Move rule definitions into own file

rule.go

@@ -0,0 +1,57 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package gas
+
+import (
+	"go/ast"
+	"reflect"
+)
+
+// The Rule interface used by all rules supported by GAS.
+type Rule interface {
+	Match(ast.Node, *Context) (*Issue, error)
+}
+
+// RuleBuilder is used to register a rule definition with the analyzer
+type RuleBuilder func(c Config) (Rule, []ast.Node)
+
+// A RuleSet maps lists of rules to the type of AST node they should be run on.
+// The anaylzer will only invoke rules contained in the list associated with the
+// type of AST node it is currently visiting.
+type RuleSet map[reflect.Type][]Rule
+
+func NewRuleSet() RuleSet {
+	return make(RuleSet)
+}
+
+// Register adds a trigger for the supplied rule for the the
+// specified ast nodes.
+func (r RuleSet) Register(rule Rule, nodes ...ast.Node) {
+	for _, n := range nodes {
+		t := reflect.TypeOf(n)
+		if rules, ok := r[t]; ok {
+			r[t] = append(rules, rule)
+		} else {
+			r[t] = []Rule{rule}
+		}
+	}
+}
+
+// RegisteredFor will return all rules that are registered for a
+// specified ast node.
+func (r RuleSet) RegisteredFor(n ast.Node) []Rule {
+	if rules, found := r[reflect.TypeOf(n)]; found {
+		return rules
+	}
+	return []Rule{}
+}