Support dynamic paths for put and cut op (#4795)

Closes #4555

compiler/kernel/expr.go

@@ -263,15 +263,41 @@ func (b *Builder) compileDotExpr(dot *dag.Dot) (expr.Evaluator, error) {
 	return expr.NewDotExpr(b.zctx(), record, dot.RHS), nil
 }
 
-func compileLval(e dag.Expr) (field.Path, error) {
-	if this, ok := e.(*dag.This); ok {
-		return field.Path(this.Path), nil
+func (b *Builder) compileLval(e dag.Expr) (*expr.Lval, error) {
+	switch e := e.(type) {
+	case *dag.BinaryExpr:
+		if e.Op != "[" {
+			return nil, fmt.Errorf("internal error: invalid lval %#v", e)
+		}
+		lhs, err := b.compileLval(e.LHS)
+		if err != nil {
+			return nil, err
+		}
+		rhs, err := b.compileExpr(e.RHS)
+		if err != nil {
+			return nil, err
+		}
+		lhs.Elems = append(lhs.Elems, expr.NewExprLvalElem(b.zctx(), rhs))
+		return lhs, nil
+	case *dag.Dot:
+		lhs, err := b.compileLval(e.LHS)
+		if err != nil {
+			return nil, err
+		}
+		lhs.Elems = append(lhs.Elems, &expr.StaticLvalElem{Name: e.RHS})
+		return lhs, nil
+	case *dag.This:
+		var elems []expr.LvalElem
+		for _, elem := range e.Path {
+			elems = append(elems, &expr.StaticLvalElem{Name: elem})
+		}
+		return expr.NewLval(elems), nil
 	}
-	return nil, errors.New("invalid expression on lhs of assignment")
+	return nil, fmt.Errorf("internal error: invalid lval %#v", e)
 }
 
 func (b *Builder) compileAssignment(node *dag.Assignment) (expr.Assignment, error) {
-	lhs, err := compileLval(node.LHS)
+	lhs, err := b.compileLval(node.LHS)
 	if err != nil {
 		return expr.Assignment{}, err
 	}

compiler/kernel/groupby.go

@@ -44,12 +44,12 @@ func (b *Builder) compileAggAssignment(assignment dag.Assignment) (field.Path, *
 	if !ok {
 		return nil, nil, errors.New("aggregator is not an aggregation expression")
 	}
-	lhs, err := compileLval(assignment.LHS)
-	if err != nil {
-		return nil, nil, fmt.Errorf("lhs of aggregation: %w", err)
+	this, ok := assignment.LHS.(*dag.This)
+	if !ok {
+		return nil, nil, fmt.Errorf("internal error: aggregator assignment LHS is not a static path: %#v", assignment.LHS)
 	}
 	m, err := b.compileAgg(aggAST)
-	return lhs, m, err
+	return this.Path, m, err
 }
 
 func (b *Builder) compileAgg(agg *dag.Agg) (*expr.Aggregator, error) {

compiler/kernel/op.go

@@ -109,10 +109,7 @@ func (b *Builder) compileLeaf(o dag.Op, parent zbuf.Puller) (zbuf.Puller, error)
 			return nil, err
 		}
 		lhs, rhs := splitAssignments(assignments)
-		cutter, err := expr.NewCutter(b.octx.Zctx, lhs, rhs)
-		if err != nil {
-			return nil, err
-		}
+		cutter := expr.NewCutter(b.octx.Zctx, lhs, rhs)
 		if v.Quiet {
 			cutter.Quiet()
 		}
@@ -174,36 +171,13 @@ func (b *Builder) compileLeaf(o dag.Op, parent zbuf.Puller) (zbuf.Puller, error)
 		if err != nil {
 			return nil, err
 		}
-		putter, err := expr.NewPutter(b.octx.Zctx, clauses)
-		if err != nil {
-			return nil, err
-		}
+		putter := expr.NewPutter(b.octx.Zctx, clauses)
 		return op.NewApplier(b.octx, parent, putter), nil
 	case *dag.Rename:
 		var srcs, dsts field.List
-		for _, fa := range v.Args {
-			dst, err := compileLval(fa.LHS)
-			if err != nil {
-				return nil, err
-			}
-			// We call CompileLval on the RHS because renames are
-			// restricted to dotted field name expressions.
-			src, err := compileLval(fa.RHS)
-			if err != nil {
-				return nil, err
-			}
-			if len(dst) != len(src) {
-				return nil, fmt.Errorf("cannot rename %s to %s", src, dst)
-			}
-			// Check that the prefixes match and, if not, report first place
-			// that they don't.
-			for i := 0; i <= len(src)-2; i++ {
-				if src[i] != dst[i] {
-					return nil, fmt.Errorf("cannot rename %s to %s (differ in %s vs %s)", src, dst, src[i], dst[i])
-				}
-			}
-			dsts = append(dsts, dst)
-			srcs = append(srcs, src)
+		for _, a := range v.Args {
+			dsts = append(dsts, a.LHS.(*dag.This).Path)
+			srcs = append(srcs, a.RHS.(*dag.This).Path)
 		}
 		renamer := expr.NewRenamer(b.octx.Zctx, srcs, dsts)
 		return op.NewApplier(b.octx, parent, renamer), nil
@@ -388,9 +362,9 @@ func (b *Builder) compileAssignments(assignments []dag.Assignment) ([]expr.Assig
 	return keys, nil
 }
 
-func splitAssignments(assignments []expr.Assignment) (field.List, []expr.Evaluator) {
+func splitAssignments(assignments []expr.Assignment) ([]*expr.Lval, []expr.Evaluator) {
 	n := len(assignments)
-	lhs := make(field.List, 0, n)
+	lhs := make([]*expr.Lval, 0, n)
 	rhs := make([]expr.Evaluator, 0, n)
 	for _, a := range assignments {
 		lhs = append(lhs, a.LHS)

compiler/semantic/expr.go

@@ -529,10 +529,10 @@ func (a *analyzer) semExprs(in []ast.Expr) ([]dag.Expr, error) {
 	return exprs, nil
 }
 
-func (a *analyzer) semAssignments(assignments []ast.Assignment, summarize bool) ([]dag.Assignment, error) {
+func (a *analyzer) semAssignments(assignments []ast.Assignment) ([]dag.Assignment, error) {
 	out := make([]dag.Assignment, 0, len(assignments))
 	for _, e := range assignments {
-		a, err := a.semAssignment(e, summarize)
+		a, err := a.semAssignment(e)
 		if err != nil {
 			return nil, err
 		}
@@ -541,64 +541,69 @@ func (a *analyzer) semAssignments(assignments []ast.Assignment, summarize bool)
 	return out, nil
 }
 
-func (a *analyzer) semAssignment(assign ast.Assignment, summarize bool) (dag.Assignment, error) {
+func (a *analyzer) semAssignment(assign ast.Assignment) (dag.Assignment, error) {
 	rhs, err := a.semExpr(assign.RHS)
 	if err != nil {
-		return dag.Assignment{}, fmt.Errorf("rhs of assignment expression: %w", err)
-	}
-	if _, ok := rhs.(*dag.Agg); ok {
-		summarize = true
+		return dag.Assignment{}, fmt.Errorf("right-hand side of assignment: %w", err)
 	}
 	var lhs dag.Expr
-	if assign.LHS != nil {
-		lhs, err = a.semExpr(assign.LHS)
+	if assign.LHS == nil {
+		path, err := deriveLHSPath(rhs)
 		if err != nil {
-			return dag.Assignment{}, fmt.Errorf("lhs of assigment expression: %w", err)
+			return dag.Assignment{}, err
 		}
-	} else if call, ok := assign.RHS.(*ast.Call); ok {
-		path := []string{call.Name}
-		switch call.Name {
+		lhs = &dag.This{Kind: "This", Path: path}
+	} else if lhs, err = a.semExpr(assign.LHS); err != nil {
+		return dag.Assignment{}, fmt.Errorf("left-hand side of assignment: %w", err)
+	}
+	if !isLval(lhs) {
+		return dag.Assignment{}, errors.New("illegal left-hand side of assignment")
+	}
+	if this, ok := lhs.(*dag.This); ok && len(this.Path) == 0 {
+		return dag.Assignment{}, errors.New("cannot assign to 'this'")
+	}
+	return dag.Assignment{Kind: "Assignment", LHS: lhs, RHS: rhs}, nil
+}
+
+func isLval(e dag.Expr) bool {
+	switch e := e.(type) {
+	case *dag.BinaryExpr:
+		return e.Op == "[" && isLval(e.LHS)
+	case *dag.Dot:
+		return isLval(e.LHS)
+	case *dag.This:
+		return true
+	}
+	return false
+}
+
+func deriveLHSPath(rhs dag.Expr) ([]string, error) {
+	var path []string
+	switch rhs := rhs.(type) {
+	case *dag.Call:
+		path = []string{rhs.Name}
+		switch rhs.Name {
 		case "every":
 			// If LHS is nil and the call is every() make the LHS field ts since
 			// field ts assumed with every.
 			path = []string{"ts"}
 		case "quiet":
-			if len(call.Args) > 0 {
-				if p, ok := rhs.(*dag.Call).Args[0].(*dag.This); ok {
-					path = p.Path
+			if len(rhs.Args) > 0 {
+				if this, ok := rhs.Args[0].(*dag.This); ok {
+					path = this.Path
 				}
 			}
 		}
-		lhs = &dag.This{Kind: "This", Path: path}
-	} else if agg, ok := assign.RHS.(*ast.Agg); ok {
-		lhs = &dag.This{Kind: "This", Path: []string{agg.Name}}
-	} else if v, ok := rhs.(*dag.Var); ok {
-		lhs = &dag.This{Kind: "This", Path: []string{v.Name}}
-	} else {
-		lhs, err = a.semExpr(assign.RHS)
-		if err != nil {
-			return dag.Assignment{}, errors.New("assignment name could not be inferred from rhs expression")
-		}
-	}
-	if summarize {
-		// Summarize always outputs its results as new records of "this"
-		// so if we have an "as" that overrides "this", we just
-		// convert it back to a local this.
-		if dot, ok := lhs.(*dag.Dot); ok {
-			if v, ok := dot.LHS.(*dag.Var); ok && v.Name == "this" {
-				lhs = &dag.This{Kind: "This", Path: []string{dot.RHS}}
-			}
-		}
-	}
-	// Make sure we have a valid lval for lhs.
-	this, ok := lhs.(*dag.This)
-	if !ok {
-		return dag.Assignment{}, errors.New("illegal left-hand side of assignment")
-	}
-	if len(this.Path) == 0 {
-		return dag.Assignment{}, errors.New("cannot assign to 'this'")
+	case *dag.Agg:
+		path = []string{rhs.Name}
+	case *dag.Var:
+		path = []string{rhs.Name}
+	case *dag.This:
+		path = rhs.Path
+	default:
+		return nil, errors.New("cannot infer field from expression")
 	}
-	return dag.Assignment{Kind: "Assignment", LHS: lhs, RHS: rhs}, nil
+	return path, nil
 }
 
 func (a *analyzer) semFields(exprs []ast.Expr) ([]dag.Expr, error) {