1 files changed, 286 insertions, 0 deletions
diff --git a/modules/git/repo_attribute.go b/modules/git/repo_attribute.go
new file mode 100644
index 0000000..3ccc1b8
--- /dev/null
+++ b/modules/git/repo_attribute.go
@@ -0,0 +1,286 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"sync/atomic"
+
+	"code.gitea.io/gitea/modules/optional"
+)
+
+var LinguistAttributes = []string{"linguist-vendored", "linguist-generated", "linguist-language", "gitlab-language", "linguist-documentation", "linguist-detectable"}
+
+// newCheckAttrStdoutReader parses the nul-byte separated output of git check-attr on each call of
+// the returned function. The first reading error will stop the reading and be returned on all
+// subsequent calls.
+func newCheckAttrStdoutReader(r io.Reader, count int) func() (map[string]GitAttribute, error) {
+	scanner := bufio.NewScanner(r)
+
+	// adapted from bufio.ScanLines to split on nul-byte \x00
+	scanner.Split(func(data []byte, atEOF bool) (advance int, token []byte, err error) {
+		if atEOF && len(data) == 0 {
+			return 0, nil, nil
+		}
+		if i := bytes.IndexByte(data, '\x00'); i >= 0 {
+			// We have a full nul-terminated line.
+			return i + 1, data[0:i], nil
+		}
+		// If we're at EOF, we have a final, non-terminated line. Return it.
+		if atEOF {
+			return len(data), data, nil
+		}
+		// Request more data.
+		return 0, nil, nil
+	})
+
+	var err error
+	nextText := func() string {
+		if err != nil {
+			return ""
+		}
+		if !scanner.Scan() {
+			err = scanner.Err()
+			if err == nil {
+				err = io.ErrUnexpectedEOF
+			}
+			return ""
+		}
+		return scanner.Text()
+	}
+	nextAttribute := func() (string, GitAttribute, error) {
+		nextText() // discard filename
+		key := nextText()
+		value := GitAttribute(nextText())
+		return key, value, err
+	}
+	return func() (map[string]GitAttribute, error) {
+		values := make(map[string]GitAttribute, count)
+		for range count {
+			k, v, err := nextAttribute()
+			if err != nil {
+				return values, err
+			}
+			values[k] = v
+		}
+		return values, scanner.Err()
+	}
+}
+
+// GitAttribute exposes an attribute from the .gitattribute file
+type GitAttribute string //nolint:revive
+
+// IsSpecified returns true if the gitattribute is set and not empty
+func (ca GitAttribute) IsSpecified() bool {
+	return ca != "" && ca != "unspecified"
+}
+
+// String returns the value of the attribute or "" if unspecified
+func (ca GitAttribute) String() string {
+	if !ca.IsSpecified() {
+		return ""
+	}
+	return string(ca)
+}
+
+// Prefix returns the value of the attribute before any question mark '?'
+//
+// sometimes used within gitlab-language: https://docs.gitlab.com/ee/user/project/highlighting.html#override-syntax-highlighting-for-a-file-type
+func (ca GitAttribute) Prefix() string {
+	s := ca.String()
+	if i := strings.IndexByte(s, '?'); i >= 0 {
+		return s[:i]
+	}
+	return s
+}
+
+// Bool returns true if "set"/"true", false if "unset"/"false", none otherwise
+func (ca GitAttribute) Bool() optional.Option[bool] {
+	switch ca {
+	case "set", "true":
+		return optional.Some(true)
+	case "unset", "false":
+		return optional.Some(false)
+	}
+	return optional.None[bool]()
+}
+
+// gitCheckAttrCommand prepares the "git check-attr" command for later use as one-shot or streaming
+// instantiation.
+func (repo *Repository) gitCheckAttrCommand(treeish string, attributes ...string) (*Command, *RunOpts, context.CancelFunc, error) {
+	if len(attributes) == 0 {
+		return nil, nil, nil, fmt.Errorf("no provided attributes to check-attr")
+	}
+
+	env := os.Environ()
+	var removeTempFiles context.CancelFunc = func() {}
+
+	// git < 2.40 cannot run check-attr on bare repo, but needs INDEX + WORK_TREE
+	hasIndex := treeish == ""
+	if !hasIndex && !SupportCheckAttrOnBare {
+		indexFilename, worktree, cancel, err := repo.ReadTreeToTemporaryIndex(treeish)
+		if err != nil {
+			return nil, nil, nil, err
+		}
+		removeTempFiles = cancel
+
+		env = append(env, "GIT_INDEX_FILE="+indexFilename, "GIT_WORK_TREE="+worktree)
+
+		hasIndex = true
+
+		// clear treeish to read from provided index/work_tree
+		treeish = ""
+	}
+
+	cmd := NewCommand(repo.Ctx, "check-attr", "-z")
+
+	if hasIndex {
+		cmd.AddArguments("--cached")
+	}
+
+	if len(treeish) > 0 {
+		cmd.AddArguments("--source")
+		cmd.AddDynamicArguments(treeish)
+	}
+	cmd.AddDynamicArguments(attributes...)
+
+	// Version 2.43.1 has a bug where the behavior of `GIT_FLUSH` is flipped.
+	// Ref: https://lore.kernel.org/git/CABn0oJvg3M_kBW-u=j3QhKnO=6QOzk-YFTgonYw_UvFS1NTX4g@mail.gmail.com
+	if InvertedGitFlushEnv {
+		env = append(env, "GIT_FLUSH=0")
+	} else {
+		env = append(env, "GIT_FLUSH=1")
+	}
+
+	return cmd, &RunOpts{
+		Env: env,
+		Dir: repo.Path,
+	}, removeTempFiles, nil
+}
+
+// GitAttributeFirst returns the first specified attribute of the given filename.
+//
+// If treeish is empty, the gitattribute will be read from the current repo (which MUST be a working directory and NOT bare).
+func (repo *Repository) GitAttributeFirst(treeish, filename string, attributes ...string) (GitAttribute, error) {
+	values, err := repo.GitAttributes(treeish, filename, attributes...)
+	if err != nil {
+		return "", err
+	}
+	for _, a := range attributes {
+		if values[a].IsSpecified() {
+			return values[a], nil
+		}
+	}
+	return "", nil
+}
+
+// GitAttributes returns the gitattribute of the given filename.
+//
+// If treeish is empty, the gitattribute will be read from the current repo (which MUST be a working directory and NOT bare).
+func (repo *Repository) GitAttributes(treeish, filename string, attributes ...string) (map[string]GitAttribute, error) {
+	cmd, runOpts, removeTempFiles, err := repo.gitCheckAttrCommand(treeish, attributes...)
+	if err != nil {
+		return nil, err
+	}
+	defer removeTempFiles()
+
+	stdOut := new(bytes.Buffer)
+	runOpts.Stdout = stdOut
+
+	stdErr := new(bytes.Buffer)
+	runOpts.Stderr = stdErr
+
+	cmd.AddDashesAndList(filename)
+
+	if err := cmd.Run(runOpts); err != nil {
+		return nil, fmt.Errorf("failed to run check-attr: %w\n%s\n%s", err, stdOut.String(), stdErr.String())
+	}
+
+	return newCheckAttrStdoutReader(stdOut, len(attributes))()
+}
+
+// GitAttributeChecker creates an AttributeChecker for the given repository and provided commit ID
+// to retrieve the attributes of multiple files. The AttributeChecker must be closed after use.
+//
+// If treeish is empty, the gitattribute will be read from the current repo (which MUST be a working directory and NOT bare).
+func (repo *Repository) GitAttributeChecker(treeish string, attributes ...string) (AttributeChecker, error) {
+	cmd, runOpts, removeTempFiles, err := repo.gitCheckAttrCommand(treeish, attributes...)
+	if err != nil {
+		return AttributeChecker{}, err
+	}
+
+	cmd.AddArguments("--stdin")
+
+	// os.Pipe is needed (and not io.Pipe), otherwise cmd.Wait will wait for the stdinReader
+	// to be closed before returning (which would require another goroutine)
+	// https://go.dev/issue/23019
+	stdinReader, stdinWriter, err := os.Pipe() // reader closed in goroutine / writer closed on ac.Close
+	if err != nil {
+		return AttributeChecker{}, err
+	}
+	stdoutReader, stdoutWriter := io.Pipe() // closed in goroutine
+
+	ac := AttributeChecker{
+		removeTempFiles: removeTempFiles, // called on ac.Close
+		stdinWriter:     stdinWriter,
+		readStdout:      newCheckAttrStdoutReader(stdoutReader, len(attributes)),
+		err:             &atomic.Value{},
+	}
+
+	go func() {
+		defer stdinReader.Close()
+		defer stdoutWriter.Close() // in case of a panic (no-op if already closed by CloseWithError at the end)
+
+		stdErr := new(bytes.Buffer)
+		runOpts.Stdin = stdinReader
+		runOpts.Stdout = stdoutWriter
+		runOpts.Stderr = stdErr
+
+		err := cmd.Run(runOpts)
+
+		// if the context was cancelled, Run error is irrelevant
+		if e := cmd.parentContext.Err(); e != nil {
+			err = e
+		}
+
+		if err != nil { // decorate the returned error
+			err = fmt.Errorf("git check-attr (stderr: %q): %w", strings.TrimSpace(stdErr.String()), err)
+			ac.err.Store(err)
+		}
+		stdoutWriter.CloseWithError(err)
+	}()
+
+	return ac, nil
+}
+
+type AttributeChecker struct {
+	removeTempFiles context.CancelFunc
+	stdinWriter     io.WriteCloser
+	readStdout      func() (map[string]GitAttribute, error)
+	err             *atomic.Value
+}
+
+func (ac AttributeChecker) CheckPath(path string) (map[string]GitAttribute, error) {
+	if _, err := ac.stdinWriter.Write([]byte(path + "\x00")); err != nil {
+		// try to return the Run error if available, since it is likely more helpful
+		// than just "broken pipe"
+		if aerr, _ := ac.err.Load().(error); aerr != nil {
+			return nil, aerr
+		}
+		return nil, fmt.Errorf("git check-attr: %w", err)
+	}
+
+	return ac.readStdout()
+}
+
+func (ac AttributeChecker) Close() error {
+	ac.removeTempFiles()
+	return ac.stdinWriter.Close()
+}