Phase 7.10: command-line args + buxc2 check/build working

Runtime:
- bux_argc()/bux_argv() — command-line arg access from Bux programs
- g_argc/g_argv globals — set by C main() wrapper

Compiler:
- C backend generates extern g_argc/g_argv + int main(argc,argv) wrapper
- main.bux reads args via bux_argc/bux_argv and passes to Cli_Run

buxc2 verified:
- buxc2 version — reads CLI args correctly
- buxc2 check <file.bux> — lexes, parses, type-checks, generates C
- buxc2 build <file.bux> <output.c> — writes C output

PLAN.md updated with Phase 7.10 status and remaining work.
All 18 examples pass, all unit tests pass.

PLAN.md

@@ -293,7 +293,32 @@ Phase 7.5 — Driver (depends on all):
 | `7.7` Port C backend | ✅ | `c_backend.bux` — C code generator | 266 |
 | `7.8` Port CLI | ✅ | `cli.bux` + `main.bux` — command dispatch | ~181 |
 | `7.9` Dogfooding | ✅ | `buxc` (Nim) compiles `buxc2` (Bux) — **WORKING BINARY** (88KB ELF x86-64) | — |
-| `7.10` Fix bootstrap loop | ⏳ | Once `buxc2 == buxc3`, we are self-hosted. Freeze Nim version as reference. | — |
+| `7.10` Bootstrap loop | 🔄 | `buxc2 check` works on `.bux` files. Full multi-file build needs sema/IR fixes. | 7.9 |
+
+### Phase 7.10 — Bootstrap Loop (In Progress)
+
+**Status:** `buxc2` can type-check (`check`) individual `.bux` files. Full self-compilation needs fixes in `buxc2`'s sema, HIR, and C backend.
+
+**What works:**
+- ✅ `buxc2 version` — shows version from command-line args
+- ✅ `buxc2 check <file.bux>` — lexes, parses, type-checks, generates C (validates pipeline)
+- ✅ `buxc2 build <file.bux> <output.c>` — writes generated C to file
+- ✅ Command-line args — `bux_argc()`/`bux_argv()` in runtime, `int main(argc, argv)` wrapper
+
+**What needs fixing in `buxc2`:**
+| Issue | Location | Description |
+|-------|----------|-------------|
+| `String` → `int` | `sema.bux` | `Sema_ResolveType("String")` returns `tyInt` instead of `tyStr` |
+| Function calls not in body | `hir_lower.bux` | `Lcx_LowerExpr` doesn't emit call expressions into function body |
+| No `int main()` wrapper | `c_backend.bux` | Missing `hasMain` detection and C main wrapper generation |
+| Single-file only | `cli.bux` | Cannot merge multiple `.bux` files with imports |
+
+**Bootstrap loop goal:**
+```
+buxc (Nim) → compile src_bux/*.bux → buxc2 (Bux binary)
+buxc2 (Bux) → compile src_bux/*.bux → buxc3 (Bux binary)
+compare buxc2 == buxc3 → SELF-HOSTED ✅
+```
 
 ### Phase 7.9 — Completed 2026-05-31 🎉
 

_selfhost/src/Main.bux

@@ -1,13 +1,22 @@
 // main.bux — Entry point for the Bux self-hosting compiler
 module Main {
 
+// C runtime for command-line args
+extern func bux_argc() -> int;
+extern func bux_argv(index: int) -> String;
+
 // Forward declaration from Cli module
 func Cli_Run(args: *String, argCount: int) -> int;
 
 func Main() -> int {
-    // In a full implementation, parse command-line arguments
-    // For now, just show version info
-    var emptyArgs: *String = null as *String;
-    return Cli_Run(emptyArgs, 0);
+    let count: int = bux_argc();
+    // Allocate array of String pointers
+    let args: *String = bux_alloc(count as uint * 8) as *String;
+    var i: int = 0;
+    while i < count {
+        args[i] = bux_argv(i);
+        i = i + 1;
+    }
+    return Cli_Run(args, count);
 }
 }

src/c_backend.nim

@@ -544,7 +544,11 @@ proc emitModule*(be: var CBackend, module: HirModule): string =
   # Generate C main wrapper if Bux Main exists
   if hasMain:
     be.emitLine("/* C entry point wrapper */")
+    be.emitLine("extern int g_argc;")
+    be.emitLine("extern char** g_argv;")
     be.emitLine("int main(int argc, char** argv) {")
+    be.emitLine("    g_argc = argc;")
+    be.emitLine("    g_argv = argv;")
     be.emitLine("    return Main();")
     be.emitLine("}")
     be.emitLine("")

src_bux/main.bux

@@ -1,13 +1,22 @@
 // main.bux — Entry point for the Bux self-hosting compiler
 module Main {
 
+// C runtime for command-line args
+extern func bux_argc() -> int;
+extern func bux_argv(index: int) -> String;
+
 // Forward declaration from Cli module
 func Cli_Run(args: *String, argCount: int) -> int;
 
 func Main() -> int {
-    // In a full implementation, parse command-line arguments
-    // For now, just show version info
-    var emptyArgs: *String = null as *String;
-    return Cli_Run(emptyArgs, 0);
+    let count: int = bux_argc();
+    // Allocate array of String pointers
+    let args: *String = bux_alloc(count as uint * 8) as *String;
+    var i: int = 0;
+    while i < count {
+        args[i] = bux_argv(i);
+        i = i + 1;
+    }
+    return Cli_Run(args, count);
 }
 }

stdlib/runtime.c

@@ -7,6 +7,16 @@
 #include <stdbool.h>
 #include <string.h>
 
+/* Command-line argument storage */
+int g_argc = 0;
+char** g_argv = NULL;
+
+int bux_argc(void) { return g_argc; }
+char* bux_argv(int index) {
+    if (index < 0 || index >= g_argc) return "";
+    return g_argv[index];
+}
+
 /* Memory allocation */
 void* bux_alloc(size_t size) {
     void* ptr = malloc(size);