Wasm support

packaging/dependencies.nix

@@ -80,4 +80,6 @@ scope: {
         buildPhase = lib.replaceStrings [ "--without-python" ] [ "" ] old.buildPhase;
         installPhase = lib.replaceStrings [ "--without-python" ] [ "" ] old.installPhase;
       });
+
+  wasmtime = pkgs.callPackage ./wasmtime.nix { };
 }

packaging/wasmtime.nix

@@ -0,0 +1,74 @@
+# Stripped-down version of https://github.com/NixOS/nixpkgs/blob/master/pkgs/by-name/wa/wasmtime/package.nix,
+# license: https://github.com/NixOS/nixpkgs/blob/master/COPYING
+{
+  lib,
+  stdenv,
+  rust_1_89,
+  fetchFromGitHub,
+  cmake,
+  enableShared ? !stdenv.hostPlatform.isStatic,
+  enableStatic ? stdenv.hostPlatform.isStatic,
+}:
+rust_1_89.packages.stable.rustPlatform.buildRustPackage (finalAttrs: {
+  pname = "wasmtime";
+  version = "40.0.2";
+
+  src = fetchFromGitHub {
+    owner = "bytecodealliance";
+    repo = "wasmtime";
+    tag = "v${finalAttrs.version}";
+    hash = "sha256-4y9WpCdyuF/Tp2k/1d5rZxwYunWNdeibEsFgHcBC52Q=";
+    fetchSubmodules = true;
+  };
+
+  # Disable cargo-auditable until https://github.com/rust-secure-code/cargo-auditable/issues/124 is solved.
+  auditable = false;
+
+  cargoHash = "sha256-aTPgnuBvOIqg1+Sa2ZLdMTLujm8dKGK5xpZ3qHpr3f8=";
+  cargoBuildFlags = [
+    "--package"
+    "wasmtime-c-api"
+    "--no-default-features"
+    "--features cranelift,wasi,pooling-allocator,wat,demangle,gc-null"
+  ];
+
+  outputs = [
+    "out"
+    "lib"
+  ];
+
+  nativeBuildInputs = [
+    cmake
+  ];
+
+  doCheck =
+    with stdenv.buildPlatform;
+    # SIMD tests are only executed on platforms that support all
+    # required processor features (e.g. SSE3, SSSE3 and SSE4.1 on x86_64):
+    # https://github.com/bytecodealliance/wasmtime/blob/v9.0.0/cranelift/codegen/src/isa/x64/mod.rs#L220
+    (isx86_64 -> sse3Support && ssse3Support && sse4_1Support)
+    &&
+      # The dependency `wasi-preview1-component-adapter` fails to build because of:
+      # error: linker `rust-lld` not found
+      !isAarch64;
+
+  postInstall =
+    let
+      inherit (stdenv.hostPlatform.rust) cargoShortTarget;
+    in
+    ''
+      moveToOutput lib $lib
+      ${lib.optionalString (!enableShared) "rm -f $lib/lib/*.so{,.*}"}
+      ${lib.optionalString (!enableStatic) "rm -f $lib/lib/*.a"}
+
+      # copy the build.rs generated c-api headers
+      # https://github.com/rust-lang/cargo/issues/9661
+      mkdir -p $out
+      cp -r target/${cargoShortTarget}/release/build/wasmtime-c-api-impl-*/out/include $out/include
+    ''
+    + lib.optionalString stdenv.hostPlatform.isDarwin ''
+      install_name_tool -id \
+        $lib/lib/libwasmtime.dylib \
+        $lib/lib/libwasmtime.dylib
+    '';
+})

src/libexpr/include/nix/expr/eval.hh

@@ -1034,6 +1034,12 @@ public:
     [[nodiscard]] StringMap
     realiseContext(const NixStringContext & context, StorePathSet * maybePaths = nullptr, bool isIFD = true);
 
+    /**
+     * Coerce `v` to a path and realise it, i.e. build anything in the value's string context using `realiseContext()`.
+     */
+    SourcePath realisePath(
+        const PosIdx pos, Value & v, std::optional<SymlinkResolution> resolveSymlinks = SymlinkResolution::Full);
+
     /**
      * Realise the given string with context, and return the string with outputs instead of downstream output
      * placeholders.

src/libexpr/meson.build

@@ -239,7 +239,7 @@ this_library = library(
   soversion : nix_soversion,
   dependencies : deps_public + deps_private + deps_other,
   include_directories : include_dirs,
-  link_args : linker_export_flags,
+  link_args : linker_export_flags + [ '-lwasmtime' ],
   link_whole : [ parser_library ],
   prelink : true, # For C++ static initializers
   install : true,

src/libexpr/package.nix

@@ -14,6 +14,7 @@
   boehmgc,
   nlohmann_json,
   toml11,
+  wasmtime,
 
   # Configuration Options
 
@@ -64,6 +65,7 @@ mkMesonLibrary (finalAttrs: {
 
   buildInputs = [
     toml11
+    wasmtime
   ];
 
   propagatedBuildInputs = [

src/libexpr/primops.cc

@@ -165,24 +165,20 @@ StringMap EvalState::realiseContext(const NixStringContext & context, StorePathS
     return res;
 }
 
-static SourcePath realisePath(
-    EvalState & state,
-    const PosIdx pos,
-    Value & v,
-    std::optional<SymlinkResolution> resolveSymlinks = SymlinkResolution::Full)
+SourcePath EvalState::realisePath(const PosIdx pos, Value & v, std::optional<SymlinkResolution> resolveSymlinks)
 {
     NixStringContext context;
 
-    auto path = state.coerceToPath(noPos, v, context, "while realising the context of a path");
+    auto path = coerceToPath(noPos, v, context, "while realising the context of a path");
 
     try {
-        if (!context.empty() && path.accessor == state.rootFS) {
-            auto rewrites = state.realiseContext(context);
+        if (!context.empty() && path.accessor == rootFS) {
+            auto rewrites = realiseContext(context);
             path = {path.accessor, CanonPath(rewriteStrings(path.path.abs(), rewrites))};
         }
         return resolveSymlinks ? path.resolveSymlinks(*resolveSymlinks) : path;
     } catch (Error & e) {
-        e.addTrace(state.positions[pos], "while realising the context of path '%s'", path);
+        e.addTrace(positions[pos], "while realising the context of path '%s'", path);
         throw;
     }
 }
@@ -302,7 +298,7 @@ static void scopedImport(EvalState & state, const PosIdx pos, SourcePath & path,
    argument. */
 static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * vScope, Value & v)
 {
-    auto path = realisePath(state, pos, vPath, std::nullopt);
+    auto path = state.realisePath(pos, vPath, std::nullopt);
     auto path2 = path.path.abs();
 
     // FIXME
@@ -456,7 +452,7 @@ extern "C" typedef void (*ValueInitializer)(EvalState & state, Value & v);
 /* Load a ValueInitializer from a DSO and return whatever it initializes */
 void prim_importNative(EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
-    auto path = realisePath(state, pos, *args[0]);
+    auto path = state.realisePath(pos, *args[0]);
 
     std::string sym(
         state.forceStringNoCtx(*args[1], pos, "while evaluating the second argument passed to builtins.importNative"));
@@ -2003,7 +1999,7 @@ static void prim_pathExists(EvalState & state, const PosIdx pos, Value ** args,
             arg.type() == nString && (arg.string_view().ends_with("/") || arg.string_view().ends_with("/."));
 
         auto symlinkResolution = mustBeDir ? SymlinkResolution::Full : SymlinkResolution::Ancestors;
-        auto path = realisePath(state, pos, arg, symlinkResolution);
+        auto path = state.realisePath(pos, arg, symlinkResolution);
 
         auto st = path.maybeLstat();
         auto exists = st && (!mustBeDir || st->type == SourceAccessor::tDirectory);
@@ -2110,7 +2106,7 @@ static RegisterPrimOp primop_dirOf({
 /* Return the contents of a file as a string. */
 static void prim_readFile(EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
-    auto path = realisePath(state, pos, *args[0]);
+    auto path = state.realisePath(pos, *args[0]);
     auto s = path.readFile();
     if (s.find((char) 0) != std::string::npos)
         state.error<EvalError>("the contents of the file '%1%' cannot be represented as a Nix string", path)
@@ -2348,7 +2344,7 @@ static void prim_hashFile(EvalState & state, const PosIdx pos, Value ** args, Va
     if (!ha)
         state.error<EvalError>("unknown hash algorithm '%1%'", algo).atPos(pos).debugThrow();
 
-    auto path = realisePath(state, pos, *args[1]);
+    auto path = state.realisePath(pos, *args[1]);
 
     v.mkString(hashString(*ha, path.readFile()).to_string(HashFormat::Base16, false), state.mem);
 }
@@ -2400,7 +2396,7 @@ static const Value & fileTypeToString(EvalState & state, SourceAccessor::Type ty
 
 static void prim_readFileType(EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
-    auto path = realisePath(state, pos, *args[0], std::nullopt);
+    auto path = state.realisePath(pos, *args[0], std::nullopt);
     /* Retrieve the directory entry type and stringize it. */
     v = fileTypeToString(state, path.lstat().type);
 }
@@ -2418,7 +2414,7 @@ static RegisterPrimOp primop_readFileType({
 /* Read a directory (without . or ..) */
 static void prim_readDir(EvalState & state, const PosIdx pos, Value ** args, Value & v)
 {
-    auto path = realisePath(state, pos, *args[0]);
+    auto path = state.realisePath(pos, *args[0]);
 
     // Retrieve directory entries for all nodes in a directory.
     // This is similar to `getFileType` but is optimized to reduce system calls

src/libexpr/primops/meson.build

@@ -9,4 +9,5 @@ sources += files(
   'fetchMercurial.cc',
   'fetchTree.cc',
   'fromTOML.cc',
+  'wasm.cc',
 )