Add utility functions for getting FunctionInputs and FunctionOutputs.

Author: smowton

ql/src/semmle/go/dataflow/FunctionInputsAndOutputs.qll

@@ -51,6 +51,20 @@ class FunctionInput extends TFunctionInput {
   abstract string toString();
 }
 
+module FunctionInput {
+  /** Gets a `FunctionInput` representing the `i`th parameter. */
+  FunctionInput parameter(int i) { result.isParameter(i) }
+
+  /** Gets a `FunctionInput` representing the receiver. */
+  FunctionInput receiver() { result.isReceiver() }
+
+  /** Gets a `FunctionInput` representing the result of a single-result function. */
+  FunctionInput functionResult() { result.isResult() }
+
+  /** Gets a `FunctionInput` representing the `i`th result. */
+  FunctionInput functionResult(int i) { result.isParameter(i) }
+}
+
 /** A parameter position of a function, viewed as a source of input. */
 private class ParameterInput extends FunctionInput, TInParameter {
   int index;
@@ -172,6 +186,20 @@ class FunctionOutput extends TFunctionOutput {
   abstract string toString();
 }
 
+module FunctionOutput {
+  /** Gets a `FunctionOutput` representing the result of a single-result function. */
+  FunctionOutput functionResult() { result.isResult() }
+
+  /** Gets a `FunctionOutput` representing the `i`th result. */
+  FunctionOutput functionResult(int i) { result.isParameter(i) }
+
+  /** Gets a `FunctionOutput` representing the receiver after a function returns. */
+  FunctionOutput receiver() { result.isReceiver() }
+
+  /** Gets a `FunctionOutput` representing the `i`th parameter after a function returns. */
+  FunctionOutput parameter(int i) { result.isParameter(i) }
+}
+
 /** A result position of a function, viewed as an output. */
 private class OutResult extends FunctionOutput, TOutResult {
   int index;

ql/src/semmle/go/frameworks/Echo.qll

@@ -68,7 +68,7 @@ private module Echo {
       exists(DataFlow::MethodCallNode call |
         call.getTarget().hasQualifiedName(packagePath(), "Context", "Bind")
       |
-        this = any(FunctionOutput output | output.isParameter(0)).getExitNode(call)
+        this = FunctionOutput::parameter(0).getExitNode(call)
       )
     }
   }

ql/src/semmle/go/frameworks/Gin.qll

@@ -128,7 +128,7 @@ private module Gin {
             methodName = "ShouldBindYAML"
           )
         |
-          this = any(FunctionOutput output | output.isParameter(0)).getExitNode(call)
+          this = FunctionOutput::parameter(0).getExitNode(call)
         )
       )
     }

ql/src/semmle/go/frameworks/HTTP.qll

@@ -37,7 +37,7 @@ private module GoRestfulHttp {
             .getTarget()
             .hasQualifiedName(package("github.com/emicklei/go-restful", ""), "Request", "ReadEntity")
       |
-        this = any(FunctionOutput output | output.isParameter(0)).getExitNode(call)
+        this = FunctionOutput::parameter(0).getExitNode(call)
       )
     }
   }