Avoid loading fieldnorms when not necessary

src/query/term_query/term_query.rs

@@ -93,6 +93,13 @@ impl TermQuery {
         scoring_enabled: bool,
     ) -> crate::Result<TermWeight> {
         let term = self.term.clone();
+        let field_entry = searcher.schema().get_field_entry(term.field());
+        if !field_entry.is_indexed() {
+            return Err(crate::TantivyError::SchemaError(format!(
+                "Field {:?} is not indexed",
+                field_entry.name()
+            )));
+        }
         let bm25_weight = BM25Weight::for_terms(searcher, &[term])?;
         let index_record_option = if scoring_enabled {
             self.index_record_option
@@ -103,6 +110,7 @@ impl TermQuery {
             self.term.clone(),
             index_record_option,
             bm25_weight,
+            scoring_enabled,
         ))
     }
 }

src/query/term_query/term_weight.rs

@@ -1,6 +1,7 @@
 use super::term_scorer::TermScorer;
 use crate::core::SegmentReader;
 use crate::docset::DocSet;
+use crate::fieldnorm::FieldNormReader;
 use crate::postings::SegmentPostings;
 use crate::query::bm25::BM25Weight;
 use crate::query::explanation::does_not_match;
@@ -15,6 +16,7 @@ pub struct TermWeight {
     term: Term,
     index_record_option: IndexRecordOption,
     similarity_weight: BM25Weight,
+    scoring_enabled: bool,
 }
 
 impl Weight for TermWeight {
@@ -87,11 +89,13 @@ impl TermWeight {
         term: Term,
         index_record_option: IndexRecordOption,
         similarity_weight: BM25Weight,
+        scoring_enabled: bool,
     ) -> TermWeight {
         TermWeight {
             term,
             index_record_option,
             similarity_weight,
+            scoring_enabled,
         }
     }
 
@@ -102,7 +106,11 @@ impl TermWeight {
     ) -> crate::Result<TermScorer> {
         let field = self.term.field();
         let inverted_index = reader.inverted_index(field)?;
-        let fieldnorm_reader = reader.get_fieldnorms_reader(field)?;
+        let fieldnorm_reader = if self.scoring_enabled {
+            reader.get_fieldnorms_reader(field)?
+        } else {
+            FieldNormReader::constant(reader.max_doc(), 1)
+        };
         let similarity_weight = self.similarity_weight.boost_by(boost);
         let postings_opt: Option<SegmentPostings> =
             inverted_index.read_postings(&self.term, self.index_record_option)?;