Fix another test failure, small cleanups

lib/std/process.zig

@@ -312,11 +312,15 @@ pub fn ArgIteratorGeneral(comptime options: ArgIteratorGeneralOptions) type {
         allocator: Allocator,
         index: usize = 0,
         cmd_line: []const u8,
+
+        /// Should the cmd_line field be free'd (using the allocator) on deinit()?
         free_cmd_line_on_deinit: bool,
 
+        /// buffer MUST be long enough to hold the cmd_line plus a null terminator.
+        /// buffer will we free'd (using the allocator) on deinit()
+        buffer: []u8,
         start: usize = 0,
         end: usize = 0,
-        buffer: []u8,
 
         pub const Self = @This();
 
@@ -336,6 +340,19 @@ pub fn ArgIteratorGeneral(comptime options: ArgIteratorGeneralOptions) type {
             };
         }
 
+        /// cmd_line_utf8 will be free'd (with the allocator) on deinit()
+        pub fn initTakeOwnership(allocator: Allocator, cmd_line_utf8: []const u8) InitError!Self {
+            var buffer = try allocator.alloc(u8, cmd_line_utf8.len + 1);
+            errdefer allocator.free(buffer);
+
+            return Self{
+                .allocator = allocator,
+                .cmd_line = cmd_line_utf8,
+                .free_cmd_line_on_deinit = true,
+                .buffer = buffer,
+            };
+        }
+
         /// cmd_line_utf16le MUST be encoded UTF16-LE, and is converted to UTF-8 in an internal buffer
         pub fn initUtf16le(allocator: Allocator, cmd_line_utf16le: [*:0]const u16) InitUtf16leError!Self {
             var utf16le_slice = cmd_line_utf16le[0..mem.len(cmd_line_utf16le)];

src/main.zig

@@ -4095,25 +4095,18 @@ pub const ClangArgIterator = struct {
         var response_file = try fs.cwd().openFile(resp_file_path, .{
             .read = true,
         });
-        var cmd_line_len = try response_file.getEndPos();
+        const cmd_line_len = try response_file.getEndPos();
 
-        if (cmd_line_len >= std.math.maxInt(usize))
+        // Size of ResponseFile and an additional null terminator must fit in a usize
+        if (cmd_line_len >= (std.math.maxInt(usize) - 1))
             return error.ResponseFileTooLarge;
 
         var cmd_line = try allocator.alloc(u8, @intCast(usize, cmd_line_len));
         errdefer allocator.free(cmd_line);
 
-        cmd_line_len = try response_file.readAll(cmd_line);
+        const cmd_line_read_len = try response_file.readAll(cmd_line);
 
-        var buffer = try allocator.alloc(u8, cmd_line_len + 1);
-        errdefer allocator.free(buffer);
-
-        return ArgIteratorResponseFile{
-            .allocator = allocator,
-            .cmd_line = cmd_line[0..cmd_line_len],
-            .free_cmd_line_on_deinit = true,
-            .buffer = buffer,
-        };
+        return ArgIteratorResponseFile.initTakeOwnership(allocator, cmd_line[0..cmd_line_read_len]);
     }
 
     fn next(self: *ClangArgIterator) !void {