wasm32-wasi support (#1179)

.buildkite/primer-wasm.yaml

@@ -0,0 +1,9 @@
+agents:
+  public: "true"
+  os: "linux"
+
+steps:
+  - label: ":haskell: :linux: Primer Wasm targets"
+    command: |
+      nix develop .#wasm --print-build-logs --command make wasm32-update
+      nix develop .#wasm --print-build-logs --command make wasm32-test-opt

Makefile

@@ -12,6 +12,15 @@ $(targets):
 	$(MAKE) -C primer-service $@
 	$(MAKE) -C primer-benchmark $@
 
+wasm32-update:
+	wasm32-wasi-cabal update
+
+wasm32 = wasm32-build wasm32-build-opt wasm32-configure wasm32-check wasm32-test wasm32-test-opt wasm32-clean
+
+$(wasm32):
+	$(MAKE) -C primer $@
+	$(MAKE) -C primer-api $@
+
 weeder:
 	cabal build all --enable-benchmarks --enable-tests
 	weeder
@@ -21,4 +30,4 @@ openapi.json: build
 	cabal run -v0 primer-service:exe:primer-openapi > $@
 	openapi-generator-cli validate --recommend -i $@
 
-.PHONY: $(targets) weeder
+.PHONY: $(targets) $(wasm32-targets) weeder

cabal.project

@@ -9,7 +9,7 @@ packages:
 
 optimization: 0
 
-allow-newer: hedgehog-classes:hedgehog
+allow-newer: hedgehog-classes:hedgehog,hedgehog-classes:pretty-show,hedgehog:pretty-show
 
 package *
   ghc-options: -fwrite-ide-info
@@ -24,6 +24,10 @@ package primer-api
 package primer-service
   test-options: "--size-cutoff=32768"
 
+if arch(wasm32)
+  package tasty
+    flags: -unix
+
 -- We need a newer version of Selda than what's been released to
 -- Hackage, plus some GHC 9.6 fixes from a community fork.
 source-repository-package
@@ -39,3 +43,34 @@ source-repository-package
   tag: 54c12169ce8cd46a7b3c698f65cea55e41a13fe6
   subdir: selda-sqlite
   --sha256: 0q8m8asmb83mpa3j3adlrhc446xif7gv6lql20gv05k33lmbjfhg
+
+-- Wasm workarounds.
+
+-- Upstream requires `happy` at build time, which doesn't work on Wasm
+-- targets.
+source-repository-package
+  type: git
+  location: https://github.com/hackworthltd/pretty-show
+  tag: 91d119cb0e3c5f7d866589b25158739580c8fc88
+  --sha256: sha256-mu8Eq0Sg6nCF8C2sXB6ebZcLhz8TVZAbNMiorA7RVc8=
+
+-- Upstream depends on Posix types unavailable in Wasm.
+source-repository-package
+  type: git
+  location: https://github.com/hackworthltd/semirings
+  tag: 369f696d9d00fe004b16b0de08888fee7a3d08c3
+  --sha256: sha256-kkHCp4Y9IqMXGaDyW5UpsmRjy0ZWZkVSo1nOhpgZUQ0=
+
+-- Upstream uses custom setup, which breaks on Wasm.
+source-repository-package
+  type: git
+  location: https://github.com/cdepillabout/pretty-simple
+  tag: 6fb9b281800ad045925c7344ceb9fd293d86c3b9
+  --sha256: sha256-1gsYj/iznEUCeQ1f5Xk7w54h9FLJSNrIR9V3p4eaRYk=
+
+-- Upstream doesn't want to support Wasm while it's "experimental."
+source-repository-package
+  type: git
+  location: https://github.com/amesgen/splitmix
+  tag: 83b906c4bcdc2720546f1779a16eb65e8e12ecba
+  --sha256: sha256-sR+Ne56SBzVbPfC7AJeQZn20YDfFwBDpRI873cTm1nU=

docs/development-guide-toc.md

@@ -27,3 +27,4 @@ the various packages' Haddocks.
 * [Primitives](primitives.md)
 * [Database ops](database.md)
 * [Benchmarking](benchmarking.md)
+* [WebAssembly support](wasm.md)

docs/wasm.md

@@ -0,0 +1,43 @@
+# WebAssembly (Wasm) support
+
+**Note**: WebAssembly support is currently very preliminary.
+
+For horizontal scalability reasons, we would like to run the `primer`
+and `primer-api` packages in the student's browser, rather than on a
+backend server. Therefore, we'd like to compile these packages to a
+`wasm32-wasi` target and call the (native) Primer API from TypeScript.
+
+Currently, we can compile these two packages to `wasm32-wasi`, but
+with the following caveats:
+
+1. Neither `haskell.nix` nor `nixpkgs.haskellPackages` support the
+   `wasm32-wasi` cross-target at the moment, so we can only build Wasm
+   targets directly via `wasm32-wasi-cabal` and `wasm32-wasi-ghc`. For
+   interactive development, we provide a special `nix develop` shell
+   which provides the necessary tools:
+
+   ```sh
+   nix develop .#wasm
+   ```
+
+   Note that the required tools are currently only available for
+   `x86_64-linux` Nix systems, so the special `wasm` Nix shell only
+   exists for that platform.
+
+2. Once you're in the special Wasm shell, it's advisable to use the
+   special `wasm32` `Makefile` targets. To build the libraries, run:
+
+   ```sh
+   make wasm32-configure
+   make wasm32-build
+   ```
+
+   To build the tests and run them using the `wasmtime` runtime, run:
+
+   ```sh
+   make wasm32-test
+   ```
+
+   The `wasm32-test`, in particular, needs to run several steps that
+   you'd otherwise need to run by hand in order to work around
+   `wasmtime` issues.

flake.nix

@@ -19,6 +19,8 @@
     nixpkgs.follows = "haskell-nix/nixpkgs-unstable";
     hacknix.inputs.nixpkgs.follows = "nixpkgs";
     pre-commit-hooks-nix.inputs.nixpkgs.follows = "nixpkgs";
+
+    ghc-wasm.url = "git+https://gitlab.haskell.org/ghc/ghc-wasm-meta";
   };
 
   outputs = inputs@ { flake-parts, ... }:
@@ -305,7 +307,25 @@
             })
             // primerFlake.apps;
 
-          devShells.default = primerFlake.devShell;
+          devShells = {
+            default = primerFlake.devShell;
+          } // (pkgs.lib.optionalAttrs (system == "x86_64-linux")) {
+            # Unfortunately, this is only available on x86_64-linux.
+            wasm = pkgs.mkShell {
+              packages = with inputs.ghc-wasm.packages.${system};
+                [
+                  wasm32-wasi-ghc-9_6
+                  wasm32-wasi-cabal-9_6
+                  wasmtime
+
+                  pkgs.gnumake
+
+                  # We need to run native `tasty-discover` at compile
+                  # time, because we can't do it via `wasmtime`.
+                  (pkgs.haskell-nix.tool ghcVersion "tasty-discover" { })
+                ];
+            };
+          };
 
           # This is a non-standard flake output, but we don't want to
           # include benchmark runs in `packages`, because we don't

primer-api/.gitignore

@@ -0,0 +1 @@
+test/TestsWasm32.hs

primer-api/Makefile

@@ -3,23 +3,47 @@
 # Most commands assume you're running this from the top-level `nix
 # develop` shell.
 
+wasm32-primer-api-test	:= $(shell wasm32-wasi-cabal list-bin -v0 test:primer-api-test)
+wasm32-primer-api-test-opt	:= $(shell wasm32-wasi-cabal list-bin -O2 -v0 test:primer-api-test)
+
 build:
 	cabal build
 
+wasm32-build:
+	wasm32-wasi-cabal build
+
+wasm32-build-opt:
+	wasm32-wasi-cabal build -O2
+
 configure:
 	cabal configure
 
+wasm32-configure:
+	wasm32-wasi-cabal configure
+
 check:	test
 
-test:
-	cabal test
+wasm32-check:	wasm32-test
+
+wasm32-test:
+	tasty-discover test/Test.hs _ test/TestsWasm32.hs --tree-display
+	wasm32-wasi-cabal build test:primer-api-test
+	wasmtime --dir test::test "$(wasm32-primer-api-test)"
+
+wasm32-test-opt: wasm32-build-opt
+	tasty-discover test/Test.hs _ test/TestsWasm32.hs --tree-display
+	wasm32-wasi-cabal build -O2 test:primer-api-test
+	wasmtime --dir test::test "$(wasm32-primer-api-test-opt)"
 
 docs:
 	cabal haddock
 
 clean:
 	cabal clean
 
+wasm32-clean:
+	wasm32-wasi-cabal clean
+
 bench:
 
 realclean: