add error for shadowing a type

closes #61

Author: andrewrk

src/analyze.cpp

@@ -2072,6 +2072,18 @@ static VariableTableEntry *add_local_var(CodeGen *g, AstNode *source_node, Block
         if (existing_var) {
             add_node_error(g, source_node, buf_sprintf("redeclaration of variable '%s'", buf_ptr(name)));
             variable_entry->type = g->builtin_types.entry_invalid;
+        } else {
+            auto primitive_table_entry = g->primitive_type_table.maybe_get(name);
+            TypeTableEntry *type;
+            if (primitive_table_entry) {
+                type = primitive_table_entry->value;
+            } else {
+                type = find_container(context, name);
+            }
+            if (type) {
+                add_node_error(g, source_node, buf_sprintf("variable shadows type '%s'", buf_ptr(&type->name)));
+                variable_entry->type = g->builtin_types.entry_invalid;
+            }
         }
 
         context->variable_table.put(&variable_entry->name, variable_entry);

test/run_tests.cpp

@@ -1501,6 +1501,16 @@ const foo = []u16{.x = 1024,};
     add_compile_fail_case("type variables must be constant", R"SOURCE(
 var foo = u8;
     )SOURCE", 1, ".tmp_source.zig:2:1: error: variable of type 'type' must be constant");
+
+    add_compile_fail_case("variables shadowing types", R"SOURCE(
+struct Foo {}
+struct Bar {}
+
+fn f(Foo: i32) => {
+    var Bar : i32;
+}
+    )SOURCE", 2, ".tmp_source.zig:5:6: error: variable shadows type 'Foo'",
+                 ".tmp_source.zig:6:5: error: variable shadows type 'Bar'");
 }
 
 static void print_compiler_invocation(TestCase *test_case) {