filters: append well known dirs to exec PATH

To allow referencing built-in filters without hard coding a path during
installation, append the following folders to the exec PATH when running
the filter commands:

	~/.config/aerc/filters
	~/.local/share/aerc/filters
	$PREFIX/share/aerc/filters
	/usr/share/aerc/filters

If a filter script has the same name than a command in the default exec
PATH, it will not shadow it. In that edge case, the absolute path to the
filter script must be specified.

Suggested-by: Teo Luppi <me@luppi.uk>
Signed-off-by: Robin Jarry <robin@jarry.cc>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>

CHANGELOG.md

@@ -28,6 +28,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   history.
 - Embedded terminal backend (libvterm was replaced by a pure go implementation).
 - Use event driven loop instead of Tick based
+- Filter commands are now executed with
+  `:~/.config/aerc/filters:~/.local/share/aerc/filters:$PREFIX/share/aerc/filters:/usr/share/aerc/filters`
+  appended to the exec `PATH`. This allows referencing aerc's built-in filter
+  scripts from their name only.
 
 ### Fixed
 

config/aerc.conf

@@ -302,6 +302,14 @@ reply-to-self=true
 # Filters allow you to pipe an email body through a shell command to render
 # certain emails differently, e.g. highlighting them with ANSI escape codes.
 #
+# The commands are invoked with sh -c. The following folders are appended to
+# the system $PATH to allow referencing filters from their name only:
+#
+#   ${XDG_CONFIG_HOME:-~/.config}/aerc/filters
+#   ${XDG_DATA_HOME:-~/.local/share}/aerc/filters
+#   $PREFIX/share/aerc/filters
+#   /usr/share/aerc/filters
+#
 # The first filter which matches the email's mimetype will be used, so order
 # them from most to least specific.
 #

config/config.go

@@ -426,7 +426,7 @@ func buildDefaultDirs() []string {
 	return defaultDirs
 }
 
-var searchDirs = buildDefaultDirs()
+var SearchDirs = buildDefaultDirs()
 
 func installTemplate(root, name string) error {
 	var err error
@@ -437,7 +437,7 @@ func installTemplate(root, name string) error {
 		}
 	}
 	var data []byte
-	for _, dir := range searchDirs {
+	for _, dir := range SearchDirs {
 		data, err = os.ReadFile(path.Join(dir, name))
 		if err == nil {
 			break
@@ -597,7 +597,7 @@ func (config *AercConfig) LoadConfig(file *ini.File) error {
 	}
 
 	// append default paths to template-dirs and styleset-dirs
-	for _, dir := range searchDirs {
+	for _, dir := range SearchDirs {
 		config.Ui.StyleSetDirs = append(
 			config.Ui.StyleSetDirs, path.Join(dir, "stylesets"),
 		)

doc/aerc-config.5.scd

@@ -510,6 +510,16 @@ aerc ships with some default filters installed in the share directory (usually
 _/usr/share/aerc/filters_). Note that these may have additional dependencies
 that aerc does not have alone.
 
+The filter commands are invoked with sh -c [command]. The following folders are
+appended to the system $PATH to allow referencing filters from their name only.
+
+```
+${XDG_CONFIG_HOME:-~/.config}/aerc/filters
+${XDG_DATA_HOME:-~/.local/share}/aerc/filters
+$PREFIX/share/aerc/filters
+/usr/share/aerc/filters
+```
+
 Note that said email body is converted into UTF-8 before being passed to
 filters.
 

widgets/msgviewer.go

@@ -577,6 +577,12 @@ func NewPartViewer(acct *AccountView, conf *config.AercConfig,
 		}
 	}
 	if filter != nil {
+		path, _ := os.LookupEnv("PATH")
+		for _, dir := range config.SearchDirs {
+			path += fmt.Sprintf(":%s/filters", dir)
+		}
+		filter.Env = os.Environ()
+		filter.Env = append(filter.Env, fmt.Sprintf("PATH=%s", path))
 		if pipe, err = filter.StdinPipe(); err != nil {
 			return nil, err
 		}