all: add Nix flake file

This adds a flake.nix file that makes it possible to quickly create a
development environment.

You can download Nix here, for use on your Linux or macOS system:
https://nixos.org/download.html

After you have installed Nix, you can enter the development environment
as follows:

    nix develop

This drops you into a bash shell, where you can install TinyGo simply
using the following command:

    go install

That's all! Assuming you've set up your $PATH correctly, you can now use
the tinygo command as usual:

    tinygo version

You can also do many other things from this environment. Building and
flashing should work as you're used to: it's not a VM or container so
there are no access restrictions.

.github/workflows/nix.yml

@@ -0,0 +1,43 @@
+name: Nix
+
+on:
+  pull_request:
+  push:
+    branches:
+      - dev
+      - release
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  nix-test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Pull musl
+        run: |
+            git submodule update --init lib/musl
+      - name: Restore LLVM source cache
+        uses: actions/cache/restore@v3
+        id: cache-llvm-source
+        with:
+          key: llvm-source-16-linux-nix-v1
+          path: |
+            llvm-project/compiler-rt
+      - name: Download LLVM source
+        if: steps.cache-llvm-source.outputs.cache-hit != 'true'
+        run: make llvm-source
+      - name: Save LLVM source cache
+        uses: actions/cache/save@v3
+        if: steps.cache-llvm-source.outputs.cache-hit != 'true'
+        with:
+          key: ${{ steps.cache-llvm-source.outputs.cache-primary-key }}
+          path: |
+            llvm-project/compiler-rt
+      - uses: cachix/install-nix-action@v22
+      - name: Test
+        run: |
+          nix develop --ignore-environment --keep HOME --command bash -c "go install && ~/go/bin/tinygo version && ~/go/bin/tinygo build ./testdata/cgo"

compileopts/config.go

@@ -275,7 +275,8 @@ func (c *Config) CFlags(libclang bool) []string {
 	case "darwin-libSystem":
 		root := goenv.Get("TINYGOROOT")
 		cflags = append(cflags,
-			"--sysroot="+filepath.Join(root, "lib/macos-minimal-sdk/src"),
+			"-nostdlibinc",
+			"-isystem", filepath.Join(root, "lib/macos-minimal-sdk/src/usr/include"),
 		)
 	case "picolibc":
 		root := goenv.Get("TINYGOROOT")
@@ -304,7 +305,8 @@ func (c *Config) CFlags(libclang bool) []string {
 		root := goenv.Get("TINYGOROOT")
 		path, _ := c.LibcPath("mingw-w64")
 		cflags = append(cflags,
-			"--sysroot="+path,
+			"-nostdlibinc",
+			"-isystem", filepath.Join(path, "include"),
 			"-isystem", filepath.Join(root, "lib", "mingw-w64", "mingw-w64-headers", "crt"),
 			"-isystem", filepath.Join(root, "lib", "mingw-w64", "mingw-w64-headers", "defaults", "include"),
 			"-D_UCRT",

flake.nix

@@ -0,0 +1,63 @@
+# A Nix flake file, mainly intended for developing TinyGo.
+# You can download Nix here, for use on your Linux or macOS system:
+#   https://nixos.org/download.html
+# After you have installed Nix, you can enter the development environment as
+# follows:
+#
+#   nix develop
+#
+# This drops you into a bash shell, where you can install TinyGo simply using
+# the following command:
+#
+#   go install
+#
+# That's all! Assuming you've set up your $PATH correctly, you can now use the
+# tinygo command as usual:
+#
+#   tinygo version
+#
+# You can also do many other things from this environment. Building and flashing
+# should work as you're used to: it's not a VM or container so there are no
+# access restrictions and you're running in the same host environment - just
+# with a slightly different set of tools available.
+{
+  inputs = {
+    # Use a recent stable release, but fix the version to make it reproducible.
+    # This version should be updated from time to time.
+    nixpkgs.url = "nixpkgs/nixos-23.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      with pkgs;
+      {
+        devShells.default = mkShell {
+          buildInputs = [
+            # These dependencies are required for building tinygo (go install).
+            go
+            llvmPackages_16.llvm
+            llvmPackages_16.libclang
+            # Additional dependencies needed at runtime, for building and/or
+            # flashing.
+            llvmPackages_16.lld
+            avrdude
+            binaryen
+            # Additional dependencies needed for on-chip debugging.
+            # These tools are rather big (especially GDB) and not frequently
+            # used, so are commented out. On-chip debugging is still possible if
+            # these tools are available in the host environment.
+            #gdb
+            #openocd
+          ];
+          shellHook= ''
+            # Ugly hack to make the Clang resources directory available.
+            # Perhaps there is a cleaner way to do it, but this works.
+            export GOFLAGS="\"-ldflags=-X github.com/tinygo-org/tinygo/goenv.clangResourceDir=${llvmPackages_16.clang.cc.lib}/lib/clang/16"\"
+          '';
+        };
+      }
+    );
+}

goenv/goenv.go

@@ -43,6 +43,12 @@ var hasBuiltinTools = false
 // directory.
 var TINYGOROOT string
 
+// If a particular Clang resource dir must always be used and TinyGo can't
+// figure out the directory using heuristics, this global can be set using a
+// linker flag.
+// This is needed for Nix.
+var clangResourceDir string
+
 // Variables read from a `go env` command invocation.
 var goEnvVars struct {
 	GOPATH    string
@@ -298,6 +304,15 @@ func isSourceDir(root string) bool {
 // In that case, the resource dir is always returned (even when linking
 // dynamically against LLVM) because libclang always needs this directory.
 func ClangResourceDir(libclang bool) string {
+	if clangResourceDir != "" {
+		// The resource dir is forced to a particular value at build time.
+		// This is needed on Nix for example, where Clang and libclang don't
+		// know their own resource dir.
+		// Also see:
+		// https://discourse.nixos.org/t/why-is-the-clang-resource-dir-split-in-a-separate-package/34114
+		return clangResourceDir
+	}
+
 	if !hasBuiltinTools && !libclang {
 		// Using external tools, so the resource dir doesn't need to be
 		// specified. Clang knows where to find it.