[CHORE] Drop go-git support

See https://codeberg.org/forgejo/discussions/issues/164 for the
rationale and discussion of this change.

Everything related to the `go-git` dependency is dropped (Only a single
instance is left in a test file to test for an XSS, it requires crafting
an commit that Git itself refuses to craft). `_gogit` files have
been removed entirely, `go:build: !gogit` is removed, `XXX_nogogit.go` files
either have been renamed or had their code being merged into the
`XXX.go` file.

modules/git/parse.go

@@ -0,0 +1,137 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+// ParseTreeEntries parses the output of a `git ls-tree -l` command.
+func ParseTreeEntries(data []byte) ([]*TreeEntry, error) {
+	return parseTreeEntries(data, nil)
+}
+
+var sepSpace = []byte{' '}
+
+func parseTreeEntries(data []byte, ptree *Tree) ([]*TreeEntry, error) {
+	var err error
+	entries := make([]*TreeEntry, 0, bytes.Count(data, []byte{'\n'})+1)
+	for pos := 0; pos < len(data); {
+		// expect line to be of the form:
+		// <mode> <type> <sha> <space-padded-size>\t<filename>
+		// <mode> <type> <sha>\t<filename>
+		posEnd := bytes.IndexByte(data[pos:], '\n')
+		if posEnd == -1 {
+			posEnd = len(data)
+		} else {
+			posEnd += pos
+		}
+		line := data[pos:posEnd]
+		posTab := bytes.IndexByte(line, '\t')
+		if posTab == -1 {
+			return nil, fmt.Errorf("invalid ls-tree output (no tab): %q", line)
+		}
+
+		entry := new(TreeEntry)
+		entry.ptree = ptree
+
+		entryAttrs := line[:posTab]
+		entryName := line[posTab+1:]
+
+		entryMode, entryAttrs, _ := bytes.Cut(entryAttrs, sepSpace)
+		_ /* entryType */, entryAttrs, _ = bytes.Cut(entryAttrs, sepSpace) // the type is not used, the mode is enough to determine the type
+		entryObjectID, entryAttrs, _ := bytes.Cut(entryAttrs, sepSpace)
+		if len(entryAttrs) > 0 {
+			entrySize := entryAttrs // the last field is the space-padded-size
+			entry.size, _ = strconv.ParseInt(strings.TrimSpace(string(entrySize)), 10, 64)
+			entry.sized = true
+		}
+
+		switch string(entryMode) {
+		case "100644":
+			entry.entryMode = EntryModeBlob
+		case "100755":
+			entry.entryMode = EntryModeExec
+		case "120000":
+			entry.entryMode = EntryModeSymlink
+		case "160000":
+			entry.entryMode = EntryModeCommit
+		case "040000", "040755": // git uses 040000 for tree object, but some users may get 040755 for unknown reasons
+			entry.entryMode = EntryModeTree
+		default:
+			return nil, fmt.Errorf("unknown type: %v", string(entryMode))
+		}
+
+		entry.ID, err = NewIDFromString(string(entryObjectID))
+		if err != nil {
+			return nil, fmt.Errorf("invalid ls-tree output (invalid object id): %q, err: %w", line, err)
+		}
+
+		if len(entryName) > 0 && entryName[0] == '"' {
+			entry.name, err = strconv.Unquote(string(entryName))
+			if err != nil {
+				return nil, fmt.Errorf("invalid ls-tree output (invalid name): %q, err: %w", line, err)
+			}
+		} else {
+			entry.name = string(entryName)
+		}
+
+		pos = posEnd + 1
+		entries = append(entries, entry)
+	}
+	return entries, nil
+}
+
+func catBatchParseTreeEntries(objectFormat ObjectFormat, ptree *Tree, rd *bufio.Reader, sz int64) ([]*TreeEntry, error) {
+	fnameBuf := make([]byte, 4096)
+	modeBuf := make([]byte, 40)
+	shaBuf := make([]byte, objectFormat.FullLength())
+	entries := make([]*TreeEntry, 0, 10)
+
+loop:
+	for sz > 0 {
+		mode, fname, sha, count, err := ParseTreeLine(objectFormat, rd, modeBuf, fnameBuf, shaBuf)
+		if err != nil {
+			if err == io.EOF {
+				break loop
+			}
+			return nil, err
+		}
+		sz -= int64(count)
+		entry := new(TreeEntry)
+		entry.ptree = ptree
+
+		switch string(mode) {
+		case "100644":
+			entry.entryMode = EntryModeBlob
+		case "100755":
+			entry.entryMode = EntryModeExec
+		case "120000":
+			entry.entryMode = EntryModeSymlink
+		case "160000":
+			entry.entryMode = EntryModeCommit
+		case "40000", "40755": // git uses 40000 for tree object, but some users may get 40755 for unknown reasons
+			entry.entryMode = EntryModeTree
+		default:
+			log.Debug("Unknown mode: %v", string(mode))
+			return nil, fmt.Errorf("unknown mode: %v", string(mode))
+		}
+
+		entry.ID = objectFormat.MustID(sha)
+		entry.name = string(fname)
+		entries = append(entries, entry)
+	}
+	if _, err := rd.Discard(1); err != nil {
+		return entries, err
+	}
+
+	return entries, nil
+}