[MetaSchedule] Handle deserializing empty string RVs in trace

src/tir/schedule/trace.cc

@@ -153,7 +153,7 @@ Array<ObjectRef> TranslateInputRVs(const Array<ObjectRef>& inputs,
     const char* name = str->data;
     int64_t size = str->size;
     // Case 2. string
-    if (size > 2 && name[0] == '"' && name[size - 1] == '"') {
+    if (size >= 2 && name[0] == '"' && name[size - 1] == '"') {
       results.push_back(String(std::string(name + 1, size - 2)));
       continue;
     }

tests/python/unittest/test_tir_schedule_trace.py

@@ -101,6 +101,15 @@ def _make_enter_postproc():
     )
 
 
+def _make_annotate(block: BlockRV, annotation: str):
+    return Instruction(
+        kind=InstructionKind.get("Annotate"),
+        inputs=[block, annotation],
+        attrs=["meta_schedule.auto_tensorize"],
+        outputs=[],
+    )
+
+
 def _make_trace_1(b0, l1, l2):  # pylint: disable=invalid-name
     return Trace(
         insts=[
@@ -275,5 +284,53 @@ def test_apply_json_to_schedule_1():
     tvm.ir.assert_structural_equal(elementwise_inlined, sch.mod["main"])
 
 
+def _test_apply_annotation_trace_from_json(annotation: str):
+    """Test applying an annotation works without crashing.
+
+    Designed to handle some previously failing edge cases like the
+    empty string.
+    """
+    b0 = BlockRV()
+    trace = Trace(
+        insts=[
+            _make_get_block(name="B", output=b0),
+            _make_annotate(block=b0, annotation=annotation),
+        ],
+        decisions={},
+    )
+    json_obj = trace.as_json()
+    sch = tir.Schedule(elementwise, debug_mask="all")
+    Trace.apply_json_to_schedule(json_obj, sch)
+
+    @T.prim_func
+    def elementwise_expected(a: T.handle, c: T.handle) -> None:
+        A = T.match_buffer(a, (128, 128))
+        B = T.alloc_buffer((128, 128))
+        C = T.match_buffer(c, (128, 128))
+        for i, j in T.grid(128, 128):
+            with T.block("B"):
+                T.block_attr({"meta_schedule.auto_tensorize":annotation})
+                vi, vj = T.axis.remap("SS", [i, j])
+                B[vi, vj] = A[vi, vj] * 2.0
+        for i, j in T.grid(128, 128):
+            with T.block("C"):
+                vi, vj = T.axis.remap("SS", [i, j])
+                C[vi, vj] = B[vi, vj] + 1.0
+
+    tvm.ir.assert_structural_equal(elementwise_expected, sch.mod["main"])
+
+def test_apply_annotation_from_json():
+    # Something reasonable
+    _test_apply_annotation_trace_from_json("SSRSSR")
+
+    # The empty string
+    _test_apply_annotation_trace_from_json("")
+
+    # A string of two quotation marks
+    _test_apply_annotation_trace_from_json('""')
+
+    # A string of one quotation mark
+    _test_apply_annotation_trace_from_json('"')
+
 if __name__ == "__main__":
     tvm.testing.main()