fix(code search): use alphanumeric tokenizer instead of letter tokenizer

letter tokenizer fails to consider numbers, this results in a searches for "func1" to match "func2" even with exact search.

furthermore, since the tokenizer did not consider numbers searches for numerical values such "2.42" would fail entirely

modules/indexer/code/bleve/bleve.go

@@ -17,6 +17,7 @@ import (
 	"code.gitea.io/gitea/modules/charset"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/gitrepo"
+	alphanum_tokenizer "code.gitea.io/gitea/modules/indexer/code/bleve/tokenizer/alphanum"
 	"code.gitea.io/gitea/modules/indexer/code/internal"
 	indexer_internal "code.gitea.io/gitea/modules/indexer/internal"
 	inner_bleve "code.gitea.io/gitea/modules/indexer/internal/bleve"
@@ -30,7 +31,6 @@ import (
 	"github.com/blevesearch/bleve/v2/analysis/token/camelcase"
 	"github.com/blevesearch/bleve/v2/analysis/token/lowercase"
 	"github.com/blevesearch/bleve/v2/analysis/token/unicodenorm"
-	"github.com/blevesearch/bleve/v2/analysis/tokenizer/letter"
 	"github.com/blevesearch/bleve/v2/mapping"
 	"github.com/blevesearch/bleve/v2/search/query"
 	"github.com/go-enry/go-enry/v2"
@@ -95,7 +95,7 @@ func generateBleveIndexMapping() (mapping.IndexMapping, error) {
 	} else if err := mapping.AddCustomAnalyzer(repoIndexerAnalyzer, map[string]any{
 		"type":          analyzer_custom.Name,
 		"char_filters":  []string{},
-		"tokenizer":     letter.Name,
+		"tokenizer":     alphanum_tokenizer.Name,
 		"token_filters": []string{unicodeNormalizeName, camelcase.Name, lowercase.Name},
 	}); err != nil {
 		return nil, err

modules/indexer/code/bleve/tokenizer/alphanum/alphanum.go

@@ -0,0 +1,23 @@
+package alphanum
+
+import (
+	"unicode"
+
+	"github.com/blevesearch/bleve/v2/analysis"
+	"github.com/blevesearch/bleve/v2/analysis/tokenizer/character"
+	"github.com/blevesearch/bleve/v2/registry"
+)
+
+const Name = "alphanum"
+
+func alphaNumeric(r rune) bool {
+	return unicode.IsLetter(r) || unicode.IsNumber(r)
+}
+
+func TokenizerConstructor(config map[string]any, cache *registry.Cache) (analysis.Tokenizer, error) {
+	return character.NewCharacterTokenizer(IsAlphaNumeric), nil
+}
+
+func init() {
+	registry.RegisterTokenizer(Name, TokenizerConstructor)
+}

modules/indexer/code/elasticsearch/elasticsearch.go

@@ -63,13 +63,13 @@ const (
 					"content_analyzer": {
 						"tokenizer": "content_tokenizer",
 						"filter" : ["lowercase"]
-					},
+					}
       			},
 				"tokenizer": {
 					"content_tokenizer": {
 						"type": "simple_pattern_split",
 						"pattern": "[^a-zA-Z0-9]"
-					},
+					}
 				}
 			}
 		},

modules/indexer/internal/bleve/util.go

@@ -80,10 +80,10 @@ func guessFuzzinessByKeyword(s string) int {
 	// according to https://github.com/blevesearch/bleve/issues/1563, the supported max fuzziness is 2
 	// magic number 4 was chosen to determine the levenshtein distance per each character of a keyword
 	// BUT, when using CJK (eg: `갃갃갃` `啊啊啊`), it mismatches a lot.
-	// Likewise, queries whose terms contains characters that are *not* letters should not use fuzziness
+	// Likewise, queries whose terms contains characters that are *not* letters or digits should not use fuzziness
 
 	for _, r := range s {
-		if r >= 128 || !unicode.IsLetter(r) {
+		if r >= 128 || !(unicode.IsLetter(r) || unicode.IsNumber(r)) {
 			return 0
 		}
 	}

modules/indexer/internal/bleve/util_test.go

@@ -37,6 +37,10 @@ func TestBleveGuessFuzzinessByKeyword(t *testing.T) {
 		},
 		{
 			Input:     "repo1",
+			Fuzziness: 1,
+		},
+		{
+			Input:     "repo_one",
 			Fuzziness: 0,
 		},
 		{