From 56571a70d99a896777146e9588d9f6a04124c9a5 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 16 Sep 2026 16:05:26 -0700
Subject: [PATCH] std.Build.Cache: fix flagsAndPath implementation

it was scanning for sentinel starting from flags rather than flags + 1,
which could lead to the scenario where the path is empty because flags
is zero
---
 lib/std/Build/Cache.zig | 14 ++++++--------
 src/Compilation.zig     |  2 +-
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/lib/std/Build/Cache.zig b/lib/std/Build/Cache.zig
index 3eaeef3ab92ab88f11c4da1418aa84fb51c960ef..d0a7d93e16b1207429222ee77a96361a345290e4 100644
--- a/lib/std/Build/Cache.zig
+++ b/lib/std/Build/Cache.zig
@@ -499,9 +499,10 @@ pub const Manifest = struct {
             pub fn flagsAndPath(off: File.Offset, contents: []const u8) [:0]const u8 {
                 const flags_off = @offsetOf(File, "flags");
                 comptime assert(@offsetOf(File, "path_start") - flags_off == 1);
-                const hash_start = @backingInt(off) + flags_off;
-                const hash_end = mem.findScalarPos(u8, contents, hash_start, 0).?;
-                return contents[hash_start..hash_end :0];
+                const start = @backingInt(off) + flags_off;
+                // Scan for the sentinel starting from the path_start offset because flags might be zero.
+                const end = mem.findScalarPos(u8, contents, start + 1, 0).?;
+                return contents[start..end :0];
             }
 
             pub fn pathFallible(off: File.Offset, contents: []const u8) error{InvalidFormat}![:0]const u8 {
@@ -898,7 +899,8 @@ pub const Manifest = struct {
         // This is *not* hashing the contents of the input files. It is the
         // flags (including prefix) and path only.
         for (man.files.keys()[0..man.input_paths.items.len]) |file_off| {
-            man.hashFlagsAndPath(file_off, &man.hash.hasher);
+            const flags_and_path = file_off.flagsAndPath(man.contents.items);
+            man.hash.hasher.update(mem.absorbSentinel(flags_and_path));
         }
 
         var input_digest: BinDigest = undefined;
@@ -2288,10 +2290,6 @@ pub const Manifest = struct {
         hasher.update(contents.items[contents_start..][0..contents_len]);
         hasher.final(bin_digest);
     }
-
-    fn hashFlagsAndPath(m: *const Manifest, off: File.Offset, hasher: *Hasher) void {
-        hasher.update(off.flagsAndPath(m.contents.items));
-    }
 };
 
 /// Create/Write a file, close it, then grab its stat.mtime timestamp.
diff --git a/src/Compilation.zig b/src/Compilation.zig
index 5b3131bf8734ffec53c0bfed5fc04d119716b313..d94b7146b59afed2774f83d89b63604794a1ddbd 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -5530,7 +5530,7 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: std.Pr
                     return comp.failCObj(c_object, "checking cache failed: {f}", .{diagnostic.fmt(&man)});
                 },
             };
-            log.debug("C object cache {f}", .{status.fmt(&man)});
+            log.debug("C object {q} cache {f}", .{ c_object.src.src_path, status.fmt(&man) });
             if (status == .hit) break :d man.hitDigestHex();
         }
         var argv: std.array_list.Managed([]const u8) = .init(gpa);
-- 
2.54.0