rust: make pkgsCross.wasi32.rustPlatform.buildRustPackage work

lib/systems/examples.nix

@@ -353,6 +353,7 @@ rec {
 
   wasi32 = {
     config = "wasm32-unknown-wasi";
+    rustc.config = "wasm32-wasip1";
     useLLVM = true;
   };
 

pkgs/build-support/bintools-wrapper/default.nix

@@ -235,6 +235,12 @@ stdenvNoCC.mkDerivation {
         basename=$(basename "$variant")
         wrap $basename ${./ld-wrapper.sh} $variant
       done
+    '' + optionalString targetPlatform.isWasi ''
+      wrap ${targetPrefix}wasm-ld ${./ld-wrapper.sh} $ldPath/${targetPrefix}wasm-ld
+      # clang doesn't properly normalize the target triple[1] before using it as a search path,
+      # and rustc passes wasm32-wasi as `-target`, which gets used as is. Work around.
+      # [1] https://github.com/llvm/llvm-project/blob/ad7aeb0ff58ebd29f68adb85c64e8010639e2a76/clang/lib/Driver/Driver.cpp#L6187
+      ln -s $out/bin/${targetPrefix}wasm-ld $out/bin/wasm32-wasi-wasm-ld
     '';
 
   strictDeps = true;

pkgs/build-support/rust/lib/default.nix

@@ -14,18 +14,23 @@ rec {
   # passed on a build=x86_64/host=aarch64 compilation.
   envVars = let
 
-    ccForBuild = "${pkgsBuildHost.stdenv.cc}/bin/${pkgsBuildHost.stdenv.cc.targetPrefix}cc";
-    cxxForBuild = "${pkgsBuildHost.stdenv.cc}/bin/${pkgsBuildHost.stdenv.cc.targetPrefix}c++";
+    # should match pkgs/development/compilers/rust/rustc.nix
+    prefixForStdenv = stdenv: "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}";
+    ccForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang" else "gcc"}";
+    cxxForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang++" else "g++"}";
 
-    ccForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc";
-    cxxForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}c++";
+    ccForBuild = ccForStdenv pkgsBuildHost.stdenv;
+    cxxForBuild = cxxForStdenv pkgsBuildHost.stdenv;
+
+    ccForHost = ccForStdenv stdenv;
+    cxxForHost = cxxForStdenv stdenv;
 
     # Unfortunately we must use the dangerous `pkgsTargetTarget` here
     # because hooks are artificially phase-shifted one slot earlier
     # (they go in nativeBuildInputs, so the hostPlatform looks like
     # a targetPlatform to them).
-    ccForTarget = "${pkgsTargetTarget.stdenv.cc}/bin/${pkgsTargetTarget.stdenv.cc.targetPrefix}cc";
-    cxxForTarget = "${pkgsTargetTarget.stdenv.cc}/bin/${pkgsTargetTarget.stdenv.cc.targetPrefix}c++";
+    ccForTarget = ccForStdenv pkgsTargetTarget.stdenv;
+    cxxForTarget = cxxForStdenv pkgsTargetTarget.stdenv;
 
     rustBuildPlatform = stdenv.buildPlatform.rust.rustcTarget;
     rustBuildPlatformSpec = stdenv.buildPlatform.rust.rustcTargetSpec;

pkgs/development/compilers/rust/1_81.nix

@@ -32,18 +32,21 @@
 let
   llvmSharedFor =
     pkgSet:
-    pkgSet.llvmPackages_18.libllvm.override (
-      {
-        enableSharedLibraries = true;
-      }
-      // lib.optionalAttrs (stdenv.targetPlatform.useLLVM or false) {
-        # Force LLVM to compile using clang + LLVM libs when targeting pkgsLLVM
-        stdenv = pkgSet.stdenv.override {
-          allowedRequisites = null;
-          cc = pkgSet.llvmPackages_18.clangUseLLVM;
-        };
-      }
-    );
+    if !stdenv.targetPlatform.isWasi then
+      pkgSet.llvmPackages_18.libllvm.override (
+        {
+          enableSharedLibraries = true;
+        }
+        // lib.optionalAttrs (stdenv.targetPlatform.useLLVM or false) {
+          # Force LLVM to compile using clang + LLVM libs when targeting pkgsLLVM
+          stdenv = pkgSet.stdenv.override {
+            allowedRequisites = null;
+            cc = pkgSet.llvmPackages_18.clangUseLLVM;
+          };
+        }
+      )
+    else
+      pkgSet.llvmPackages_18.libllvm;
 in
 import ./default.nix
   {
@@ -59,7 +62,7 @@ import ./default.nix
 
     # Expose llvmPackages used for rustc from rustc via passthru for LTO in Firefox
     llvmPackages =
-      if (stdenv.targetPlatform.useLLVM or false) then
+      if ((stdenv.targetPlatform.useLLVM or false) && !stdenv.targetPlatform.isWasi) then
         callPackage (
           {
             pkgs,

pkgs/development/compilers/rust/rustc.nix

@@ -84,8 +84,8 @@ in stdenv.mkDerivation (finalAttrs: {
   # Reference: https://github.com/rust-lang/rust/blob/master/src/bootstrap/configure.py
   configureFlags = let
     prefixForStdenv = stdenv: "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}";
-    ccPrefixForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang" else "cc"}";
-    cxxPrefixForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang++" else "c++"}";
+    ccPrefixForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang" else "gcc"}";
+    cxxPrefixForStdenv = stdenv: "${prefixForStdenv stdenv}${if (stdenv.cc.isClang or false) then "clang++" else "g++"}";
     setBuild  = "--set=target.${stdenv.buildPlatform.rust.rustcTarget}";
     setHost   = "--set=target.${stdenv.hostPlatform.rust.rustcTarget}";
     setTarget = "--set=target.${stdenv.targetPlatform.rust.rustcTarget}";
@@ -167,6 +167,8 @@ in stdenv.mkDerivation (finalAttrs: {
     "${setHost}.musl-root=${pkgsBuildHost.targetPackages.stdenv.cc.libc}"
   ] ++ optionals stdenv.targetPlatform.isMusl [
     "${setTarget}.musl-root=${pkgsBuildTarget.targetPackages.stdenv.cc.libc}"
+  ] ++ optionals stdenv.targetPlatform.isWasi [
+    "${setTarget}.wasi-root=${pkgsBuildTarget.targetPackages.stdenv.cc.libc}"
   ] ++ optionals stdenv.targetPlatform.rust.isNoStdTarget [
     "--disable-docs"
   ] ++ optionals (stdenv.hostPlatform.isDarwin && stdenv.hostPlatform.isx86_64) [
@@ -223,6 +225,10 @@ in stdenv.mkDerivation (finalAttrs: {
     substituteInPlace compiler/rustc_target/src/spec/*/*.rs \
       --replace-quiet '"rust-lld"' '"lld"'
 
+    # Figuring out when this should be False is a rustc FIXME. Nixpkgs needs it false.
+    substituteInPlace compiler/rustc_target/src/spec/targets/wasm32_wasi*.rs \
+      --replace LinkSelfContainedDefault::True LinkSelfContainedDefault::False
+
     ${optionalString (!withBundledLLVM) "rm -rf src/llvm"}
 
     # Useful debugging parameter
@@ -262,7 +268,7 @@ in stdenv.mkDerivation (finalAttrs: {
   buildInputs = [ openssl ]
     ++ optionals stdenv.hostPlatform.isDarwin [ libiconv Security zlib ]
     ++ optional (!withBundledLLVM) llvmShared.lib
-    ++ optional (useLLVM && !withBundledLLVM) [
+    ++ optional (useLLVM && !withBundledLLVM && !stdenv.targetPlatform.isWasi) [
       llvmPackages.libunwind
       # Hack which is used upstream https://github.com/gentoo/gentoo/blob/master/dev-lang/rust/rust-1.78.0.ebuild#L284
       (runCommandLocal "libunwind-libgcc" {} ''

pkgs/development/libraries/wasilibc/default.nix

@@ -51,6 +51,11 @@ stdenv.mkDerivation {
 
   preFixup = ''
     ln -s $share/share/undefined-symbols.txt $out/lib/wasi.imports
+    # rustc build expects lib at the path where a make install would put them without the SYSROOT_* overrides
+    TARGET_TRIPLE=wasm32-wasip1
+    ln -s $out/lib/ $out/lib/$TARGET_TRIPLE
+    ln -s $dev/include $dev/include/$TARGET_TRIPLE
+    ln -s $share/share $share/share/$TARGET_TRIPLE
   '';
 
   passthru.tests = {