webgl: fix 'Gather' with 0-rank indices

lib/backends/webgl/ops/gather.ts

@@ -16,10 +16,6 @@ export class WebGLGather extends Gather implements WebGLOperator {
     const indexDataShape = inputs[1].dims.slice();
     const outputShape = new Array(inputShape.length + indexDataShape.length - 1);
 
-    if (outputShape.length === 0) {
-      throw Error('A scalar tensor output has not been supported');
-    }
-
     const axis = ShapeUtil.normalizeAxis(this.axis, inputShape.length);
     const indexCopyOps: string[] = [];
     for (let i = 0; i < outputShape.length; i++) {
@@ -42,13 +38,14 @@ export class WebGLGather extends Gather implements WebGLOperator {
       }
     }
 
-    const orank = outputShape.length;
+    const orank = outputShape.length || 1;
     const irank = inputShape.length;
-    const iDrank = indexDataShape.length;
+    const iDrank = indexDataShape.length || 1;
     const shaderSource = `
       float process(int outputIdx[${orank}]) {
         int inputIdx[${irank}];
         int indexDataIdx[${iDrank}];
+        indexDataIdx[0] = 0;
         ${indexCopyOps.join('\n        ')}
         int idx = int(_B(indexDataIdx));
         inputIdx[${axis}] = idx < 0 ? idx + ${inputShape[axis]} : idx;

test/data/ops/gather.jsonc

@@ -0,0 +1,97 @@
+[
+  {
+    "name": "Gather",
+    "operator": "Gather",
+    "attributes": [],
+    "cases": [
+      {
+        "name": "data[4] indices[]",
+        "inputs": [
+          {
+            "data": [1, 2, 3, 4],
+            "dims": [4],
+            "type": "float32"
+          },
+          {
+            "data": [1],
+            "dims": [],
+            "type": "int32"
+          }
+        ],
+        "outputs": [
+          {
+            "data": [2],
+            "dims": [],
+            "type": "float32"
+          }
+        ]
+      },
+      {
+        "name": "data[4] indices[1]",
+        "inputs": [
+          {
+            "data": [1, 2, 3, 4],
+            "dims": [4],
+            "type": "float32"
+          },
+          {
+            "data": [1],
+            "dims": [1],
+            "type": "int32"
+          }
+        ],
+        "outputs": [
+          {
+            "data": [2],
+            "dims": [1],
+            "type": "float32"
+          }
+        ]
+      },
+      {
+        "name": "data[2,4] indices[]",
+        "inputs": [
+          {
+            "data": [1, 2, 3, 4, 5, 6, 7, 8],
+            "dims": [2, 4],
+            "type": "float32"
+          },
+          {
+            "data": [1],
+            "dims": [],
+            "type": "int32"
+          }
+        ],
+        "outputs": [
+          {
+            "data": [5, 6, 7, 8],
+            "dims": [4],
+            "type": "float32"
+          }
+        ]
+      },
+      {
+        "name": "data[2,4] indices[1]",
+        "inputs": [
+          {
+            "data": [1, 2, 3, 4, 5, 6, 7, 8],
+            "dims": [2, 4],
+            "type": "float32"
+          },
+          {
+            "data": [1],
+            "dims": [1],
+            "type": "int32"
+          }
+        ],
+        "outputs": [
+          {
+            "data": [5, 6, 7, 8],
+            "dims": [1, 4],
+            "type": "float32"
+          }
+        ]
+      }
+    ]
+  }
+]