Feat: add -S flag to emit LLVM IR

`-S` stops the pipeline after IR emission and writes the `.ll` file
directly to the output path (default `<stem>.ll`). It implies `-c`
(no main required). Combined with `-o`, the IR goes to the specified
path.

Pipeline summary:
  (none)  →  emit → opt → llc → cc  →  executable
  -c      →  emit → opt → llc       →  <stem>.o
  -S      →  emit                   →  <stem>.ll

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fluxc/src/ast.rs

@@ -42,14 +42,25 @@ pub enum Ty {
     Char,
     Unit,
     // Pointer types
-    Ptr { mutable: bool, pointee: Box<Ty> },
-    OpaquePtr { mutable: bool },
+    Ptr {
+        mutable: bool,
+        pointee: Box<Ty>,
+    },
+    OpaquePtr {
+        mutable: bool,
+    },
     // Array type
-    Array { elem: Box<Ty>, size: u64 },
+    Array {
+        elem: Box<Ty>,
+        size: u64,
+    },
     // User-defined struct
     Struct(String),
     // Internal function signature (not user-facing)
-    FnSig { params: Vec<Ty>, ret: Box<Ty> },
+    FnSig {
+        params: Vec<Ty>,
+        ret: Box<Ty>,
+    },
     /// Unresolved integer type from a literal or an unannotated let-binding.
     /// Compatible with every concrete integer type; defaults to `i32` in
     /// error messages when no concrete type can be inferred.

fluxc/src/checker/mod.rs

@@ -10,6 +10,17 @@ use crate::diagnostics::{Diagnostic, Label};
 use crate::token::Span;
 use env::{FieldEntry, FuncTable, ParamEntry, StructTable};
 
+// ── Check result ───────────────────────────────────────────────────────────────
+
+/// The result of running the semantic checker. Carries both the diagnostics and
+/// the resolved symbol tables so that downstream passes (e.g. codegen) can
+/// reuse them without re-running the checker.
+pub struct CheckResult {
+    pub errors: Vec<Diagnostic>,
+    pub sigma: StructTable,
+    pub phi: FuncTable,
+}
+
 // ── Checker ────────────────────────────────────────────────────────────────────
 
 pub struct Checker {
@@ -166,7 +177,7 @@ fn value_struct_name(ty: &Ty) -> Option<&str> {
 
 // ── Entry point ────────────────────────────────────────────────────────────────
 
-pub fn check(program: &ast::Program<Parsed>, no_main: bool) -> Vec<Diagnostic> {
+pub fn check(program: &ast::Program<Parsed>, no_main: bool) -> CheckResult {
     let mut checker = Checker::new();
 
     // ── Pass 1: collect struct names + function signatures ────────────────────
@@ -288,5 +299,9 @@ pub fn check(program: &ast::Program<Parsed>, no_main: bool) -> Vec<Diagnostic> {
         }
     }
 
-    checker.errors
+    CheckResult {
+        errors: checker.errors,
+        sigma: checker.sigma,
+        phi: checker.phi,
+    }
 }

fluxc/src/checker/tests.rs

@@ -20,6 +20,7 @@ mod tests {
             parser.errors
         );
         checker::check(&program, false)
+            .errors
             .into_iter()
             .map(|d| d.message)
             .collect()

fluxc/src/cli.rs

@@ -24,9 +24,18 @@ pub fn print_help() {
         "--version".bold(),
     );
     println!(
-        "  {}              Compile without requiring a `main` entry point",
+        "  {}              Compile to object file (no `main` required, no linking)",
         "-c".bold(),
     );
+    println!(
+        "  {}              Emit LLVM IR and stop (implies `-c`)",
+        "-S".bold(),
+    );
+    println!(
+        "  {} {}      Write output to <file>",
+        "-o".bold(),
+        "<file>".bold(),
+    );
     println!();
     println!("{}", "ARGS:".bold().yellow());
     println!(
@@ -61,15 +70,22 @@ 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.
+    /// `-c`: compile to object file without requiring a `main` entry point.
     pub no_main: bool,
+    /// `-S`: emit LLVM IR text and stop (implies `-c`).
+    pub emit_ir: bool,
+    /// `-o <file>`: write final output to this path.
+    pub output: Option<String>,
 }
 
 pub fn parse_args() -> Opts {
     let mut files = Vec::new();
     let mut no_main = false;
+    let mut emit_ir = false;
+    let mut output: Option<String> = None;
+    let mut args = std::env::args().skip(1).peekable();
 
-    for arg in std::env::args().skip(1) {
+    while let Some(arg) = args.next() {
         match arg.as_str() {
             "-h" | "--help" => {
                 print_help();
@@ -80,6 +96,11 @@ pub fn parse_args() -> Opts {
                 process::exit(0);
             }
             "-c" => no_main = true,
+            "-S" => { emit_ir = true; no_main = true; }
+            "-o" => match args.next() {
+                Some(path) => output = Some(path),
+                None => fatal("option `-o` requires an argument"),
+            },
             flag if flag.starts_with('-') => {
                 fatal(&format!("unknown option `{flag}`"));
             }
@@ -91,5 +112,5 @@ pub fn parse_args() -> Opts {
         fatal("no input files — at least one source file is required");
     }
 
-    Opts { files, no_main }
+    Opts { files, no_main, emit_ir, output }
 }

fluxc/src/codegen/mod.rs

@@ -0,0 +1,120 @@
+pub mod emit;
+
+use std::path::Path;
+use std::process::{Command, Stdio};
+use std::{env, fs};
+
+use crate::ast::{self, Parsed};
+use crate::checker::CheckResult;
+use crate::cli::Opts;
+
+// ── Entry point ────────────────────────────────────────────────────────────────
+
+/// Compile a parsed + type-checked program.
+///
+/// Mode is controlled by `opts`:
+///
+/// | flags    | output              | pipeline              |
+/// |----------|---------------------|-----------------------|
+/// | (none)   | `<stem>` executable | emit → opt → llc → cc |
+/// | `-c`     | `<stem>.o`          | emit → opt → llc      |
+/// | `-S`     | `<stem>.ll`         | emit only             |
+///
+/// Tool overrides via environment variables:
+///   `FLUXC_OPT` (default `opt`), `FLUXC_LLC` (default `llc`),
+///   `FLUXC_CC`  (default `cc`).
+pub fn compile(
+    input_path: &str,
+    program: &ast::Program<Parsed>,
+    result: CheckResult,
+    opts: &Opts,
+) -> Result<(), String> {
+    // ── Derive output path ────────────────────────────────────────────────────
+    let stem = Path::new(input_path)
+        .file_stem()
+        .map(|s| s.to_string_lossy().into_owned())
+        .unwrap_or_else(|| "out".to_string());
+
+    let final_output = opts.output.clone().unwrap_or_else(|| {
+        if opts.emit_ir {
+            format!("{stem}.ll")
+        } else if opts.no_main {
+            format!("{stem}.o")
+        } else {
+            stem.clone()
+        }
+    });
+
+    // ── Step 1: emit LLVM IR ──────────────────────────────────────────────────
+    let ir = emit::emit_program(program, &result.sigma, &result.phi);
+
+    // `-S`: write IR directly to final output and stop.
+    if opts.emit_ir {
+        return fs::write(&final_output, &ir)
+            .map_err(|e| format!("cannot write {final_output}: {e}"));
+    }
+
+    // ── Temp paths (only used when compiling beyond IR) ───────────────────────
+    let tmp = env::temp_dir();
+    let raw_ll = tmp.join(format!("fluxc_{stem}.ll"));
+    let opt_ll = tmp.join(format!("fluxc_{stem}.opt.ll"));
+    let obj    = tmp.join(format!("fluxc_{stem}.o"));
+
+    fs::write(&raw_ll, &ir)
+        .map_err(|e| format!("cannot write IR to {}: {e}", raw_ll.display()))?;
+
+    // ── Step 2: opt ───────────────────────────────────────────────────────────
+    let opt_bin = tool_path("FLUXC_OPT", "opt");
+    run(
+        &opt_bin,
+        &["-O2", raw_ll.to_str().unwrap(), "-S", "-o", opt_ll.to_str().unwrap()],
+    )?;
+
+    // ── Step 3: llc ───────────────────────────────────────────────────────────
+    let llc_bin = tool_path("FLUXC_LLC", "llc");
+    run(
+        &llc_bin,
+        &[opt_ll.to_str().unwrap(), "-filetype=obj", "-o", obj.to_str().unwrap()],
+    )?;
+
+    // ── Step 4: link (skipped in `-c` mode) ───────────────────────────────────
+    if opts.no_main {
+        fs::copy(&obj, &final_output)
+            .map_err(|e| format!("cannot write {final_output}: {e}"))?;
+    } else {
+        let cc_bin = tool_path("FLUXC_CC", "cc");
+        run(&cc_bin, &[obj.to_str().unwrap(), "-o", &final_output])?;
+    }
+
+    // ── Clean up temp files ───────────────────────────────────────────────────
+    let _ = fs::remove_file(&raw_ll);
+    let _ = fs::remove_file(&opt_ll);
+    let _ = fs::remove_file(&obj);
+
+    Ok(())
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+fn tool_path(env_var: &str, default: &str) -> String {
+    env::var(env_var).unwrap_or_else(|_| default.to_string())
+}
+
+fn run(bin: &str, args: &[&str]) -> Result<(), String> {
+    let output = Command::new(bin)
+        .args(args)
+        .stdout(Stdio::inherit())
+        .stderr(Stdio::piped())
+        .output()
+        .map_err(|e| format!("failed to run `{bin}`: {e}"))?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        return Err(format!(
+            "`{bin}` exited with {}\n{}",
+            output.status,
+            stderr.trim_end()
+        ));
+    }
+    Ok(())
+}

fluxc/src/main.rs

@@ -5,6 +5,7 @@ use crate::parser::Parser;
 pub mod ast;
 pub mod checker;
 pub mod cli;
+pub mod codegen;
 pub mod diagnostics;
 pub mod lexer;
 pub mod parser;
@@ -14,6 +15,10 @@ fn main() {
     let opts = cli::parse_args();
     let mut had_errors = false;
 
+    // Collect (path, source, program, check_result) for all input files.
+    // We gate codegen on all files being error-free.
+    let mut compiled = Vec::new();
+
     for path in &opts.files {
         let content = fs::read_to_string(path).unwrap_or_else(|e| cli::io_error(path, e));
 
@@ -26,11 +31,24 @@ fn main() {
         }
 
         if parser.errors.is_empty() {
-            let sema_errors = checker::check(&program, opts.no_main);
-            for diag in &sema_errors {
+            let result = checker::check(&program, opts.no_main);
+            for diag in &result.errors {
                 eprint!("{}", diag.render(&content, path));
                 had_errors = true;
             }
+            compiled.push((path.clone(), program, result));
+        }
+    }
+
+    if had_errors {
+        process::exit(1);
+    }
+
+    // All files are clean — run codegen.
+    for (path, program, result) in compiled {
+        if let Err(e) = codegen::compile(&path, &program, result, &opts) {
+            eprintln!("{}: {e}", "error".to_string());
+            had_errors = true;
         }
     }