Avoid absolute path hack

.gitignore

@@ -1,3 +1,4 @@
 dist*
 result
 target
+cabal.project.local*

cabal.project

@@ -1,13 +1,5 @@
 packages: .
 
--- TODO a total hack
-package garnet
-  extra-lib-dirs:
-    /home/gthomas/code/garnet/rust/target/release
-    /home/gthomas/code/garnet/rust/target/debug
-  extra-include-dirs:
-    /home/gthomas/code/garnet/rust
-
 -- https://well-typed.com/blog/2026/02/hs-bindgen-alpha
 -- Haskell.nix doesn't seem to like `tag: release-0.1-alpha`, which the blog post suggests
 -- so we specify the equivalent commit SHAs manually instead

generate-bindings

@@ -5,7 +5,12 @@ set -euo pipefail
 
 # Generate Haskell FFI bindings from Rust source code.
 #
-# Pipeline: cargo build -> cbindgen -> patch header -> hs-bindgen
+# Pipeline:
+#   1. cargo build       - build the Rust static library
+#   2. cbindgen           - generate a C header from the Rust source
+#   3. awk                - patch the header for hs-bindgen compatibility
+#   4. hs-bindgen-cli     - generate Haskell FFI modules from the C header
+#   5. cabal configure    - point Cabal at the Rust build artifacts
 #
 # Prerequisites: run inside the Nix dev shell (provides gcc, cabal, cbindgen, hs-bindgen-cli).
 
@@ -30,18 +35,21 @@ cbindgen \
 echo "  Raw header written to $HEADER"
 
 # --- Step 3: Patch the header for hs-bindgen compatibility ---
+#
+# Two patches are needed, both due to hs-bindgen limitations with cbindgen's
+# output for #[repr(C, u8)] tagged enums:
+#
+# 1. cbindgen emits:    enum Shape_Tag { Circle, Rectangle, };
+#                       typedef uint8_t Shape_Tag;
+#    hs-bindgen needs:  typedef uint8_t Shape_Tag;
+#                       #define Circle 0
+#                       #define Rectangle 1
+#    See: no upstream issue yet for hs-bindgen
+#
+# 2. cbindgen emits:    union { ... };       (anonymous)
+#    hs-bindgen needs:  union { ... } body;  (named)
+#    See: https://github.com/well-typed/hs-bindgen/issues/1649
 echo "=== Patching header ==="
-
-# Two patches are needed:
-#
-# Patch 1: Replace cbindgen's enum pattern with typedef + #defines.
-#   cbindgen emits:  enum Shape_Tag { Circle, Rectangle, }; typedef uint8_t Shape_Tag;
-#   hs-bindgen needs: typedef uint8_t Shape_Tag; #define Circle 0 ...
-#
-# Patch 2: Name anonymous unions inside structs.
-#   cbindgen emits:  union { ... };
-#   hs-bindgen needs: union { ... } body;
-
 awk '
 # State machine for enum->typedef+define transformation
 /^enum [A-Za-z_][A-Za-z0-9_]* \{$/ {
@@ -94,11 +102,11 @@ pending_enum && /^typedef [A-Za-z0-9_]+ / {
 echo "  Patched header at $HEADER"
 
 # --- Step 4: Derive system include paths for hs-bindgen's libclang ---
-echo "=== Detecting system include paths ==="
-
+#
 # hs-bindgen uses libclang directly, which doesn't know about NixOS's
 # non-standard include locations. We extract them from cpp -v and pass
 # all of them — extra paths are harmless.
+echo "=== Detecting system include paths ==="
 CLANG_OPTIONS=()
 while IFS= read -r dir; do
   CLANG_OPTIONS+=("--clang-option" "-isystem$dir")
@@ -122,6 +130,17 @@ hs-bindgen-cli preprocess \
   "${CLANG_OPTIONS[@]}" \
   -I "$RUST_DIR" "$HEADER_NAME"
 
+# --- Step 6: Configure Cabal ---
+#
+# Point Cabal at the Rust static library and C header. This writes
+# cabal.project.local (gitignored) with absolute paths derived from
+# the current working directory, avoiding hardcoded paths in cabal.project.
+echo "=== Configuring Cabal ==="
+cabal configure \
+  --extra-lib-dirs="$RUST_DIR/target/debug" \
+  --extra-lib-dirs="$RUST_DIR/target/release" \
+  --extra-include-dirs="$RUST_DIR"
+
 echo "=== Done ==="
 echo "Generated Haskell bindings in $HASKELL_DIR/generated/"
 echo "Run 'cabal run' to test."