From daa3b6bfa32e3be1c434b20ba91f6a519304c81c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <superjoe30@gmail.com>
Date: Sat, 5 Dec 2015 21:04:57 -0700
Subject: [PATCH] add unused label error

---
 README.md             |  2 --
 src/analyze.cpp       | 18 ++++++++++++++++++
 src/semantic_info.hpp |  1 +
 test/run_tests.cpp    |  5 +++++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 4bb149bbc5..c63a8232a0 100644
--- a/README.md
+++ b/README.md
@@ -42,8 +42,6 @@ make
 
 ## Roadmap
 
- * parseh: unreachable <--> noreturn attribute
- * unused label error
  * loops
  * structs
  * tagged enums
diff --git a/src/analyze.cpp b/src/analyze.cpp
index 82d37de109..e53cda3b13 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -471,6 +471,7 @@ static TypeTableEntry * analyze_expression(CodeGen *g, ImportTableEntry *import,
                     assert(!node->codegen_node);
                     node->codegen_node = allocate<CodeGenNode>(1);
                     node->codegen_node->data.label_entry = table_entry->value;
+                    table_entry->value->used = true;
                 } else {
                     add_node_error(g, node,
                             buf_sprintf("use of undeclared label '%s'", buf_ptr(&node->data.go_to.name)));
@@ -758,6 +759,23 @@ static void analyze_top_level_declaration(CodeGen *g, ImportTableEntry *import,
                 node->codegen_node = allocate<CodeGenNode>(1);
                 node->codegen_node->data.fn_def_node.implicit_return_type = block_return_type;
                 node->codegen_node->data.fn_def_node.block_context = context;
+
+                {
+                    FnTableEntry *fn_table_entry = fn_proto_node->codegen_node->data.fn_proto_node.fn_table_entry;
+                    auto it = fn_table_entry->label_table.entry_iterator();
+                    for (;;) {
+                        auto *entry = it.next();
+                        if (!entry)
+                            break;
+
+                        LabelTableEntry *label_entry = entry->value;
+                        if (!label_entry->used) {
+                            add_node_error(g, label_entry->label_node,
+                                buf_sprintf("label '%s' defined but not used",
+                                    buf_ptr(&label_entry->label_node->data.label.name)));
+                        }
+                    }
+                }
             }
             break;
 
diff --git a/src/semantic_info.hpp b/src/semantic_info.hpp
index 6f4b7da8b3..3e3e87084a 100644
--- a/src/semantic_info.hpp
+++ b/src/semantic_info.hpp
@@ -41,6 +41,7 @@ struct ImportTableEntry {
 struct LabelTableEntry {
     AstNode *label_node;
     LLVMBasicBlockRef basic_block;
+    bool used;
 };
 
 struct FnTableEntry {
diff --git a/test/run_tests.cpp b/test/run_tests.cpp
index b37a4d17f4..8c33cc1b8f 100644
--- a/test/run_tests.cpp
+++ b/test/run_tests.cpp
@@ -466,6 +466,11 @@ fn f(a : unreachable) {}
 export fn f(a : void) {}
     )SOURCE", 1, ".tmp_source.zig:2:17: error: parameter of type 'void' not allowed on exported functions");
 
+    add_compile_fail_case("unused label", R"SOURCE(
+export fn f() {
+a_label:
+}
+    )SOURCE", 1, ".tmp_source.zig:3:1: error: label 'a_label' defined but not used");
 }
 
 static void print_compiler_invocation(TestCase *test_case, Buf *zig_stderr) {