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Co-authored-by: Noah Treuhaft <[email protected]>

compiler/kernel/groupby.go

@@ -45,7 +45,7 @@ func (b *Builder) compileAggAssignment(assignment dag.Assignment) (field.Path, *
 	}
 	this, ok := assignment.LHS.(*dag.This)
 	if !ok {
-		return nil, nil, errors.New("internal error: aggregator assignment LHS must be a static path")
+		return nil, nil, errors.New("internal error: aggregator assignment LHS is not a static path: %#v", assignment.LHS)
 	}
 	m, err := b.compileAgg(aggAST)
 	return this.Path, m, err

compiler/semantic/op.go

@@ -416,7 +416,7 @@ func (a *analyzer) semOp(o ast.Op, seq dag.Seq) (dag.Seq, error) {
 			return nil, err
 		}
 		if assignmentHasDynamicLHS(keys) {
-			return nil, errors.New("summarize: keys must be static field references")
+			return nil, errors.New("summarize: key output fields must be static")
 		}
 		if len(keys) == 0 && len(o.Aggs) == 1 {
 			if seq := a.singletonAgg(o.Aggs[0], seq); seq != nil {
@@ -428,7 +428,7 @@ func (a *analyzer) semOp(o ast.Op, seq dag.Seq) (dag.Seq, error) {
 			return nil, err
 		}
 		if assignmentHasDynamicLHS(aggs) {
-			return nil, errors.New("summarize: aggs must be static field references")
+			return nil, errors.New("summarize: aggregate output field must be static")
 		}
 		// Note: InputSortDir is copied in here but it's not meaningful
 		// coming from a parser AST, only from a worker using the kernel DSL,
@@ -967,8 +967,6 @@ func (a *analyzer) semOpAssignment(p *ast.OpAssignment) (dag.Op, error) {
 	var aggs, puts []dag.Assignment
 	for _, assign := range p.Assignments {
 		// Parition assignments into agg vs. puts.
-		// It's okay to pass false here for the summarize bool because
-		// semAssignment will check if the RHS is a dag.Agg and override.
 		a, err := a.semAssignment(assign)
 		if err != nil {
 			return nil, err