From e317f0d87949b044075884f8f7e3ef06d7badd4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micka=C3=ABl=20Menu?= <mickael.menu@gmail.com>
Date: Fri, 17 Dec 2021 13:07:21 +0100
Subject: [PATCH] Fix infinite loop when parsing a single-character hashtag
 (#119)

---
 CHANGELOG.md                                |  2 ++
 internal/adapter/markdown/extensions/tag.go |  6 +++++-
 internal/adapter/markdown/markdown_test.go  |  4 ++++
 main.go                                     | 20 ++++++++++++++++++++
 4 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e82679c..f101299 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,10 +9,12 @@ All notable changes to this project will be documented in this file.
 * New LSP commands:
     * [`zk.list`](docs/editors-integration.md#zklist) to search for notes.
     * [`zk.tag.list`](docs/editors-integration.md#zktaglist) to retrieve the list of tags.
+* `--debug` mode which prints a stacktrace on `SIGINT`.
 
 ### Fixed
 
 * [#111](https://github.com/mickael-menu/zk/issues/111) Filenames take precedence over folders when matching a sub-path with wiki links.
+* [#118](https://github.com/mickael-menu/zk/issues/118) Fix infinite loop when parsing a single-character hashtag.
 
 
 ## 0.8.0
diff --git a/internal/adapter/markdown/extensions/tag.go b/internal/adapter/markdown/extensions/tag.go
index d33ecb7..e2c2b6f 100644
--- a/internal/adapter/markdown/extensions/tag.go
+++ b/internal/adapter/markdown/extensions/tag.go
@@ -106,7 +106,11 @@ func (p *hashtagParser) Parse(parent ast.Node, block text.Reader, pc parser.Cont
 		}
 	}
 
-	for i, char := range string(line[1:]) {
+	for i, char := range string(line) {
+		if i == 0 {
+			// Skip the first character, as it is #
+			continue
+		}
 		if parsingMultiWordTag {
 			multiWordTagEndPos = i
 		} else {
diff --git a/internal/adapter/markdown/markdown_test.go b/internal/adapter/markdown/markdown_test.go
index 45d9df6..f12aa90 100644
--- a/internal/adapter/markdown/markdown_test.go
+++ b/internal/adapter/markdown/markdown_test.go
@@ -188,6 +188,10 @@ func TestParseHashtags(t *testing.T) {
 	test("##invalid also#invalid", []string{})
 	// Bear's multi multi-word tags are disabled
 	test("#multi word# end", []string{"multi"})
+
+	// Single character
+	// See https://github.com/mickael-menu/zk/issues/118
+	test("#a", []string{"a"})
 }
 
 func TestParseWordtags(t *testing.T) {
diff --git a/main.go b/main.go
index 029e17b..f2ad869 100644
--- a/main.go
+++ b/main.go
@@ -5,7 +5,9 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path/filepath"
+	"runtime"
 	"strings"
 
 	"github.com/alecthomas/kong"
@@ -31,6 +33,7 @@ var root struct {
 	NotebookDir string  `type:path placeholder:PATH help:"Turn off notebook auto-discovery and set manually the notebook where commands are run."`
 	WorkingDir  string  `short:W type:path placeholder:PATH help:"Run as if zk was started in <PATH> instead of the current working directory."`
 	NoInput     NoInput `help:"Never prompt or ask for confirmation."`
+	Debug       bool    `default:"0" help:"Print a debug stacktrace on SIGINT."`
 
 	ShowHelp ShowHelp         `cmd hidden default:"1"`
 	LSP      cmd.LSP          `cmd hidden`
@@ -84,6 +87,10 @@ func main() {
 		ctx, err := parser.Parse(args)
 		fatalIfError(err)
 
+		if root.Debug {
+			setupDebugMode()
+		}
+
 		// Index the current notebook except if the user is running the `index`
 		// command, otherwise it would hide the stats.
 		if ctx.Command() != "index" {
@@ -131,6 +138,19 @@ func fatalIfError(err error) {
 	}
 }
 
+func setupDebugMode() {
+	c := make(chan os.Signal)
+	go func() {
+		stacktrace := make([]byte, 8192)
+		for _ = range c {
+			length := runtime.Stack(stacktrace, true)
+			fmt.Fprintf(os.Stderr, "%s\n", string(stacktrace[:length]))
+			os.Exit(1)
+		}
+	}()
+	signal.Notify(c, os.Interrupt)
+}
+
 // runAlias will execute a user alias if the command is one of them.
 func runAlias(container *cli.Container, args []string) (bool, error) {
 	if len(args) < 1 {