Add async I/O, SentencePiece, NN, and tensor utilities for ModernBERT support and update Bazel build configuration.

tools/BUILD.bazel

@@ -0,0 +1,7 @@
+load("@rules_python//python:py_library.bzl", "py_library")
+
+py_library(
+    name = "zml_utils",
+    srcs = ["zml_utils.py"],
+    visibility = ["//visibility:public"],
+)

zml/aio.zig

@@ -574,6 +574,58 @@ pub fn unloadBuffers(model: anytype) void {
     }).cb, {}, model);
 }
 
+/// Assists in debuggigng `BufferNotFound` error
+/// This is useful when a buffer key is not found and you want to identify possible alternatives (or typos)
+fn findSimilarBufferKeys(original_key: []const u8, store: BufferStore, temp_allocator: std.mem.Allocator) void {
+    const suffixes = [_][]const u8{ "", ".weight", ".bias" };
+    var shown_keys = std.StringHashMap(void).init(temp_allocator);
+    defer shown_keys.deinit();
+
+    // remove suffix .weight and .bias
+    var base_key = original_key;
+    for (suffixes) |suffix| {
+        if (std.mem.endsWith(u8, original_key, suffix)) {
+            base_key = original_key[0 .. original_key.len - suffix.len];
+            break;
+        }
+    }
+
+    // first test: look for exact matches
+    var matches: usize = 0;
+    var it = store.buffers.iterator();
+    while (it.next()) |entry| {
+        const key = entry.key_ptr.*;
+        if (std.mem.startsWith(u8, key, base_key)) {
+            if (matches == 0) log.warn("Similar buffers found:", .{});
+            if (!shown_keys.contains(key)) {
+                log.warn("  - {s}: {}", .{ key, entry.value_ptr.*.shape() });
+                shown_keys.put(key, {}) catch continue;
+                matches += 1;
+            }
+        }
+    }
+
+    // second test: progressive partial matches
+    if (matches == 0) {
+        var components = std.mem.splitScalar(u8, base_key, '.');
+        while (components.next()) |component| {
+            matches = 0;
+            it = store.buffers.iterator();
+            while (it.next()) |entry| {
+                const key = entry.key_ptr.*;
+                if (std.mem.indexOf(u8, key, component) != null and !shown_keys.contains(key)) {
+                    if (matches == 0) log.warn("Partial matches for '{s}':", .{component});
+                    log.warn("  - {s}: {}", .{ key, entry.value_ptr.*.shape() });
+                    shown_keys.put(key, {}) catch continue;
+                    matches += 1;
+                    if (matches >= 5) break;
+                }
+            }
+            if (matches > 0) break;
+        }
+    }
+}
+
 /// deinit all buffers in the given struct
 pub fn awaitAll(buffers: anytype) !void {
     // TODO: implement once we have async buffers.
@@ -600,6 +652,10 @@ fn visitStructAndLoadBuffer(allocator: std.mem.Allocator, prefix_builder: *Prefi
             buf_with_metadata._shape = obj._shape;
             obj.* = try zml.Buffer.from(platform, buf_with_metadata);
         } else {
+            log.err("Buffer not found: {s}", .{prefix});
+
+            findSimilarBufferKeys(prefix, buffer_store, allocator);
+
             return error.BufferNotFound;
         };
     } else if (T == zml.Shape) return;

zml/aio/sentencepiece.zig

@@ -31,6 +31,7 @@ pub fn normalizerFromSpec(spec: sentencepiece_proto.NormalizerSpec) Normalizer {
             .add_dummy_suffix = false,
             .lower_case_ascii = false,
             .split_on_punct_ascii = false,
+            .use_nfc = false,
         },
         if (spec.escape_whitespaces orelse false) Normalizer.sentencepiece_space else null,
     );

zml/nn.zig

@@ -69,15 +69,15 @@ pub const Activation = union(enum) {
             .leakyReLU => |slope| x.leakyReLU(slope),
         };
     }
-
-    pub fn elu(x: Tensor, alpha: f32) Tensor {
-        return x.cmp(.GE, Tensor.scalar(0, x.dtype())).select(
-            x,
-            x.exp().addConstant(-1).scale(alpha),
-        );
-    }
 };
 
+pub fn elu(x: Tensor, alpha: f32) Tensor {
+    return x.cmp(.GE, Tensor.scalar(0, x.dtype())).select(
+        x,
+        x.exp().addConstant(-1).scale(alpha),
+    );
+}
+
 pub fn chainModules(module_list: anytype, input: Tensor) Tensor {
     const T = @TypeOf(module_list);
     switch (@typeInfo(T)) {
@@ -765,8 +765,7 @@ pub fn sdpa(q_: Tensor, k_: Tensor, v_: Tensor, opts: SdpaOpts) Tensor {
     k = k.mul(head_scaling.convert(k.dtype()));
 
     var attn_weights = q.dot(k, .{.hd});
-    // log.debug("attn_weights : {}", .{attn_weights});
-    // log.debug("attn_mask : {?}", .{attn_mask});
+    // log.debug("attn_weights : {}, attn_mask : {?}", .{ attn_weights, attn_mask });
     if (attn_mask) |mask| attn_weights = attn_weights.add(mask.broad(attn_weights.shape()));
     attn_weights = attn_weights.convert(.f32).softmax(.k).convert(q.dtype());
 

zml/tensor.zig

@@ -1262,8 +1262,15 @@ pub const Tensor = struct {
     /// Returns a Tensor containing the softmax function applied to each element of the input Tensor.
     pub fn softmax(self: Tensor, axis_: anytype) Tensor {
         const a = self.axis(axis_);
+        const max_val = self.max(a);
+        const row_mask = max_val.cmp(.GT, Tensor.scalar(-std.math.inf(f64), self.dtype()));
+
         const exp_diff_max = self.sub(self.max(a).broad(self._shape)).exp();
-        return exp_diff_max.div(exp_diff_max.sum(a).broad(self._shape));
+        const res = exp_diff_max.div(exp_diff_max.sum(a).broad(self._shape));
+
+        // If a row is full -inf return full 0 instead of full nan,
+        // this fix attention when mask hides a full row.
+        return row_mask.broad(self.shape()).select(res, Tensor.scalar(0, self.dtype()));
     }
 
     /// Returns a Tensor containing the log of the sum of exponential over the given axis.