Simplistic argument checking

To be expanded when optional arguments arrive.

testdata/bad_function_call.golden

@@ -0,0 +1 @@
+RUNTIME ERROR: function expected 1 argument(s), but got 0

testdata/bad_function_call.jsonnet

@@ -0,0 +1 @@
+(function(x) x)()

testdata/bad_function_call2.golden

@@ -0,0 +1 @@
+RUNTIME ERROR: function expected 1 argument(s), but got 2

testdata/bad_function_call2.jsonnet

@@ -0,0 +1 @@
+(function(x) x)(1, 2)

testdata/bad_function_call_and_error.golden

@@ -0,0 +1 @@
+RUNTIME ERROR: function expected 1 argument(s), but got 2

testdata/bad_function_call_and_error.jsonnet

@@ -0,0 +1 @@
+(function(x) x)(error "x", error "y")

thunks.go

@@ -80,7 +80,10 @@ func makeCallThunk(ec evalCallable, args callArguments) potentialValue {
 
 func (th *callThunk) getValue(i *interpreter, trace *TraceElement) (value, error) {
 	evaluator := makeEvaluator(i, trace)
-	// TODO(sbarzowski): actually this trace is kinda useless inside...
+	err := checkArguments(evaluator, th.args, th.function.Parameters())
+	if err != nil {
+		return nil, err
+	}
 	return th.function.EvalCall(th.args, evaluator)
 }
 

value.go

@@ -244,6 +244,16 @@ func (f *valueFunction) parameters() ast.Identifiers {
 	return f.ec.Parameters()
 }
 
+func checkArguments(e *evaluator, args callArguments, params ast.Identifiers) error {
+	// TODO(sbarzowski) this will get much more complicated with named params
+	numPassed := len(args.positional)
+	numExpected := len(params)
+	if numPassed != numExpected {
+		return e.Error(fmt.Sprintf("function expected %v argument(s), but got %v", numExpected, numPassed))
+	}
+	return nil
+}
+
 func (f *valueFunction) typename() string {
 	return "function"
 }