From 1708da2c710bd5fa84167ed4abc7ec79438c9be4 Mon Sep 17 00:00:00 2001
From: Kendall Condon <goon.pri.low@gmail.com>
Date: Sun, 22 Mar 2026 18:00:51 -0400
Subject: [PATCH] libfuzzer: fix SkipZigTest with new inputs

It is now ignored for inputs from the corpus to ensure the filesystem
and process corpus stay in sync. For other (nondeterministic) inputs the
input builder is now reset.
---
 lib/fuzzer.zig | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/lib/fuzzer.zig b/lib/fuzzer.zig
index 742bf39125..fb5f6dc13f 100644
--- a/lib/fuzzer.zig
+++ b/lib/fuzzer.zig
@@ -594,6 +594,21 @@ const Fuzzer = struct {
                 b.smithed_len = 4;
                 return input;
             }
+
+            pub fn reset(b: *Builder) void {
+                const uid_slices = b.uid_slices.entries.slice();
+                for (uid_slices.items(.key), uid_slices.items(.value)) |uid, *uid_data| {
+                    switch (uid.kind) {
+                        .int => uid_data.ints.deinit(gpa),
+                        .bytes => uid_data.bytes.deinit(gpa),
+                    }
+                }
+                b.uid_slices.clearRetainingCapacity();
+                b.total_ints = 0;
+                b.total_bytes = 0;
+                b.weighted_len = 0;
+                b.smithed_len = 4;
+            }
         };
     };
 
@@ -876,7 +891,14 @@ const Fuzzer = struct {
         // * The test has changed and a previous corpus input is being used
         // * An input provided by the test results in it
         // * The test is non-deterministic
-        if (f.runBytes(bytes, .bytes_fresh)) return;
+        if (f.runBytes(bytes, .bytes_fresh) and
+            modify_fs_corpus // The input is not from the filesystem.
+            // This is required to ensure the filesystem and process corpus are the same.
+        ) {
+            f.input_builder.reset();
+            f.corpus_pos = @enumFromInt(0);
+            return;
+        }
         f.req_values = f.input_builder.total_ints + f.input_builder.total_bytes;
         f.req_bytes = @intCast(f.input_builder.bytes_table.items.len);
         var input = f.input_builder.build();
@@ -1859,7 +1881,6 @@ const MemoryMappedInput = struct {
     /// Invalidates item pointers if more space is required.
     pub fn appendLittleInt(l: *MemoryMappedInput, T: type, x: T) void {
         l.ensureUnusedCapacity(@sizeOf(T));
-        //std.log.debug("{} {} {}", .{ l.writeSlice().len, l.len, @sizeOf(T) });
         l.writeSlice()[4 + l.len ..][0..@sizeOf(T)].* = @bitCast(mem.nativeToLittle(T, x));
         l.len += @sizeOf(T);
         l.writeLen();