filters: put libexec/filters dirs before default PATH

Some distro packages install binaries in /usr/bin that clash with some
of aerc's builtin filters (for example, colorize and wrap). The issue is
that aerc filters dir (usually /usr/libexec/aerc/filters) is *after*
/usr/bin, making the builtin filters not accessible when these distro
packages are installed.

Since this mostly concerns colorize and wrap, move $LIBEXEC/aerc/filters
at the beginning of the exec PATH when running filter commands. If the
intent is **really** to execute /usr/bin/colorize or /usr/bin/html, then
their absolute paths should be used.

Link: https://archlinux.org/packages/extra/x86_64/talkfilters/
Link: https://tracker.debian.org/pkg/colorize
Signed-off-by: Robin Jarry <robin@jarry.cc>
Reviewed-by: Tristan Partin <tristan@partin.io>

4 files changed, 16 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0af1cb45..3c7c3764 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Names formatted like "Last Name, First Name" are better supported in templates
 - Composing an email is now aborted if the text editor exits with an error
   (e.g. with `vim`, abort an email with `:cq`).
+- Aerc builtin filters path (usually `/usr/libexec/aerc/filters`) is now
+  **prepended** to the default system `PATH` to avoid conflicts with installed
+  distro binaries which have the same name as aerc builtin filters (e.g.
+  `/usr/bin/colorize`).
 
 ## [0.15.2](https://git.sr.ht/~rjarry/aerc/refs/0.15.2) - 2023-05-11
 
diff --git a/config/aerc.conf b/config/aerc.conf
index 79a3936a..3eb30c45 100644
--- a/config/aerc.conf
+++ b/config/aerc.conf
@@ -469,7 +469,7 @@
 # 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 commands are invoked with sh -c. The following folders are prepended to
 # the system $PATH to allow referencing filters from their name only:
 #
 #   ${XDG_CONFIG_HOME:-~/.config}/aerc/filters
@@ -480,6 +480,9 @@
 #   /usr/libexec/aerc/filters
 #   /usr/share/aerc/filters
 #
+# If you want to run a program in your default $PATH which has the same name
+# as a builtin filter (e.g. /usr/bin/colorize), use its absolute path.
+#
 # The following variables are defined in the filter command environment:
 #
 #   AERC_MIME_TYPE      the part MIME type/subtype
diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index 0cdad99b..e420d52c 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -664,7 +664,7 @@ _/usr/libexec/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 *$PATH* to allow referencing filters from their name only.
+prepended to the system *$PATH* to allow referencing filters from their name only.
 
 ```
 ${XDG_CONFIG_HOME:-~/.config}/aerc/filters
@@ -676,6 +676,9 @@ $PREFIX/share/aerc/filters
 /usr/share/aerc/filters
 ```
 
+If you want to run a program in your default *$PATH* which has the same
+name as a builtin filter (e.g. _/usr/bin/colorize_), use its absolute path.
+
 The following variables are defined in the filter command environment:
 
 *AERC_MIME_TYPE*
diff --git a/widgets/msgviewer.go b/widgets/msgviewer.go
index 987d3133..d1bee8c6 100644
--- a/widgets/msgviewer.go
+++ b/widgets/msgviewer.go
@@ -598,9 +598,12 @@ func NewPartViewer(
 	var noFilter *ui.Grid
 	if filter != nil {
 		path, _ := os.LookupEnv("PATH")
+		var paths []string
 		for _, dir := range config.SearchDirs {
-			path += fmt.Sprintf(":%s/filters", dir)
+			paths = append(paths, dir+"/filters")
 		}
+		paths = append(paths, path)
+		path = strings.Join(paths, ":")
 		filter.Env = os.Environ()
 		filter.Env = append(filter.Env, fmt.Sprintf("PATH=%s", path))
 		filter.Env = append(filter.Env,