_module_qn = "test.main",
+     .receiver_type = "test.main.Framework",
+     .return_types = "FeatureSet"},
+    {.qualified_name = "test.main.Framework.NewDefined",
+     .short_name = "NewDefined",
+     .label = "Method",
+     .def_module_qn = "test.main",
+     .receiver_type = "test.main.Framework",
+     .return_types = "Defined"},
+    {.qualified_name = "test.main.other",
+     .short_name = "other",
+     .label = "Struct",
+     .def_module_qn = "test.main"},
+    {.qualified_name = "test.main.other.Set",
+     .short_name = "Set",
+     .label = "Method",
+     .def_module_qn = "test.main",
+     .receiver_type = "test.main.other"},
+};
+
+static const char *go_crossfile_alias_source = "package main\n\n"
+                                               "func useAlias(f *Framework) {\n"
+                                               "\treqs := f.NewFeatureSet()\n"
+                                               "\treqs.Set(3)\n}\n\n"
+                                               "func useDefined(f *Framework) {\n"
+                                               "\td := f.NewDefined()\n"
+                                               "\td.Set(3)\n}\n";
+
+static int go_crossfile_alias_check(const CBMResolvedCallArray *out) {
+    int idx = find_resolved_arr_confident(out, "useAlias", ".Set");
+    if (idx < 0 || strcmp(out->items[idx].callee_qn, "test.main.bitmap.Set") != 0) {
+        printf("  resolved calls (%d):\n", out->count);
+        for (int i = 0; i < out->count; i++) {
+            const CBMResolvedCall *rc = &out->items[i];
+            printf("    %s -> %s [%s %.2f]\n", rc->caller_qn ? rc->caller_qn : "(null)",
+                   rc->callee_qn ? rc->callee_qn : "(null)", rc->strategy ? rc->strategy : "(null)",
+                   rc->confidence);
+        }
+    }
+    ASSERT_GTE(idx, 0);
+    ASSERT_STR_EQ(out->items[idx].callee_qn, "test.main.bitmap.Set");
+    /* Reached through alias_of, so the emitter reports it the way it reports
+     * a same-file alias today (lsp_embed_dispatch): typed, not a name guess. */
+    ASSERT_TRUE(strncmp(out->items[idx].strategy, "lsp_", 4) == 0);
+    ASSERT_TRUE(strcmp(out->items[idx].strategy, "lsp_unresolved") != 0);
+    ASSERT_TRUE(out->items[idx].confidence >= 0.9f);
+    /* A defined type has its own (empty) method set. */
+    ASSERT_EQ(find_resolved_arr_confident(out, "useDefined", "bitmap.Set"), -1);
+    return 0;
+}
+
+TEST(golsp_crossfile_type_alias_method) {
+    int n = (int)(sizeof(go_crossfile_alias_defs) / sizeof(go_crossfile_alias_defs[0]));
+    CBMArena arena;
+    cbm_arena_init(&arena);
+    CBMResolvedCallArray out = {0};
+
+    cbm_run_go_lsp_cross(&arena, go_crossfile_alias_source, (int)strlen(go_crossfile_alias_source),
+                         "test.main", go_crossfile_alias_defs, n, NULL, NULL, 0, NULL, &out);
+    if (go_crossfile_alias_check(&out) != 0) {
+        cbm_arena_destroy(&arena);
+        return 1;
+    }
+
+    cbm_arena_destroy(&arena);
+    PASS();
+}
+
+TEST(golsp_crossfile_type_alias_method_prebuilt) {
+    int n = (int)(sizeof(go_crossfile_alias_defs) / sizeof(go_crossfile_alias_defs[0]));
+    CBMArena arena;
+    cbm_arena_init(&arena);
+    CBMResolvedCallArray out = {0};
+
+    CBMTypeRegistry *reg = cbm_go_build_cross_registry(&arena, go_crossfile_alias_defs, n);
+    ASSERT_NOT_NULL(reg);
+    cbm_run_go_lsp_cross_with_registry(&arena, go_crossfile_alias_source,
+                                       (int)strlen(go_crossfile_alias_source), "test.main", reg,
+                                       NULL, NULL, 0, NULL, &out);
+    if (go_crossfile_alias_check(&out) != 0) {
+        cbm_arena_destroy(&arena);
+        return 1;
+    }
+
+    cbm_arena_destroy(&arena);
+    PASS();
+}
+
 TEST(golsp_crossfile_local_interface_single_impl) {
     const char *source =
         "package main\n\n"
@@ -1542,6 +1663,8 @@ SUITE(go_lsp) {
     RUN_TEST(golsp_crossfile_interface_dispatch);
     RUN_TEST(golsp_crossfile_interface_field_chain);
     RUN_TEST(golsp_crossfile_aliased_field_requal);
+    RUN_TEST(golsp_crossfile_type_alias_method);
+    RUN_TEST(golsp_crossfile_type_alias_method_prebuilt);
     RUN_TEST(golsp_crossfile_map_index);
     RUN_TEST(golsp_crossfile_stdlib_interface);
     RUN_TEST(golsp_crossfile_local_interface_single_impl);