From 9aa6b9694bda85dcfadcbe3ac2b08871572b1aa2 Mon Sep 17 00:00:00 2001
From: Jooris Hadeler <jooris@hadeler.me>
Date: Wed, 11 Mar 2026 15:36:43 +0100
Subject: [PATCH] Feat: add -c flag to skip entry-point check

`fluxc -c <file>` compiles a source file without requiring a `main`
function, matching the convention of C compilers. Pass 4 (entry-point
validation) is skipped when `no_main` is set.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 fluxc/src/checker/mod.rs   | 44 ++++++++++++++++++++------------------
 fluxc/src/checker/tests.rs |  2 +-
 fluxc/src/cli.rs           | 10 ++++++++-
 fluxc/src/main.rs          |  2 +-
 4 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/fluxc/src/checker/mod.rs b/fluxc/src/checker/mod.rs
index 68f2af5..6f81793 100644
--- a/fluxc/src/checker/mod.rs
+++ b/fluxc/src/checker/mod.rs
@@ -166,7 +166,7 @@ fn value_struct_name(ty: &Ty) -> Option<&str> {
 
 // ── Entry point ────────────────────────────────────────────────────────────────
 
-pub fn check(program: &ast::Program<Parsed>) -> Vec<Diagnostic> {
+pub fn check(program: &ast::Program<Parsed>, no_main: bool) -> Vec<Diagnostic> {
     let mut checker = Checker::new();
 
     // ── Pass 1: collect struct names + function signatures ────────────────────
@@ -259,29 +259,31 @@ pub fn check(program: &ast::Program<Parsed>) -> Vec<Diagnostic> {
     }
 
     // ── Pass 4: verify entry point ────────────────────────────────────────────
-    let main_info = checker
-        .phi
-        .get("main")
-        .map(|e| (e.name_span, e.params.len(), e.ret.clone()));
-    match main_info {
-        None => {
-            checker.emit(
-                Diagnostic::error("program has no `main` function")
-                    .with_label(Label::primary(program.span)),
-            );
-        }
-        Some((name_span, param_count, ret)) => {
-            if param_count != 0 {
+    if !no_main {
+        let main_info = checker
+            .phi
+            .get("main")
+            .map(|e| (e.name_span, e.params.len(), e.ret.clone()));
+        match main_info {
+            None => {
                 checker.emit(
-                    Diagnostic::error("`main` must take no parameters")
-                        .with_label(Label::primary(name_span)),
+                    Diagnostic::error("program has no `main` function")
+                        .with_label(Label::primary(program.span)),
                 );
             }
-            if ret != Ty::Unit && ret != Ty::I32 && !ret.is_error() {
-                checker.emit(
-                    Diagnostic::error("`main` must return `()` or `i32`")
-                        .with_label(Label::primary(name_span)),
-                );
+            Some((name_span, param_count, ret)) => {
+                if param_count != 0 {
+                    checker.emit(
+                        Diagnostic::error("`main` must take no parameters")
+                            .with_label(Label::primary(name_span)),
+                    );
+                }
+                if ret != Ty::Unit && ret != Ty::I32 && !ret.is_error() {
+                    checker.emit(
+                        Diagnostic::error("`main` must return `()` or `i32`")
+                            .with_label(Label::primary(name_span)),
+                    );
+                }
             }
         }
     }
diff --git a/fluxc/src/checker/tests.rs b/fluxc/src/checker/tests.rs
index 1c9f0c7..8e010e7 100644
--- a/fluxc/src/checker/tests.rs
+++ b/fluxc/src/checker/tests.rs
@@ -19,7 +19,7 @@ mod tests {
             "parse errors: {:?}",
             parser.errors
         );
-        checker::check(&program)
+        checker::check(&program, false)
             .into_iter()
             .map(|d| d.message)
             .collect()
diff --git a/fluxc/src/cli.rs b/fluxc/src/cli.rs
index a98d00b..3de2755 100644
--- a/fluxc/src/cli.rs
+++ b/fluxc/src/cli.rs
@@ -23,6 +23,10 @@ pub fn print_help() {
         "-V".bold(),
         "--version".bold(),
     );
+    println!(
+        "  {}              Compile without requiring a `main` entry point",
+        "-c".bold(),
+    );
     println!();
     println!("{}", "ARGS:".bold().yellow());
     println!(
@@ -57,10 +61,13 @@ pub fn io_error(path: &str, err: std::io::Error) -> ! {
 
 pub struct Opts {
     pub files: Vec<String>,
+    /// `-c`: compile without requiring a `main` entry point.
+    pub no_main: bool,
 }
 
 pub fn parse_args() -> Opts {
     let mut files = Vec::new();
+    let mut no_main = false;
 
     for arg in std::env::args().skip(1) {
         match arg.as_str() {
@@ -72,6 +79,7 @@ pub fn parse_args() -> Opts {
                 print_version();
                 process::exit(0);
             }
+            "-c" => no_main = true,
             flag if flag.starts_with('-') => {
                 fatal(&format!("unknown option `{flag}`"));
             }
@@ -83,5 +91,5 @@ pub fn parse_args() -> Opts {
         fatal("no input files — at least one source file is required");
     }
 
-    Opts { files }
+    Opts { files, no_main }
 }
diff --git a/fluxc/src/main.rs b/fluxc/src/main.rs
index 7b46711..075f00a 100644
--- a/fluxc/src/main.rs
+++ b/fluxc/src/main.rs
@@ -26,7 +26,7 @@ fn main() {
         }
 
         if parser.errors.is_empty() {
-            let sema_errors = checker::check(&program);
+            let sema_errors = checker::check(&program, opts.no_main);
             for diag in &sema_errors {
                 eprint!("{}", diag.render(&content, path));
                 had_errors = true;