block compilation if both backends are enabled

CHANGELOG.md

@@ -9,6 +9,8 @@ Dates are given in YYYY-MM-DD format.
 - Nicer version output: `fif -V` reports "fif v0.3.2" (instead of just "fif 0.3.2" without the "v"), and `fif --version`
   reports `fif v0.3.2 (XDG-Mime backend)`, or whatever backend you're using
 - fif's trace output now includes its version, backend, operating system, and architecture
+- Block compilation if both the `xdg-mime-backend` and `infer-backend`
+  [features](https://gitlab.com/Lynnesbian/fif/-/wikis/Cargo-Features) are enabled
 
 ### v0.3.1 (2021-07-06)
 #### Features
@@ -151,7 +153,7 @@ Dates are given in YYYY-MM-DD format.
 #### Features
 - Added extension sets -- you can now use, for example, `-E images` to check files with known image extensions
 - Shell script output now uses `printf` instead of `echo`
-- Added [`infer`] backend
+- Added [`infer`] backend, configurable with [Cargo features](https://gitlab.com/Lynnesbian/fif/-/wikis/Cargo-Features)
 #### Bugfixes
 - Fixed broken singlethreaded support
 #### Other

build.rs

@@ -0,0 +1,10 @@
+#[allow(unreachable_code, clippy::pedantic)]
+fn main() -> Result<(), String> {
+	#[cfg(all(feature = "infer-backend", feature = "xdg-mime-backend"))]
+	// fail build if the user has set both the infer and xdg-mime backends
+	return Err(String::from(
+		"fif cannot be compiled with multiple backends set - please enable only one, or use the default.",
+	));
+
+	Ok(())
+}

src/main.rs

@@ -34,8 +34,8 @@ use crate::findings::ScanError;
 use crate::formats::{Format, PowerShell, Shell};
 use crate::mime_db::MimeDb;
 use crate::parameters::{OutputFormat, ScanOpts};
-use std::collections::BTreeSet;
 use crate::utils::{clap_long_version, os_name};
+use std::collections::BTreeSet;
 
 mod findings;
 mod formats;
@@ -72,7 +72,12 @@ fn main() {
 		// .target(env_logger::Target::Stdout) // log to stdout rather than stderr
 		.init();
 
-	trace!("fif {}, running on {} {}", clap_long_version(), std::env::consts::ARCH, os_name());
+	trace!(
+		"fif {}, running on {} {}",
+		clap_long_version(),
+		std::env::consts::ARCH,
+		os_name()
+	);
 	trace!("Initialise mimetype database");
 	init_db();