Clean up and improve patterns

2 files changed, 52 insertions, 12 deletions

diff --git a/src/compile.c b/src/compile.c
index 2cc20f39..43b9ef1e 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -4200,8 +4200,12 @@ CORD compile_top_level_code(env_t *env, ast_t *ast)
     case Extend: {
         auto extend = Match(ast, Extend);
         env_t *ns_env = namespace_env(env, extend->name);
-        ns_env->libname = env->libname;
-        return compile_top_level_code(ns_env, extend->body);
+        env_t *extended = new(env_t);
+        *extended = *ns_env;
+        extended->locals = new(Table_t, .fallback=env->locals);
+        extended->namespace_bindings = new(Table_t, .fallback=env->namespace_bindings);
+        extended->libname = env->libname;
+        return compile_top_level_code(extended, extend->body);
     }
     case Extern: return CORD_EMPTY;
     case Block: {
@@ -4358,30 +4362,38 @@ CORD compile_statement_type_header(env_t *env, Path_t header_path, ast_t *ast)
 
 CORD compile_statement_namespace_header(env_t *env, Path_t header_path, ast_t *ast)
 {
-    const char *ns_name = NULL;
+    env_t *ns_env = NULL;
     ast_t *block = NULL;
     switch (ast->tag) {
     case LangDef: {
         auto def = Match(ast, LangDef);
-        ns_name = def->name;
+        ns_env = namespace_env(env, def->name);
         block = def->namespace;
         break;
     }
     case Extend: {
         auto extend = Match(ast, Extend);
-        ns_name = extend->name;
+        ns_env = namespace_env(env, extend->name);
+
+        env_t *extended = new(env_t);
+        *extended = *ns_env;
+        extended->locals = new(Table_t, .fallback=env->locals);
+        extended->namespace_bindings = new(Table_t, .fallback=env->namespace_bindings);
+        extended->libname = env->libname;
+        ns_env = extended;
+
         block = extend->body;
         break;
     }
     case StructDef: {
         auto def = Match(ast, StructDef);
-        ns_name = def->name;
+        ns_env = namespace_env(env, def->name);
         block = def->namespace;
         break;
     }
     case EnumDef: {
         auto def = Match(ast, EnumDef);
-        ns_name = def->name;
+        ns_env = namespace_env(env, def->name);
         block = def->namespace;
         break;
     }
@@ -4465,7 +4477,7 @@ CORD compile_statement_namespace_header(env_t *env, Path_t header_path, ast_t *a
     }
     default: return CORD_EMPTY;
     }
-    env_t *ns_env = namespace_env(env, ns_name);
+    assert(ns_env);
     CORD header = CORD_EMPTY;
     for (ast_list_t *stmt = block ? Match(block, Block)->statements : NULL; stmt; stmt = stmt->next) {
         header = CORD_all(header, compile_statement_namespace_header(ns_env, header_path, stmt->ast));
diff --git a/src/typecheck.c b/src/typecheck.c
index ff609435..648ffbc8 100644
--- a/src/typecheck.c
+++ b/src/typecheck.c
@@ -274,9 +274,23 @@ void prebind_statement(env_t *env, ast_t *statement)
     case Extend: {
         auto extend = Match(statement, Extend);
         env_t *ns_env = namespace_env(env, extend->name);
-        ns_env->libname = env->libname;
+        env_t *extended = new(env_t);
+        *extended = *ns_env;
+        extended->locals = new(Table_t, .fallback=env->locals);
+        extended->namespace_bindings = new(Table_t, .fallback=env->namespace_bindings);
+        extended->libname = env->libname;
         for (ast_list_t *stmt = extend->body ? Match(extend->body, Block)->statements : NULL; stmt; stmt = stmt->next)
-            prebind_statement(ns_env, stmt->ast);
+            prebind_statement(extended, stmt->ast);
+        Array_t new_bindings = extended->locals->entries;
+        for (int64_t i = 0; i < new_bindings.length; i++) {
+            struct { const char *name; binding_t *binding; } *entry = new_bindings.data + i*new_bindings.stride;
+            binding_t *clobbered = Table$str_get(*ns_env->locals, entry->name);
+            if (clobbered && !type_eq(clobbered->type, entry->binding->type))
+                code_err(statement, "This `extend` block overwrites the binding for ", quoted(entry->name),
+                         " in the original namespace (with type ", type_to_str(clobbered->type), ") with a new binding with type ",
+                         type_to_str(entry->binding->type));
+            Table$str_set(ns_env->locals, entry->name, entry->binding);
+        }
         break;
     }
     default: break;
@@ -448,9 +462,23 @@ void bind_statement(env_t *env, ast_t *statement)
     case Extend: {
         auto extend = Match(statement, Extend);
         env_t *ns_env = namespace_env(env, extend->name);
-        ns_env->libname = env->libname;
+        env_t *extended = new(env_t);
+        *extended = *ns_env;
+        extended->locals = new(Table_t, .fallback=env->locals);
+        extended->namespace_bindings = new(Table_t, .fallback=env->namespace_bindings);
+        extended->libname = env->libname;
         for (ast_list_t *stmt = extend->body ? Match(extend->body, Block)->statements : NULL; stmt; stmt = stmt->next)
-            bind_statement(ns_env, stmt->ast);
+            bind_statement(extended, stmt->ast);
+        Array_t new_bindings = extended->locals->entries;
+        for (int64_t i = 0; i < new_bindings.length; i++) {
+            struct { const char *name; binding_t *binding; } *entry = new_bindings.data + i*new_bindings.stride;
+            binding_t *clobbered = Table$str_get(*ns_env->locals, entry->name);
+            if (clobbered && !type_eq(clobbered->type, entry->binding->type))
+                code_err(statement, "This `extend` block overwrites the binding for ", quoted(entry->name),
+                         " in the original namespace (with type ", type_to_str(clobbered->type), ") with a new binding with type ",
+                         type_to_str(entry->binding->type));
+            Table$str_set(ns_env->locals, entry->name, entry->binding);
+        }
         break;
     }
     case Use: {