fix(flake): Nix builds release + always specifies target triple

Patch is necessary because Nix doesn't believe in testing what's not
being distributed (the release version).
See (unofficial) https://ryantm.github.io/nixpkgs/languages-frameworks/rust/#tests-relying-on-the-structure-of-the-target-directory.

And since Nix supports distributing to multiple architectures, target
architecture is always specified.

Author: x10an14

flake.nix

@@ -25,6 +25,80 @@
         pkgs = import inputs.nixpkgs {
           inherit system overlays;
         };
+        integrationTestPatch = pkgs.writeTextFile {
+          name = "integration-tests-nix-fix.patch";
+          text =
+            # patch
+            ''
+              diff --git a/tests/main.rs b/tests/main.rs
+              index c19811d..33c3829 100644
+              --- a/tests/main.rs
+              +++ b/tests/main.rs
+              @@ -15,7 +15,7 @@ fn failure_with_invalid_config() {
+                   let config_file = dir.path().join("nufmt.nuon");
+                   fs::write(&config_file, r#"{unknown: 1}"#).unwrap();
+
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--config")
+                       .arg(config_file.to_str().unwrap())
+                       .arg(dir.path().to_str().unwrap())
+              @@ -29,7 +29,7 @@ fn failure_with_invalid_config() {
+
+               #[test]
+               fn failure_with_invalid_config_file() {
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--config")
+                       .arg("path/that/does/not/exist/nufmt.nuon")
+                       .output()
+              @@ -42,7 +42,7 @@ fn failure_with_invalid_config_file() {
+
+               #[test]
+               fn failure_with_invalid_file_to_format() {
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("path/that/does/not/exist/a.nu")
+                       .output()
+                       .unwrap();
+              @@ -56,7 +56,7 @@ fn failure_with_invalid_file_to_format() {
+               fn warning_when_no_files_are_detected() {
+                   let dir = tempdir().unwrap();
+
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--dry-run")
+                       .arg(dir.path().to_str().unwrap())
+                       .output()
+              @@ -75,7 +75,7 @@ fn warning_is_displayed_when_no_files_are_detected_with_excluded_files() {
+                   fs::write(&config_file, r#"{exclude: ["a*"]}"#).unwrap();
+                   fs::write(&file_a, INVALID).unwrap();
+
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--config")
+                       .arg(config_file.to_str().unwrap())
+                       .arg("--dry-run")
+              @@ -98,7 +98,7 @@ fn files_are_reformatted() {
+                   fs::write(&file_a, INVALID).unwrap();
+                   fs::write(&file_b, INVALID).unwrap();
+
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--config")
+                       .arg(config_file.to_str().unwrap())
+                       .arg(dir.path().to_str().unwrap())
+              @@ -122,7 +122,7 @@ fn files_are_checked() {
+                   fs::write(&file_a, INVALID).unwrap();
+                   fs::write(&file_b, INVALID).unwrap();
+
+              -    let output = Command::new("target/debug/nufmt")
+              +    let output = Command::new("target/@target_triple@/release/nufmt")
+                       .arg("--config")
+                       .arg(config_file.to_str().unwrap())
+                       .arg("--dry-run")
+            '';
+        };
       in
       {
         devShells.default = pkgs.mkShell {
@@ -41,6 +115,11 @@
         packages.nufmt = pkgs.rustPlatform.buildRustPackage {
           name = "nufmt";
           src = ./.;
+          patches = [
+            (pkgs.replaceVars "${integrationTestPatch}" {
+              target_triple = pkgs.stdenv.hostPlatform.rust.rustcTarget;
+            })
+          ];
           cargoLock.lockFile = ./Cargo.lock;
         };