[engine] Include arguments in emit errors

This will make debugging slightly easier when encountering these errors.

Change-Id: Ie9c671889c715dd64fb045aed057d451c437cd13
Reviewed-on: https://fuchsia-review.googlesource.com/c/shac-project/shac/+/931036
Fuchsia-Auto-Submit: Oliver Newman <olivernewman@google.com>
Reviewed-by: Ina Huh <ihuh@google.com>
Commit-Queue: Oliver Newman <olivernewman@google.com>

internal/engine/run_test.go

@@ -1528,7 +1528,7 @@ func TestTestDataFailOrThrow(t *testing.T) {
 		},
 		{
 			"ctx-emit-finding-end_col-col-equal.star",
-			"ctx.emit.finding: for parameter \"end_col\": must be greater than \"col\"",
+			"ctx.emit.finding: for parameter \"end_col\": \"end_col\" (2) must be greater than \"col\" (2)",
 			"  //ctx-emit-finding-end_col-col-equal.star:16:21: in cb\n",
 		},
 		{
@@ -1543,7 +1543,7 @@ func TestTestDataFailOrThrow(t *testing.T) {
 		},
 		{
 			"ctx-emit-finding-end_line-line-reverse.star",
-			"ctx.emit.finding: for parameter \"end_line\": must be greater than or equal to \"line\"",
+			"ctx.emit.finding: for parameter \"end_line\": \"end_line\" (1) must be greater than or equal to \"line\" (2)",
 			"  //ctx-emit-finding-end_line-line-reverse.star:16:21: in cb\n",
 		},
 		{

internal/engine/runtime_ctx_emit.go

@@ -87,9 +87,9 @@ func ctxEmitFinding(ctx context.Context, s *shacState, name string, args starlar
 		}
 		if span.End.Line > 0 {
 			if span.End.Line < span.Start.Line {
-				return errors.New("for parameter \"end_line\": must be greater than or equal to \"line\"")
+				return fmt.Errorf("for parameter \"end_line\": \"end_line\" (%d) must be greater than or equal to \"line\" (%d)", span.End.Line, span.Start.Line)
 			} else if span.End.Line == span.Start.Line && span.End.Col > 0 && span.End.Col <= span.Start.Col {
-				return errors.New("for parameter \"end_col\": must be greater than \"col\"")
+				return fmt.Errorf("for parameter \"end_col\": \"end_col\" (%d) must be greater than \"col\" (%d)", span.End.Col, span.Start.Col)
 			}
 		} else if span.End.Col > 0 {
 			// If end_col is set but end_line is unset, assume that end_line is