Merge pull request #11024 from topolarity/wasi-stage2

stage2: Add limited WASI support for selfExePath and globalCacheDir

3 files changed, 33 insertions, 8 deletions

diff --git a/src/Cache.zig b/src/Cache.zig
index 993114905e..37cd7a7529 100644
--- a/src/Cache.zig
+++ b/src/Cache.zig
@@ -762,18 +762,22 @@ pub const Manifest = struct {
 
     fn downgradeToSharedLock(self: *Manifest) !void {
         if (!self.have_exclusive_lock) return;
-        const manifest_file = self.manifest_file.?;
-        try manifest_file.downgradeLock();
+        if (std.process.can_spawn or !builtin.single_threaded) { // Some targets (WASI) do not support flock
+            const manifest_file = self.manifest_file.?;
+            try manifest_file.downgradeLock();
+        }
         self.have_exclusive_lock = false;
     }
 
     fn upgradeToExclusiveLock(self: *Manifest) !void {
         if (self.have_exclusive_lock) return;
-        const manifest_file = self.manifest_file.?;
-        // Here we intentionally have a period where the lock is released, in case there are
-        // other processes holding a shared lock.
-        manifest_file.unlock();
-        try manifest_file.lock(.Exclusive);
+        if (std.process.can_spawn or !builtin.single_threaded) { // Some targets (WASI) do not support flock
+            const manifest_file = self.manifest_file.?;
+            // Here we intentionally have a period where the lock is released, in case there are
+            // other processes holding a shared lock.
+            manifest_file.unlock();
+            try manifest_file.lock(.Exclusive);
+        }
         self.have_exclusive_lock = true;
     }
 
diff --git a/src/introspect.zig b/src/introspect.zig
index 562d6b04f4..c0de4dc7f5 100644
--- a/src/introspect.zig
+++ b/src/introspect.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const builtin = @import("builtin");
 const mem = std.mem;
+const os = std.os;
 const fs = std.fs;
 const Compilation = @import("Compilation.zig");
 
@@ -80,5 +81,15 @@ pub fn resolveGlobalCacheDir(allocator: mem.Allocator) ![]u8 {
         }
     }
 
-    return fs.getAppDataDir(allocator, appname);
+    if (builtin.os.tag == .wasi) {
+        // On WASI, we have no way to get an App data dir, so we try to use a fixed
+        // Preopen path "/cache" as a last resort
+        const path = "/cache";
+
+        const file = os.fstatat(os.wasi.AT.FDCWD, path, 0) catch return error.CacheDirUnavailable;
+        if (file.filetype != .DIRECTORY) return error.CacheDirUnavailable;
+        return allocator.dupe(u8, path);
+    } else {
+        return fs.getAppDataDir(allocator, appname);
+    }
 }
diff --git a/src/main.zig b/src/main.zig
index e341a10f99..823eb91f33 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -162,6 +162,16 @@ pub fn main() anyerror!void {
         return mainArgs(gpa_tracy.allocator(), arena, args);
     }
 
+    // WASI: `--dir` instructs the WASM runtime to "preopen" a directory, making
+    // it available to the us, the guest program. This is the only way for us to
+    // access files/dirs on the host filesystem
+    if (builtin.os.tag == .wasi) {
+        // This sets our CWD to "/preopens/cwd"
+        // Dot-prefixed preopens like `--dir=.` are "mounted" at "/preopens/cwd"
+        // Other preopens like `--dir=lib` are "mounted" at "/"
+        try std.os.initPreopensWasi(std.heap.page_allocator, "/preopens/cwd");
+    }
+
     return mainArgs(gpa, arena, args);
 }