Start validation;

validate.lua

@@ -0,0 +1,69 @@
+return function(schema, tree)
+
+  local context = {
+    operationNames = {},
+    hasAnonymousOperation = false,
+    typeStack = {}
+  }
+
+  local visitors = {
+    document = function(node)
+      return node.definitions
+    end,
+
+    operation = function(node)
+      local name = node.name and node.name.value
+
+      if name then
+        if context.operationNames[name] then
+          error('Multiple operations exist named "' .. name .. '"')
+        else
+          context.operationNames[name] = true
+        end
+      else
+        if context.hasAnonymousOperation or next(context.operationNames) then
+          error('Cannot have more than one operation when using anonymous operations')
+        end
+
+        context.hasAnonymousOperation = true
+      end
+
+      return {node.selectionSet}
+    end,
+
+    selectionSet = function(node)
+      return node.selections
+    end,
+
+    field = function(node)
+      if context.typeStack[#context.typeStack].__type == 'Scalar' and node.selectionSet then
+        error('Scalar values cannot have selections')
+      end
+
+      if node.selectionSet then
+        return {node.selectionSet}
+      end
+    end
+  }
+
+  local root = schema.query
+  local function visit(node)
+    if node.kind and visitors[node.kind] then
+      if node.kind == 'operation' then
+        table.insert(context.typeStack, schema.query)
+      elseif node.kind == 'field' then
+        local parent = context.typeStack[#context.typeStack]
+        table.insert(context.typeStack, parent.fields[node.name.value].kind)
+      end
+
+      local targets = visitors[node.kind](node)
+      if targets then
+        for _, target in ipairs(targets) do
+          visit(target)
+        end
+      end
+    end
+  end
+
+  visit(tree)
+end