Add comments to FunctionGen

Now we can emit comments which stick to functions instead of coming
before or after the functions when emitting code.

For followup: I think we can simplify FunctionGen and ValidationGen

staging/src/k8s.io/code-generator/cmd/validation-gen/validation.go

@@ -1174,6 +1174,9 @@ func emitCallsToValidators(c *generator.Context, validations []validators.Functi
 			}
 		}
 
+		for _, comment := range v.Comments() {
+			sw.Do("// $.$\n", comment)
+		}
 		if isShortCircuit {
 			sw.Do("if e := ", nil)
 			emitCall()
@@ -1214,11 +1217,15 @@ func (g *genValidations) emitValidationVariables(c *generator.Context, t *types.
 		return cmp.Compare(a.Var().Name, b.Var().Name)
 	})
 	for _, variable := range variables {
-		supportInitFn, supportInitArgs := variable.Init().SignatureAndArgs()
+		fn := variable.Init()
+		supportInitFn, supportInitArgs := fn.SignatureAndArgs()
 		targs := generator.Args{
 			"varName": c.Universe.Type(types.Name(variable.Var())),
 			"initFn":  c.Universe.Type(supportInitFn),
 		}
+		for _, comment := range fn.Comments() {
+			sw.Do("// $.$\n", comment)
+		}
 		sw.Do("var $.varName|private$ = $.initFn|raw$", targs)
 		typeArgs := variable.Init().TypeArgs()
 		if len(typeArgs) > 0 {
@@ -1277,6 +1284,9 @@ func toGolangSourceDataLiteral(sw *generator.SnippetWriter, c *generator.Context
 			targs := generator.Args{
 				"funcName": c.Universe.Type(fn),
 			}
+			for _, comment := range v.Function.Comments() {
+				sw.Do("// $.$\n", comment)
+			}
 			sw.Do("$.funcName|raw$", targs)
 		} else {
 			// If the function to be wrapped has additional arguments, we need

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/validators.go

@@ -302,6 +302,10 @@ type FunctionGen interface {
 	// Conditions returns the conditions that must true for a resource to be
 	// validated by this function.
 	Conditions() Conditions
+
+	// Comments returns optional comments that should be added to the generated
+	// code (without the leading "//").
+	Comments() []string
 }
 
 // Conditions defines what conditions must be true for a resource to be validated.
@@ -356,14 +360,34 @@ func GenericFunction(tagName string, flags FunctionFlags, function types.Name, t
 	return &functionGen{tagName: tagName, flags: flags, function: function, extraArgs: anyArgs, typeArgs: typeArgs}
 }
 
+// WithCondition adds a condition to a FunctionGen.
 func WithCondition(fn FunctionGen, conditions Conditions) FunctionGen {
 	name, args := fn.SignatureAndArgs()
 	return &functionGen{
-		tagName: fn.TagName(), flags: fn.Flags(), function: name, extraArgs: args, typeArgs: fn.TypeArgs(),
+		tagName:    fn.TagName(),
+		flags:      fn.Flags(),
+		function:   name,
+		extraArgs:  args,
+		typeArgs:   fn.TypeArgs(),
+		comments:   fn.Comments(),
 		conditions: conditions,
 	}
 }
 
+// WithComment adds a comment to a FunctionGen.
+func WithComment(fn FunctionGen, comment string) FunctionGen {
+	name, args := fn.SignatureAndArgs()
+	return &functionGen{
+		tagName:    fn.TagName(),
+		flags:      fn.Flags(),
+		function:   name,
+		extraArgs:  args,
+		typeArgs:   fn.TypeArgs(),
+		comments:   append(fn.Comments(), comment),
+		conditions: fn.Conditions(),
+	}
+}
+
 type functionGen struct {
 	tagName    string
 	function   types.Name
@@ -371,6 +395,7 @@ type functionGen struct {
 	typeArgs   []types.Name
 	flags      FunctionFlags
 	conditions Conditions
+	comments   []string
 }
 
 func (v *functionGen) TagName() string {
@@ -389,6 +414,8 @@ func (v *functionGen) Flags() FunctionFlags {
 
 func (v *functionGen) Conditions() Conditions { return v.conditions }
 
+func (v *functionGen) Comments() []string { return v.comments }
+
 // Variable creates a VariableGen for a given function name and extraArgs.
 func Variable(variable PrivateVar, init FunctionGen) VariableGen {
 	return &variableGen{