From bd5bbdebf116bb03da335d0e18a55a5597b55548 Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Tue, 29 Jul 2025 06:04:29 +0900
Subject: feat: function main() now returns zero if no return value are
 explicitly provided

---
 codegen.c    |  4 ++++
 main.c       |  1 -
 tests/064.sh | 22 ++++++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 tests/064.sh

diff --git a/codegen.c b/codegen.c
index 2240b22..d290e95 100644
--- a/codegen.c
+++ b/codegen.c
@@ -437,6 +437,10 @@ void codegen_func(CodeGen* g, AstNode* ast) {
 
     codegen_func_prologue(g, ast);
     codegen_stmt(g, ast->node_body);
+    if (string_equals_cstr(&ast->name, "main")) {
+        // C99: 5.1.2.2.3
+        printf("  mov rax, 0\n");
+    }
     codegen_func_epilogue(g, ast);
 
     printf("\n");
diff --git a/main.c b/main.c
index e9a4fa0..34a847f 100644
--- a/main.c
+++ b/main.c
@@ -26,5 +26,4 @@ int main(int argc, char** argv) {
     Program* prog = parse(tokens);
     analyze(prog);
     codegen(prog);
-    return 0;
 }
diff --git a/tests/064.sh b/tests/064.sh
new file mode 100644
index 0000000..80fba4f
--- /dev/null
+++ b/tests/064.sh
@@ -0,0 +1,22 @@
+set -e
+
+# C99: 5.1.2.2.3
+bash ../../test_exit_code.sh 0 <<'EOF'
+int main() {
+}
+EOF
+
+bash ../../test_exit_code.sh 0 <<'EOF'
+int main() {
+    1 + 2 + 3;
+}
+EOF
+
+bash ../../test_exit_code.sh 0 <<'EOF'
+int main() {
+    if (1) {
+    } else {
+        return 1;
+    }
+}
+EOF
-- 
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