Bootstrap: the Finch compiler written in Finch

boot/ is a second Finch compiler written in Finch (lexer, parser, type checker and
an LLVM IR text generator, ~3k lines). Built by the C++ compiler it compiles itself;
stage 2 and stage 3 produce byte-identical IR. It covers the core language: functions,
structs, arrays, str, pointers, loops and modules (no C imports, sized numbers or defer),
copies values like the main compiler and leaves freeing memory to the operating system.

tests/boot.sh checks the fixpoint and runs the test programs it supports.
Also: shell(cmd) built-in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/boot.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# The self-hosted compiler (boot/) must
+#   1. build itself: stage1 (built by build/finch) -> stage2 -> stage3, with identical IR
+#   2. give the same output as build/finch on every test in tests/run it supports
+set -u
+cd "$(dirname "$0")/.."
+tmp=$(mktemp -d)
+trap 'rm -rf "$tmp"' EXIT
+
+build/finch build boot/main.fn -o "$tmp/boot1" || exit 1
+"$tmp/boot1" build boot/main.fn -o "$tmp/boot2" || exit 1
+"$tmp/boot1" ir boot/main.fn > "$tmp/stage2.ll"
+"$tmp/boot2" ir boot/main.fn > "$tmp/stage3.ll"
+if cmp -s "$tmp/stage2.ll" "$tmp/stage3.ll"; then
+    echo "bootstrap: stage 2 and stage 3 are identical ($(wc -l < "$tmp/stage3.ll") lines of IR)"
+else
+    echo "bootstrap: FAILED, stage 2 and stage 3 differ"
+    exit 1
+fi
+
+pass=0; failed=0; skipped=0
+for f in tests/run/*.fn; do
+    grep -q "^fn main" "$f" || continue
+    # the bootstrap compiler doesn't do C imports, sized numbers or defer
+    # (checked in the test and in the modules it imports)
+    files="$f"
+    for m in $(sed -n 's/^import \([a-z_]*\)$/\1/p' "$f"); do files="$files tests/run/$m.fn"; done
+    if grep -qE '^import "|^link |\b(u8|u16|u32|u64|i8|i16|i32|f32|f64)\b|defer |0x' $files; then
+        skipped=$((skipped + 1))
+        continue
+    fi
+    input="${f%.fn}.in"
+    [ -f "$input" ] || input=/dev/null
+    if ! "$tmp/boot2" build "$f" -o "$tmp/prog" > "$tmp/err" 2>&1; then
+        failed=$((failed + 1))
+        echo "FAIL (compile) $f"
+        head -3 "$tmp/err"
+        continue
+    fi
+    got=$("$tmp/prog" < "$input" 2>&1)
+    if [ "$got" == "$(cat "${f%.fn}.out")" ]; then
+        pass=$((pass + 1))
+    else
+        failed=$((failed + 1))
+        echo "FAIL (output) $f"
+        diff <(echo "$got") "${f%.fn}.out" | head -10
+    fi
+done
+echo "self-hosted compiler: $pass passed, $failed failed, $skipped skipped (features it doesn't have)"
+[ $failed -eq 0 ]