compiler/semantic: refactor sem.FileScan.Type initialization (#6291)

Initializing this field in translator.fileScanColumns doesn't make much
sense.  Remove that method and initialize the field in
translator.semFile along with the rest of sem.FileScan.

Author: nwt

compiler/semantic/op.go

@@ -1,7 +1,6 @@
 package semantic
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"net/url"
@@ -101,8 +100,12 @@ func (t *translator) semFromEntity(entity ast.FromEntity, alias *ast.TableAlias,
 		}
 		op, def := t.semFromName(entity, entity.Text, args)
 		if op, ok := op.(*sem.FileScan); ok {
-			if cols, ok := t.fileScanColumns(op); ok {
-				schema := schema(&staticSchema{def, cols})
+			if rec := super.TypeRecordOf(op.Type); rec != nil {
+				var columns []string
+				for _, f := range rec.Fields {
+					columns = append(columns, f.Name)
+				}
+				schema := schema(&staticSchema{def, columns})
 				seq, schema, err := derefSchemaWithAlias(op, schema, alias, sem.Seq{op})
 				if err != nil {
 					t.error(alias, err)
@@ -145,33 +148,6 @@ func (t *translator) fromCTE(entity ast.FromEntity, c *ast.SQLCTE, alias *ast.Ta
 	return seq, schema
 }
 
-// XXX this should find a type from the schema rather than the columns
-func (t *translator) fileScanColumns(op *sem.FileScan) ([]string, bool) {
-	if op.Format != "parquet" {
-		return nil, false
-	}
-	uri, err := storage.ParseURI(op.Path)
-	if err != nil {
-		return nil, false
-	}
-	ctx, cancel := context.WithCancel(t.ctx)
-	defer cancel()
-	sr, err := t.env.Engine().Get(ctx, uri)
-	if err != nil {
-		return nil, false
-	}
-	defer sr.Close()
-	op.Type = parquetio.Type(t.sctx, sr)
-	if op.Type == nil {
-		return nil, false
-	}
-	var cols []string
-	for _, f := range op.Type.(*super.TypeRecord).Fields {
-		cols = append(cols, f.Name)
-	}
-	return cols, true
-}
-
 func (t *translator) semFromExpr(entity *ast.ExprEntity, args []ast.OpArg, seq sem.Seq) (sem.Seq, string) {
 	expr := t.semExpr(entity.Expr)
 	val, ok := t.maybeEval(expr)
@@ -260,13 +236,34 @@ func (t *translator) semFile(n ast.Node, name string, args []ast.OpArg) sem.Op {
 	if format == "" {
 		format = sio.FormatFromPath(name)
 	}
+	typ, err := t.fileType(name, format)
+	if err != nil {
+		t.error(n, err)
+	}
 	return &sem.FileScan{
 		Node:   n,
+		Type:   typ,
 		Path:   name,
 		Format: format,
 	}
 }
 
+func (t *translator) fileType(path, format string) (super.Type, error) {
+	if format != "parquet" {
+		return nil, nil
+	}
+	uri, err := storage.ParseURI(path)
+	if err != nil {
+		return nil, err
+	}
+	r, err := t.env.Engine().Get(t.ctx, uri)
+	if err != nil {
+		return nil, err
+	}
+	defer r.Close()
+	return parquetio.Type(t.sctx, r), nil
+}
+
 func (t *translator) semFromFileGlob(globLoc ast.Node, pattern string, args []ast.OpArg) sem.Op {
 	names, err := filepath.Glob(pattern)
 	if err != nil {