Set EvalConfig.EvaluationTimestamp to time.Now() if it is empty (zero value), as described in the config comments.

cql.go

@@ -97,12 +97,16 @@ type EvalConfig struct {
 // should not be called from multiple goroutines on a single *ELM.
 // Errors returned by Eval will always be a result.EngineError.
 func (e *ELM) Eval(ctx context.Context, retriever retriever.Retriever, config EvalConfig) (result.Libraries, error) {
+	evalTS := config.EvaluationTimestamp
+	if config.EvaluationTimestamp.IsZero() {
+		evalTS = time.Now()
+	}
 	c := interpreter.Config{
 		DataModels:          e.dataModels,
 		Parameters:          e.parsedParams,
 		Retriever:           retriever,
 		Terminology:         config.Terminology,
-		EvaluationTimestamp: config.EvaluationTimestamp,
+		EvaluationTimestamp: evalTS,
 		ReturnPrivateDefs:   config.ReturnPrivateDefs,
 	}
 

cql_test.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"errors"
 	"testing"
+	"time"
 
 	"github.com/google/cql"
 	"github.com/google/cql/model"
@@ -115,6 +116,40 @@ func TestCQL(t *testing.T) {
 	}
 }
 
+func TestCQL_EvalEmptyTimestamp(t *testing.T) {
+	// This test checks that an empty EvalConfig.EvaluationTimestamp is set to time.Now() at the start
+	// of the eval request. We do this by sanity checking the result of Now() is within 2 mins of the
+	// test assertion time.
+	cqlSources := []string{dedent.Dedent(`
+	library TESTLIB version '1.0.0'
+	define TESTRESULT: Now()`)}
+	parserConfig := cql.ParseConfig{}
+	evalConfig := cql.EvalConfig{}
+
+	elm, err := cql.Parse(context.Background(), cqlSources, parserConfig)
+	if err != nil {
+		t.Fatalf("Parse returned unexpected error: %v", err)
+	}
+
+	results, err := elm.Eval(context.Background(), nil, evalConfig)
+	if err != nil {
+		t.Fatalf("Eval returned unexpected error: %v", err)
+	}
+
+	gotResult := getTESTRESULTWithSources(t, results)
+	dt, err := result.ToDateTime(gotResult)
+	if err != nil {
+		t.Errorf("returned result is not a DateTime, err: %v", err)
+	}
+
+	// Check that the dt is within [time.Now()-2min, time.Now()]
+	end := time.Now()
+	start := end.Add(-2 * time.Minute)
+	if dt.Date.Before(start) || dt.Date.After(end) {
+		t.Errorf("returned CQL Now() result is not within 2 mins of time.Now()")
+	}
+}
+
 func TestCQL_ParseErrors(t *testing.T) {
 	tests := []struct {
 		name         string