read streams: remove probeFile

The API was strange. It is now clearer to have the logic in its own
block.

Author: motiejus

src/main.zig

@@ -661,52 +661,6 @@ fn optionalStringEnvVar(arena: Allocator, name: []const u8) !?[]const u8 {
     }
 }
 
-const FileType = union(enum) {
-    regular,
-    stream: struct {
-        handle: std.os.fd_t,
-        should_close_fd: bool,
-    },
-};
-
-// probeFile checks if the file is regular or a stream. If it is a stream, it
-// will return its file descriptor (open for reading) along with instruction
-// whether the caller should close the fd when done.
-fn probeFile(name: []const u8) !FileType {
-    if (mem.eql(u8, name, "-"))
-        return FileType{
-            .stream = .{
-                .handle = io.getStdIn().handle,
-                .should_close_fd = false,
-            },
-        };
-
-    // all files are files or directories in windwos. So if it's not stdin,
-    // it's a file.
-    if (builtin.os.tag == .windows)
-        return FileType.regular;
-
-    // we are on POSIX or wasm and need to determine if a given path
-    // is a stream. We have 2 choices here:
-    // 1. open + lseek. If lseek fails, it's a stream. Always 2 syscalls.
-    // 2. fstat + optional open. If fstat tells us it's a file, we return
-    // 'regular'. If it's not a file, we open and return the file descriptor.
-    // One syscall if the file is a regular file, 2 syscalls if it is a stream.
-    // Use the latter.
-
-    var stat_info = try std.os.fstatat(fs.cwd().fd, name, 0);
-    if (stat_info.mode & std.os.S.IFMT == std.os.S.IFREG)
-        return FileType.regular;
-
-    // Not a regular file. Open it and return a file descriptor.
-    return FileType{
-        .stream = .{
-            .handle = try std.os.open(name, std.os.O.RDONLY, 0),
-            .should_close_fd = true,
-        },
-    };
-}
-
 // Read an open file descriptor to a new file in `dst_dir`. Return a file name
 // of the new file.
 fn copyToFile(
@@ -3111,30 +3065,52 @@ fn buildOutputType(
         temp_files_for_comp.deinit();
     }
 
-    // if a c_source_file is not a regular file, dump it to a tempdir.
+    // if a c_source_file is not a regular file, dump it to a tempdir
+    // and replace the src_name with the newly created file.
     // translate-c works fine with streams; other actions don't.
     if (arg_mode != .translate_c) {
-        for (c_source_files.items) |*src| {
+        c_src_loop: for (c_source_files.items) |*src| {
             // optimization: if the file extension is known, assume it is
             // a regular file and keep going. This is in the hot path.
             // If we remove this check, all input files will get an extra
             // syscall or two of overhead.
             if (Compilation.classifyFileExt(src.src_path) != .unknown)
                 continue;
 
-            switch (try probeFile(src.src_path)) {
-                .regular => continue,
-                .stream => |o| {
-                    if (o.should_close_fd)
-                        std.os.close(o.handle);
-                    if (src.ext == null)
-                        fatal("-E or -x is required when reading from a non-regular file", .{});
-
-                    const new_file = try copyToFile(arena, o.handle, local_cache_directory);
-                    try temp_files_for_comp.append(new_file);
-                    src.src_path = new_file;
-                },
-            }
+            // if the extension was not supplied or recognized, bail.
+            if (src.ext == null)
+                fatal("-E or -x is required when reading from a non-regular file", .{});
+
+            var close_fd = true;
+            const fd = blk: {
+                if (mem.eql(u8, src.src_path, "-")) {
+                    close_fd = false;
+                    break :blk io.getStdIn().handle;
+                }
+
+                // all things in a windows filesystem are files or directories.
+                // Therefore, if it is not stdin, it is a file.
+                if (builtin.os.tag == .windows)
+                    continue :c_src_loop;
+
+                // On POSIX or wasm need to determine if a given path is a
+                // stream. 2 choices:
+                // 1. open + lseek. If lseek fails, it is a stream. Always 2
+                //    syscalls.
+                // 2. fstat + optional open. If fstat says it's a file, return
+                //    use it as such. If it is not a file, open and return the
+                //    file descriptor. 1,5 syscall. Use this.
+                var stat_info = try std.os.fstatat(fs.cwd().fd, src.src_path, 0);
+                if (stat_info.mode & std.os.S.IFMT == std.os.S.IFREG)
+                    continue :c_src_loop;
+
+                break :blk try std.os.open(src.src_path, std.os.O.RDONLY, 0);
+            };
+            defer if (close_fd) std.os.close(fd);
+
+            const new_file = try copyToFile(arena, fd, local_cache_directory);
+            try temp_files_for_comp.append(new_file);
+            src.src_path = new_file;
         }
     }