Refactor Git Attribute & performance optimization (#34154)

This PR moved git attributes related code to `modules/git/attribute` sub
package and moved language stats related code to
`modules/git/languagestats` sub package to make it easier to maintain.

And it also introduced a performance improvement which use the `git
check-attr --source` which can be run in a bare git repository so that
we don't need to create a git index file. The new parameter need a git
version >= 2.40 . If git version less than 2.40, it will fall back to
previous implementation.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>

modules/git/languagestats/language_stats_nogogit.go

@@ -0,0 +1,209 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !gogit
+
+package languagestats
+
+import (
+	"bytes"
+	"io"
+
+	"code.gitea.io/gitea/modules/analyze"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/git/attribute"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/optional"
+
+	"github.com/go-enry/go-enry/v2"
+)
+
+// GetLanguageStats calculates language stats for git repository at specified commit
+func GetLanguageStats(repo *git.Repository, commitID string) (map[string]int64, error) {
+	// We will feed the commit IDs in order into cat-file --batch, followed by blobs as necessary.
+	// so let's create a batch stdin and stdout
+	batchStdinWriter, batchReader, cancel, err := repo.CatFileBatch(repo.Ctx)
+	if err != nil {
+		return nil, err
+	}
+	defer cancel()
+
+	writeID := func(id string) error {
+		_, err := batchStdinWriter.Write([]byte(id + "\n"))
+		return err
+	}
+
+	if err := writeID(commitID); err != nil {
+		return nil, err
+	}
+	shaBytes, typ, size, err := git.ReadBatchLine(batchReader)
+	if typ != "commit" {
+		log.Debug("Unable to get commit for: %s. Err: %v", commitID, err)
+		return nil, git.ErrNotExist{ID: commitID}
+	}
+
+	sha, err := git.NewIDFromString(string(shaBytes))
+	if err != nil {
+		log.Debug("Unable to get commit for: %s. Err: %v", commitID, err)
+		return nil, git.ErrNotExist{ID: commitID}
+	}
+
+	commit, err := git.CommitFromReader(repo, sha, io.LimitReader(batchReader, size))
+	if err != nil {
+		log.Debug("Unable to get commit for: %s. Err: %v", commitID, err)
+		return nil, err
+	}
+	if _, err = batchReader.Discard(1); err != nil {
+		return nil, err
+	}
+
+	tree := commit.Tree
+
+	entries, err := tree.ListEntriesRecursiveWithSize()
+	if err != nil {
+		return nil, err
+	}
+
+	checker, err := attribute.NewBatchChecker(repo, commitID, attribute.LinguistAttributes)
+	if err != nil {
+		return nil, err
+	}
+	defer checker.Close()
+
+	contentBuf := bytes.Buffer{}
+	var content []byte
+
+	// sizes contains the current calculated size of all files by language
+	sizes := make(map[string]int64)
+	// by default we will only count the sizes of programming languages or markup languages
+	// unless they are explicitly set using linguist-language
+	includedLanguage := map[string]bool{}
+	// or if there's only one language in the repository
+	firstExcludedLanguage := ""
+	firstExcludedLanguageSize := int64(0)
+
+	for _, f := range entries {
+		select {
+		case <-repo.Ctx.Done():
+			return sizes, repo.Ctx.Err()
+		default:
+		}
+
+		contentBuf.Reset()
+		content = contentBuf.Bytes()
+
+		if f.Size() == 0 {
+			continue
+		}
+
+		isVendored := optional.None[bool]()
+		isGenerated := optional.None[bool]()
+		isDocumentation := optional.None[bool]()
+		isDetectable := optional.None[bool]()
+
+		attrs, err := checker.CheckPath(f.Name())
+		if err == nil {
+			if isVendored = attrs.GetVendored(); isVendored.ValueOrDefault(false) {
+				continue
+			}
+
+			if isGenerated = attrs.GetGenerated(); isGenerated.ValueOrDefault(false) {
+				continue
+			}
+
+			if isDocumentation = attrs.GetDocumentation(); isDocumentation.ValueOrDefault(false) {
+				continue
+			}
+
+			if isDetectable = attrs.GetDetectable(); !isDetectable.ValueOrDefault(true) {
+				continue
+			}
+
+			if hasLanguage := attrs.GetLanguage(); hasLanguage.Value() != "" {
+				language := hasLanguage.Value()
+
+				// group languages, such as Pug -> HTML; SCSS -> CSS
+				group := enry.GetLanguageGroup(language)
+				if len(group) != 0 {
+					language = group
+				}
+
+				// this language will always be added to the size
+				sizes[language] += f.Size()
+				continue
+			}
+		}
+
+		if (!isVendored.Has() && analyze.IsVendor(f.Name())) ||
+			enry.IsDotFile(f.Name()) ||
+			(!isDocumentation.Has() && enry.IsDocumentation(f.Name())) ||
+			enry.IsConfiguration(f.Name()) {
+			continue
+		}
+
+		// If content can not be read or file is too big just do detection by filename
+
+		if f.Size() <= bigFileSize {
+			if err := writeID(f.ID.String()); err != nil {
+				return nil, err
+			}
+			_, _, size, err := git.ReadBatchLine(batchReader)
+			if err != nil {
+				log.Debug("Error reading blob: %s Err: %v", f.ID.String(), err)
+				return nil, err
+			}
+
+			sizeToRead := size
+			discard := int64(1)
+			if size > fileSizeLimit {
+				sizeToRead = fileSizeLimit
+				discard = size - fileSizeLimit + 1
+			}
+
+			_, err = contentBuf.ReadFrom(io.LimitReader(batchReader, sizeToRead))
+			if err != nil {
+				return nil, err
+			}
+			content = contentBuf.Bytes()
+			if err := git.DiscardFull(batchReader, discard); err != nil {
+				return nil, err
+			}
+		}
+		if !isGenerated.Has() && enry.IsGenerated(f.Name(), content) {
+			continue
+		}
+
+		// FIXME: Why can't we split this and the IsGenerated tests to avoid reading the blob unless absolutely necessary?
+		// - eg. do the all the detection tests using filename first before reading content.
+		language := analyze.GetCodeLanguage(f.Name(), content)
+		if language == "" {
+			continue
+		}
+
+		// group languages, such as Pug -> HTML; SCSS -> CSS
+		group := enry.GetLanguageGroup(language)
+		if group != "" {
+			language = group
+		}
+
+		included, checked := includedLanguage[language]
+		if !checked {
+			langType := enry.GetLanguageType(language)
+			included = langType == enry.Programming || langType == enry.Markup
+			includedLanguage[language] = included
+		}
+		if included || isDetectable.ValueOrDefault(false) {
+			sizes[language] += f.Size()
+		} else if len(sizes) == 0 && (firstExcludedLanguage == "" || firstExcludedLanguage == language) {
+			firstExcludedLanguage = language
+			firstExcludedLanguageSize += f.Size()
+		}
+	}
+
+	// If there are no included languages add the first excluded language
+	if len(sizes) == 0 && firstExcludedLanguage != "" {
+		sizes[firstExcludedLanguage] = firstExcludedLanguageSize
+	}
+
+	return mergeLanguageStats(sizes), nil
+}