[Impeller] added static check that fragment shader and vertex shaders slots match

impeller/renderer/pipeline.h

@@ -87,8 +87,73 @@ PipelineFuture<ComputePipelineDescriptor> CreatePipelineFuture(
     const Context& context,
     std::optional<ComputePipelineDescriptor> desc);
 
+/// This is a classed use to check that the input slots of fragment shaders
+/// match the output slots of the vertex shaders.
+/// It's not used at runtime.
+template <typename VertexShaderT, typename FragmentShaderT>
+class ShaderBindingComparator {
+ public:
+  static constexpr bool CompileTimeStrEqual(const char* str1,
+                                            const char* str2) {
+    return *str1 == *str2 &&
+           (*str1 == '\0' || CompileTimeStrEqual(str1 + 1, str2 + 1));
+  }
+
+  static constexpr bool Compare() {
+    constexpr size_t num_outputs = VertexShaderT::kAllShaderStageOutputs.size();
+    constexpr size_t num_inputs = FragmentShaderT::kAllShaderStageInputs.size();
+
+    if (num_inputs > num_outputs) {
+      return false;
+    }
+
+    for (size_t i = 0; i < num_inputs; ++i) {
+      const ShaderStageIOSlot* input_slot =
+          FragmentShaderT::kAllShaderStageInputs[i];
+      for (size_t j = 0; j < num_outputs; ++j) {
+        const ShaderStageIOSlot* output_slot =
+            VertexShaderT::kAllShaderStageOutputs[j];
+        if (input_slot->location == output_slot->location) {
+          if (!CompileTimeStrEqual(input_slot->name, output_slot->name) ||
+              input_slot->set != output_slot->set ||
+              input_slot->binding != output_slot->binding ||
+              input_slot->type != output_slot->type ||
+              input_slot->bit_width != output_slot->bit_width ||
+              input_slot->vec_size != output_slot->vec_size ||
+              input_slot->columns != output_slot->columns ||
+              input_slot->offset != output_slot->offset) {
+            return false;
+          }
+        }
+      }
+    }
+
+    return true;
+  }
+};
+
+// The following shaders don't define output slots.
+// TODO(tbd): Make impellerc emit an empty array for output slots.
+struct CheckerboardVertexShader;
+struct ClipVertexShader;
+
+template <typename FragmentShaderT>
+class ShaderBindingComparator<CheckerboardVertexShader, FragmentShaderT> {
+ public:
+  static constexpr bool Compare() { return true; }
+};
+
+template <typename FragmentShaderT>
+class ShaderBindingComparator<ClipVertexShader, FragmentShaderT> {
+ public:
+  static constexpr bool Compare() { return true; }
+};
+
 template <class VertexShader_, class FragmentShader_>
 class RenderPipelineT {
+  static_assert(
+      ShaderBindingComparator<VertexShader_, FragmentShader_>::Compare());
+
  public:
   using VertexShader = VertexShader_;
   using FragmentShader = FragmentShader_;