35 files changed, 665 insertions, 49 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 5b4b0eb..08881fd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -21,6 +21,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "arrayvec"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
+
+[[package]]
 name = "atty"
 version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -69,9 +75,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "clap"
-version = "3.0.0-beta.4"
+version = "3.0.0-beta.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fcd70aa5597dbc42f7217a543f9ef2768b2ef823ba29036072d30e1d88e98406"
+checksum = "feff3878564edb93745d58cf63e17b63f24142506e7a20c87a5521ed7bfb1d63"
 dependencies = [
  "atty",
  "bitflags",
@@ -82,14 +88,14 @@ dependencies = [
  "strsim",
  "termcolor",
  "textwrap",
- "vec_map",
+ "unicase",
 ]
 
 [[package]]
 name = "clap_derive"
-version = "3.0.0-beta.4"
+version = "3.0.0-beta.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b5bb0d655624a0b8770d1c178fb8ffcb1f91cc722cb08f451e3dc72465421ac"
+checksum = "8b15c6b4f786ffb6192ffe65a36855bc1fc2444bcd0945ae16748dcd6ed7d0d3"
 dependencies = [
  "heck",
  "proc-macro-error",
@@ -99,6 +105,19 @@ dependencies = [
 ]
 
 [[package]]
+name = "console"
+version = "0.14.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3993e6445baa160675931ec041a5e03ca84b9c6e32a056150d3aa2bdda0a1f45"
+dependencies = [
+ "encode_unicode",
+ "lazy_static",
+ "libc",
+ "terminal_size",
+ "winapi",
+]
+
+[[package]]
 name = "countme"
 version = "2.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -115,6 +134,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "dtoa"
+version = "0.4.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56899898ce76aaf4a0f24d914c97ea6ed976d42fec6ad33fcbb0a1103e07b2b0"
+
+[[package]]
+name = "encode_unicode"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a357d28ed41a50f9c765dbfe56cbc04a64e53e5fc58ba79fbc34c10ef3df831f"
+
+[[package]]
 name = "fnv"
 version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -198,6 +229,21 @@ dependencies = [
 ]
 
 [[package]]
+name = "insta"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15226a375927344c78d39dc6b49e2d5562a5b0705e26a589093c6792e52eed8e"
+dependencies = [
+ "console",
+ "lazy_static",
+ "serde",
+ "serde_json",
+ "serde_yaml",
+ "similar 1.3.0",
+ "uuid",
+]
+
+[[package]]
 name = "itoa"
 version = "0.4.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -224,9 +270,15 @@ dependencies = [
 
 [[package]]
 name = "libc"
-version = "0.2.103"
+version = "0.2.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dd8f7255a17a627354f321ef0055d63b898c6fb27eff628af4d1b66b7331edf6"
+checksum = "a60553f9a9e039a333b4e9b20573b9e9b9c0bb3a11e201ccc48ef4283456d673"
+
+[[package]]
+name = "linked-hash-map"
+version = "0.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7fb9b38af92608140b86b693604b9ffcc5824240a484d1ecd4795bacb2fe88f3"
 
 [[package]]
 name = "log"
@@ -278,9 +330,12 @@ checksum = "692fcb63b64b1758029e0a96ee63e049ce8c5948587f2f7208df04625e5f6b56"
 
 [[package]]
 name = "os_str_bytes"
-version = "3.1.0"
+version = "4.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6acbef58a60fe69ab50510a55bc8cdd4d6cf2283d27ad338f54cb52747a9cf2d"
+checksum = "addaa943333a514159c80c97ff4a93306530d965d27e139188283cd13e06a799"
+dependencies = [
+ "memchr",
+]
 
 [[package]]
 name = "proc-macro-error"
@@ -308,18 +363,18 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.29"
+version = "1.0.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b9f5105d4fdaab20335ca9565e106a5d9b82b6219b5ba735731124ac6711d23d"
+checksum = "ba508cc11742c0dc5c1659771673afbab7a0efab23aa17e854cbab0837ed0b43"
 dependencies = [
  "unicode-xid",
 ]
 
 [[package]]
 name = "quote"
-version = "1.0.9"
+version = "1.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3d0b9745dc2debf507c8422de05d7226cc1f0644216dfdfead988f9b1ab32a7"
+checksum = "38bc8cc6a5f2e3655e0899c1b848643b2562f853f114bfec7be120678e3ace05"
 dependencies = [
  "proc-macro2",
 ]
@@ -343,9 +398,9 @@ checksum = "f497285884f3fcff424ffc933e56d7cbca511def0c9831a7f9b5f6153e3cc89b"
 
 [[package]]
 name = "rnix"
-version = "0.9.0"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b37f8af07a0354606141df076458660af7e22238e4117a041c21c548080addd"
+checksum = "294becb48f58c496d96c10a12df290266204ca75c9799be4d04222bfaebb6a37"
 dependencies = [
  "cbitset",
  "rowan",
@@ -418,6 +473,24 @@ dependencies = [
 ]
 
 [[package]]
+name = "serde_yaml"
+version = "0.8.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8c608a35705a5d3cdc9fbe403147647ff34b921f8e833e49306df898f9b20af"
+dependencies = [
+ "dtoa",
+ "indexmap",
+ "serde",
+ "yaml-rust",
+]
+
+[[package]]
+name = "similar"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ad1d488a557b235fc46dae55512ffbfc429d2482b08b4d9435ab07384ca8aec"
+
+[[package]]
 name = "similar"
 version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -425,9 +498,12 @@ checksum = "2e24979f63a11545f5f2c60141afe249d4f19f84581ea2138065e400941d83d3"
 
 [[package]]
 name = "smol_str"
-version = "0.1.18"
+version = "0.1.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b203e79e90905594272c1c97c7af701533d42adaab0beb3859018e477d54a3b0"
+checksum = "559b173452ec4061933b0c0e22d7d429c90ecdc1b3ae1c6e64238e7c15c3ee15"
+dependencies = [
+ "serde",
+]
 
 [[package]]
 name = "statix"
@@ -436,16 +512,27 @@ dependencies = [
  "ariadne",
  "clap",
  "ignore",
+ "insta",
  "lib",
  "rnix",
  "serde",
  "serde_json",
- "similar",
+ "similar 2.1.0",
+ "strip-ansi-escapes",
  "thiserror",
  "vfs",
 ]
 
 [[package]]
+name = "strip-ansi-escapes"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "011cbb39cf7c1f62871aea3cc46e5817b0937b49e9447370c93cacbe93a766d8"
+dependencies = [
+ "vte",
+]
+
+[[package]]
 name = "strsim"
 version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -453,9 +540,9 @@ checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
 
 [[package]]
 name = "syn"
-version = "1.0.76"
+version = "1.0.81"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c6f107db402c2c2055242dbf4d2af0e69197202e9faacbef9571bbe47f5a1b84"
+checksum = "f2afee18b8beb5a596ecb4a2dce128c719b4ba399d34126b9e4396e3f9860966"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -472,6 +559,16 @@ dependencies = [
 ]
 
 [[package]]
+name = "terminal_size"
+version = "0.1.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "633c1a546cee861a1a6d0dc69ebeca693bf4296661ba7852b9d21d159e0506df"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
+[[package]]
 name = "text-size"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -516,6 +613,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "unicase"
+version = "2.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50f37be617794602aabbeee0be4f259dc1778fabe05e2d67ee8f79326d5cb4f6"
+dependencies = [
+ "version_check",
+]
+
+[[package]]
 name = "unicode-segmentation"
 version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -534,10 +640,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
 
 [[package]]
-name = "vec_map"
+name = "utf8parse"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "936e4b492acfd135421d8dca4b1aa80a7bfc26e702ef3af710e0752684df5372"
+
+[[package]]
+name = "uuid"
 version = "0.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f1bddf1187be692e79c5ffeab891132dfb0f236ed36a43c7ed39f1165ee20191"
+checksum = "bc5cf98d8186244414c848017f0e2676b3fcb46807f6668a97dfe67359a3c4b7"
 
 [[package]]
 name = "version_check"
@@ -553,6 +665,27 @@ dependencies = [
 ]
 
 [[package]]
+name = "vte"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6cbce692ab4ca2f1f3047fcf732430249c0e971bfdd2b234cf2c47ad93af5983"
+dependencies = [
+ "arrayvec",
+ "utf8parse",
+ "vte_generate_state_changes",
+]
+
+[[package]]
+name = "vte_generate_state_changes"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d257817081c7dffcdbab24b9e62d2def62e2ff7d00b1c20062551e6cccc145ff"
+dependencies = [
+ "proc-macro2",
+ "quote",
+]
+
+[[package]]
 name = "walkdir"
 version = "2.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -595,6 +728,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
 [[package]]
+name = "yaml-rust"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56c1936c4cc7a1c9ab21a1ebb602eb942ba868cbd44a99cb7cdc5892335e1c85"
+dependencies = [
+ "linked-hash-map",
+]
+
+[[package]]
 name = "yansi"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/bin/Cargo.toml b/bin/Cargo.toml
index d67e6c1..7c48083 100644
--- a/bin/Cargo.toml
+++ b/bin/Cargo.toml
@@ -6,7 +6,13 @@ license = "MIT"
 authors = [ "Akshay <[email protected]>" ]
 description = "Lints and suggestions for the Nix programming language"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[lib]
+name = "statix"
+path = "src/lib.rs"
+
+[[bin]]
+name = "statix"
+path = "src/main.rs"
 
 [dependencies]
 ariadne = "0.1.3"
@@ -27,5 +33,9 @@ version = "1.0.68"
 features = [ "derive" ]
 optional = true
 
+[dev-dependencies]
+insta = "1.8.0"
+strip-ansi-escapes = "0.1.1"
+
 [features]
 json = [ "lib/json-out", "serde_json", "serde" ]
diff --git a/bin/src/config.rs b/bin/src/config.rs
index 25c2a7f..d3944ac 100644
--- a/bin/src/config.rs
+++ b/bin/src/config.rs
@@ -2,17 +2,17 @@ use std::{default::Default, fmt, fs, path::PathBuf, str::FromStr};
 
 use crate::{dirs, err::ConfigErr};
 
-use clap::Clap;
+use clap::Parser;
 use vfs::ReadOnlyVfs;
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 #[clap(version, author, about)]
 pub struct Opts {
     #[clap(subcommand)]
     pub cmd: SubCommand,
 }
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 pub enum SubCommand {
     /// Lints and suggestions for the nix programming language
     Check(Check),
@@ -24,7 +24,7 @@ pub enum SubCommand {
     Explain(Explain),
 }
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 pub struct Check {
     /// File or directory to run check on
     #[clap(default_value = ".", parse(from_os_str))]
@@ -67,7 +67,7 @@ impl Check {
     }
 }
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 pub struct Fix {
     /// File or directory to run fix on
     #[clap(default_value = ".", parse(from_os_str))]
@@ -127,7 +127,7 @@ impl Fix {
     }
 }
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 pub struct Single {
     /// File to run single-fix on
     #[clap(parse(from_os_str))]
@@ -174,7 +174,7 @@ impl Single {
     }
 }
 
-#[derive(Clap, Debug)]
+#[derive(Parser, Debug)]
 pub struct Explain {
     /// Warning code to explain
     #[clap(parse(try_from_str = parse_warning_code))]
diff --git a/bin/src/lib.rs b/bin/src/lib.rs
new file mode 100644
index 0000000..49c1a41
--- /dev/null
+++ b/bin/src/lib.rs
@@ -0,0 +1,7 @@
+pub mod config;
+pub mod dirs;
+pub mod err;
+pub mod explain;
+pub mod fix;
+pub mod lint;
+pub mod traits;
diff --git a/bin/src/main.rs b/bin/src/main.rs
index fabc509..f504796 100644
--- a/bin/src/main.rs
+++ b/bin/src/main.rs
@@ -1,15 +1,9 @@
-mod config;
-mod dirs;
-mod err;
-mod explain;
-mod fix;
-mod lint;
-mod traits;
-
-use crate::err::StatixErr;
-
-use clap::Clap;
-use config::{Opts, SubCommand};
+use clap::Parser;
+use statix::{
+    config::{Opts, SubCommand},
+    err::StatixErr,
+    explain, fix, lint,
+};
 
 fn _main() -> Result<(), StatixErr> {
     let opts = Opts::parse();
diff --git a/bin/tests/data/bool_comparison.nix b/bin/tests/data/bool_comparison.nix
new file mode 100644
index 0000000..dee2d08
--- /dev/null
+++ b/bin/tests/data/bool_comparison.nix
@@ -0,0 +1,13 @@
+[
+  # trivial
+  (a == true)
+  (b == true)
+  (true == c)
+  (true == d)
+
+  # not equals
+  (e != true)
+  (f != false)
+  (true != g)
+  (false != h)
+]
diff --git a/bin/tests/data/collapsible_let_in.nix b/bin/tests/data/collapsible_let_in.nix
new file mode 100644
index 0000000..7b41014
--- /dev/null
+++ b/bin/tests/data/collapsible_let_in.nix
@@ -0,0 +1,9 @@
+let
+  a = 2;
+  b = 3;
+in
+  let
+    c = 5;
+    d = 6;
+  in
+  a + b + c + d
diff --git a/bin/tests/data/deprecated_is_null.nix b/bin/tests/data/deprecated_is_null.nix
new file mode 100644
index 0000000..42596d7
--- /dev/null
+++ b/bin/tests/data/deprecated_is_null.nix
@@ -0,0 +1,6 @@
+let
+  e = null;
+in
+if isNull e
+then "no"
+else "yes"
diff --git a/bin/tests/data/empty_let_in.nix b/bin/tests/data/empty_let_in.nix
new file mode 100644
index 0000000..3ecb6e4
--- /dev/null
+++ b/bin/tests/data/empty_let_in.nix
@@ -0,0 +1,3 @@
+let
+in
+  null
diff --git a/bin/tests/data/empty_pattern.nix b/bin/tests/data/empty_pattern.nix
new file mode 100644
index 0000000..23d99e8
--- /dev/null
+++ b/bin/tests/data/empty_pattern.nix
@@ -0,0 +1,9 @@
+[
+  # match
+  ({ ... }: 42)
+
+  # don't match
+  ({ a, ... }: a)
+  ({ ... } @ inputs: inputs)
+]
+
diff --git a/bin/tests/data/eta_reduction.nix b/bin/tests/data/eta_reduction.nix
new file mode 100644
index 0000000..e717ee7
--- /dev/null
+++ b/bin/tests/data/eta_reduction.nix
@@ -0,0 +1,18 @@
+let
+  double = x: x * 2;
+  inherit (builtins) map;
+  xs = [ 1 2 3 ];
+  f = {
+    inherit double;
+    val = 2;
+  };
+in
+[
+  (map (x: double x) xs)
+
+  # don't lint on non-free exprs
+  (map (f: f.double f.val) [ f ])
+
+  # other non-free forms
+  (map (f: {inherit f;}.double f.val) [ f ])
+]
diff --git a/bin/tests/data/legacy_let_syntax.nix b/bin/tests/data/legacy_let_syntax.nix
new file mode 100644
index 0000000..46e3191
--- /dev/null
+++ b/bin/tests/data/legacy_let_syntax.nix
@@ -0,0 +1,5 @@
+let {
+  body = x + y;
+  x = "hello,";
+  y = " world!";
+}
diff --git a/bin/tests/data/manual_inherit.nix b/bin/tests/data/manual_inherit.nix
new file mode 100644
index 0000000..53ae4d7
--- /dev/null
+++ b/bin/tests/data/manual_inherit.nix
@@ -0,0 +1,12 @@
+let
+  a = 2;
+  y = "y";
+in
+{
+  # trivial
+  a = a;
+
+  # don't lint
+  x.y = y;
+}
+
diff --git a/bin/tests/data/manual_inherit_from.nix b/bin/tests/data/manual_inherit_from.nix
new file mode 100644
index 0000000..214b2a3
--- /dev/null
+++ b/bin/tests/data/manual_inherit_from.nix
@@ -0,0 +1,8 @@
+let
+  a = {b = 2; c = 3;};
+in
+{
+  b = a.b;
+  c = a.c;
+}
+
diff --git a/bin/tests/data/redundant_pattern_bind.nix b/bin/tests/data/redundant_pattern_bind.nix
new file mode 100644
index 0000000..d328c50
--- /dev/null
+++ b/bin/tests/data/redundant_pattern_bind.nix
@@ -0,0 +1 @@
+{ ... }  @ inputs: null
diff --git a/bin/tests/data/unquoted_splices.nix b/bin/tests/data/unquoted_splices.nix
new file mode 100644
index 0000000..30935b0
--- /dev/null
+++ b/bin/tests/data/unquoted_splices.nix
@@ -0,0 +1,15 @@
+let
+  x = 2;
+  y = 3;
+  a = { "2" = y; };
+in
+[
+  ${x}
+  ${toString (x + y)}
+  a.${toString x}
+
+  # multiline test
+  ${
+    toString x
+  }
+]
diff --git a/bin/tests/data/unquoted_uri.nix b/bin/tests/data/unquoted_uri.nix
new file mode 100644
index 0000000..e56574a
--- /dev/null
+++ b/bin/tests/data/unquoted_uri.nix
@@ -0,0 +1 @@
+github:nerdypepper/statix
diff --git a/bin/tests/data/useless_parens.nix b/bin/tests/data/useless_parens.nix
new file mode 100644
index 0000000..cf26441
--- /dev/null
+++ b/bin/tests/data/useless_parens.nix
@@ -0,0 +1,16 @@
+let
+  # parens around primitives
+  a = {
+    b = ("hello");
+    c = (d);
+    e = ({ f = 2; });
+  };
+
+  # parens around let-value
+  g = (1 + 2);
+  h = ({ inherit i; });
+
+  # TODO: binary exprs, function args etc.
+in
+  # parens around let body
+  (null)
diff --git a/bin/tests/main.rs b/bin/tests/main.rs
new file mode 100644
index 0000000..6175c90
--- /dev/null
+++ b/bin/tests/main.rs
@@ -0,0 +1,47 @@
+mod util {
+    #[macro_export]
+    macro_rules! test_lint {
+        ($($tname:ident),*,) => {
+            test_lint!($($tname),*);
+        };
+        ($($tname:ident),*) => {
+            $(
+                #[test]
+                fn $tname() {
+                    use statix::{config::OutFormat, traits::WriteDiagnostic, lint};
+                    use vfs::ReadOnlyVfs;
+
+                    let file_path = concat!("data/", stringify!($tname), ".nix");
+                    let contents = include_str!(concat!("data/", stringify!($tname), ".nix"));
+
+                    let vfs = ReadOnlyVfs::singleton(file_path, contents.as_bytes());
+
+                    let mut buffer = Vec::new();
+                    vfs.iter().map(lint::lint).for_each(|r| {
+                        buffer.write(&r, &vfs, OutFormat::StdErr).unwrap();
+                    });
+
+                    let stripped = strip_ansi_escapes::strip(&buffer).unwrap();
+                    let out =  std::str::from_utf8(&stripped).unwrap();
+                    insta::assert_snapshot!(&out);
+                }
+            )*
+        };
+    }
+}
+
+test_lint! {
+    bool_comparison,
+    empty_let_in,
+    manual_inherit,
+    manual_inherit_from,
+    legacy_let_syntax,
+    collapsible_let_in,
+    eta_reduction,
+    useless_parens,
+    unquoted_splices,
+    empty_pattern,
+    redundant_pattern_bind,
+    unquoted_uri,
+    deprecated_is_null,
+}
diff --git a/bin/tests/snapshots/main__bool_comparison.snap b/bin/tests/snapshots/main__bool_comparison.snap
new file mode 100644
index 0000000..0865332
--- /dev/null
+++ b/bin/tests/snapshots/main__bool_comparison.snap
@@ -0,0 +1,62 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W01] Warning: Unnecessary comparison with boolean
+   ╭─[data/bool_comparison.nix:3:4]
+   │
+ 3 │   (a == true)
+   ·    ────┬────  
+   ·        ╰────── Comparing a with boolean literal true
+───╯
+[W01] Warning: Unnecessary comparison with boolean
+   ╭─[data/bool_comparison.nix:4:4]
+   │
+ 4 │   (b == true)
+   ·    ────┬────  
+   ·        ╰────── Comparing b with boolean literal true
+───╯
+[W01] Warning: Unnecessary comparison with boolean
+   ╭─[data/bool_comparison.nix:5:4]
+   │
+ 5 │   (true == c)
+   ·    ────┬────  
+   ·        ╰────── Comparing c with boolean literal true
+───╯
+[W01] Warning: Unnecessary comparison with boolean
+   ╭─[data/bool_comparison.nix:6:4]
+   │
+ 6 │   (true == d)
+   ·    ────┬────  
+   ·        ╰────── Comparing d with boolean literal true
+───╯
+[W01] Warning: Unnecessary comparison with boolean
+   ╭─[data/bool_comparison.nix:9:4]
+   │
+ 9 │   (e != true)
+   ·    ────┬────  
+   ·        ╰────── Comparing e with boolean literal true
+───╯
+[W01] Warning: Unnecessary comparison with boolean
+    ╭─[data/bool_comparison.nix:10:4]
+    │
+ 10 │   (f != false)
+    ·    ─────┬────  
+    ·         ╰────── Comparing f with boolean literal false
+────╯
+[W01] Warning: Unnecessary comparison with boolean
+    ╭─[data/bool_comparison.nix:11:4]
+    │
+ 11 │   (true != g)
+    ·    ────┬────  
+    ·        ╰────── Comparing g with boolean literal true
+────╯
+[W01] Warning: Unnecessary comparison with boolean
+    ╭─[data/bool_comparison.nix:12:4]
+    │
+ 12 │   (false != h)
+    ·    ─────┬────  
+    ·         ╰────── Comparing h with boolean literal false
+────╯
+
diff --git a/bin/tests/snapshots/main__collapsible_let_in.snap b/bin/tests/snapshots/main__collapsible_let_in.snap
new file mode 100644
index 0000000..b135abc
--- /dev/null
+++ b/bin/tests/snapshots/main__collapsible_let_in.snap
@@ -0,0 +1,17 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W06] Warning: These let-in expressions are collapsible
+   ╭─[data/collapsible_let_in.nix:1:1]
+   │
+ 1 │ ╭───▶ let
+ 5 │ │ ╭─▶   let
+ 9 │ │ ├─▶   a + b + c + d
+   · │ │                 │   
+   · │ ╰───────────────────── This let in expression is nested
+   · │                   │   
+   · ╰───────────────────┴─── This let in expression contains a nested let in expression
+───╯
+
diff --git a/bin/tests/snapshots/main__deprecated_is_null.snap b/bin/tests/snapshots/main__deprecated_is_null.snap
new file mode 100644
index 0000000..d49b381
--- /dev/null
+++ b/bin/tests/snapshots/main__deprecated_is_null.snap
@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W13] Warning: Found usage of deprecated builtin isNull
+   ╭─[data/deprecated_is_null.nix:4:4]
+   │
+ 4 │ if isNull e
+   ·    ────┬───  
+   ·        ╰───── isNull is deprecated, check equality with null instead
+───╯
+
diff --git a/bin/tests/snapshots/main__empty_let_in.snap b/bin/tests/snapshots/main__empty_let_in.snap
new file mode 100644
index 0000000..426692f
--- /dev/null
+++ b/bin/tests/snapshots/main__empty_let_in.snap
@@ -0,0 +1,14 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W02] Warning: Useless let-in expression
+   ╭─[data/empty_let_in.nix:1:1]
+   │
+ 1 │ ╭─▶ let
+ 3 │ ├─▶   null
+   · │            
+   · ╰──────────── This let-in expression has no entries
+───╯
+
diff --git a/bin/tests/snapshots/main__empty_pattern.snap b/bin/tests/snapshots/main__empty_pattern.snap
new file mode 100644
index 0000000..3ea7ae0
--- /dev/null
+++ b/bin/tests/snapshots/main__empty_pattern.snap
@@ -0,0 +1,20 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W10] Warning: Found empty pattern in function argument
+   ╭─[data/empty_pattern.nix:3:4]
+   │
+ 3 │   ({ ... }: 42)
+   ·    ───┬───  
+   ·       ╰───── This pattern is empty, use _ instead
+───╯
+[W11] Warning: Found redundant pattern bind in function argument
+   ╭─[data/empty_pattern.nix:7:4]
+   │
+ 7 │   ({ ... } @ inputs: inputs)
+   ·    ────────┬───────  
+   ·            ╰───────── This pattern bind is redundant, use inputs instead
+───╯
+
diff --git a/bin/tests/snapshots/main__eta_reduction.snap b/bin/tests/snapshots/main__eta_reduction.snap
new file mode 100644
index 0000000..6271980
--- /dev/null
+++ b/bin/tests/snapshots/main__eta_reduction.snap
@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W07] Warning: This function expression is eta reducible
+    ╭─[data/eta_reduction.nix:11:9]
+    │
+ 11 │   (map (x: double x) xs)
+    ·         ─────┬─────  
+    ·              ╰─────── Found eta-reduction: double
+────╯
+
diff --git a/bin/tests/snapshots/main__legacy_let_syntax.snap b/bin/tests/snapshots/main__legacy_let_syntax.snap
new file mode 100644
index 0000000..35aa7ee
--- /dev/null
+++ b/bin/tests/snapshots/main__legacy_let_syntax.snap
@@ -0,0 +1,14 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W05] Warning: Using undocumented `let` syntax
+   ╭─[data/legacy_let_syntax.nix:1:1]
+   │
+ 1 │ ╭─▶ let {
+ 5 │ ├─▶ }
+   · │       
+   · ╰─────── Prefer rec over undocumented let syntax
+───╯
+
diff --git a/bin/tests/snapshots/main__manual_inherit.snap b/bin/tests/snapshots/main__manual_inherit.snap
new file mode 100644
index 0000000..063867c
--- /dev/null
+++ b/bin/tests/snapshots/main__manual_inherit.snap
@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W03] Warning: Assignment instead of inherit
+   ╭─[data/manual_inherit.nix:7:3]
+   │
+ 7 │   a = a;
+   ·   ───┬──  
+   ·      ╰──── This assignment is better written with inherit
+───╯
+
diff --git a/bin/tests/snapshots/main__manual_inherit_from.snap b/bin/tests/snapshots/main__manual_inherit_from.snap
new file mode 100644
index 0000000..9cf1f5d
--- /dev/null
+++ b/bin/tests/snapshots/main__manual_inherit_from.snap
@@ -0,0 +1,20 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W04] Warning: Assignment instead of inherit from
+   ╭─[data/manual_inherit_from.nix:5:3]
+   │
+ 5 │   b = a.b;
+   ·   ────┬───  
+   ·       ╰───── This assignment is better written with inherit
+───╯
+[W04] Warning: Assignment instead of inherit from
+   ╭─[data/manual_inherit_from.nix:6:3]
+   │
+ 6 │   c = a.c;
+   ·   ────┬───  
+   ·       ╰───── This assignment is better written with inherit
+───╯
+
diff --git a/bin/tests/snapshots/main__redundant_pattern_bind.snap b/bin/tests/snapshots/main__redundant_pattern_bind.snap
new file mode 100644
index 0000000..2f26818
--- /dev/null
+++ b/bin/tests/snapshots/main__redundant_pattern_bind.snap
@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W11] Warning: Found redundant pattern bind in function argument
+   ╭─[data/redundant_pattern_bind.nix:1:1]
+   │
+ 1 │ { ... }  @ inputs: null
+   · ────────┬────────  
+   ·         ╰────────── This pattern bind is redundant, use inputs instead
+───╯
+
diff --git a/bin/tests/snapshots/main__unquoted_splices.snap b/bin/tests/snapshots/main__unquoted_splices.snap
new file mode 100644
index 0000000..5fd1917
--- /dev/null
+++ b/bin/tests/snapshots/main__unquoted_splices.snap
@@ -0,0 +1,35 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W09] Warning: Found unquoted splice expression
+   ╭─[data/unquoted_splices.nix:7:3]
+   │
+ 7 │   ${x}
+   ·   ──┬─  
+   ·     ╰─── Consider quoting this splice expression
+───╯
+[W09] Warning: Found unquoted splice expression
+   ╭─[data/unquoted_splices.nix:8:3]
+   │
+ 8 │   ${toString (x + y)}
+   ·   ─────────┬─────────  
+   ·            ╰─────────── Consider quoting this splice expression
+───╯
+[W09] Warning: Found unquoted splice expression
+   ╭─[data/unquoted_splices.nix:9:5]
+   │
+ 9 │   a.${toString x}
+   ·     ──────┬──────  
+   ·           ╰──────── Consider quoting this splice expression
+───╯
+[W09] Warning: Found unquoted splice expression
+    ╭─[data/unquoted_splices.nix:12:3]
+    │
+ 12 │ ╭─▶   ${
+ 14 │ ├─▶   }
+    · │         
+    · ╰───────── Consider quoting this splice expression
+────╯
+
diff --git a/bin/tests/snapshots/main__unquoted_uri.snap b/bin/tests/snapshots/main__unquoted_uri.snap
new file mode 100644
index 0000000..2f0e5a9
--- /dev/null
+++ b/bin/tests/snapshots/main__unquoted_uri.snap
@@ -0,0 +1,13 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W12] Warning: Found unquoted URI expression
+   ╭─[data/unquoted_uri.nix:1:1]
+   │
+ 1 │ github:nerdypepper/statix
+   · ────────────┬────────────  
+   ·             ╰────────────── Consider quoting this URI expression
+───╯
+
diff --git a/bin/tests/snapshots/main__useless_parens.snap b/bin/tests/snapshots/main__useless_parens.snap
new file mode 100644
index 0000000..d44176e
--- /dev/null
+++ b/bin/tests/snapshots/main__useless_parens.snap
@@ -0,0 +1,48 @@
+---
+source: bin/tests/main.rs
+expression: "&out"
+
+---
+[W08] Warning: These parentheses can be omitted
+    ╭─[data/useless_parens.nix:16:3]
+    │
+ 16 │   (null)
+    ·   ───┬──  
+    ·      ╰──── Useless parentheses around body of let expression
+────╯
+[W08] Warning: These parentheses can be omitted
+   ╭─[data/useless_parens.nix:4:9]
+   │
+ 4 │     b = ("hello");
+   ·         ────┬────  
+   ·             ╰────── Useless parentheses around value in binding
+───╯
+[W08] Warning: These parentheses can be omitted
+   ╭─[data/useless_parens.nix:5:9]
+   │
+ 5 │     c = (d);
+   ·         ─┬─  
+   ·          ╰─── Useless parentheses around value in binding
+───╯
+[W08] Warning: These parentheses can be omitted
+   ╭─[data/useless_parens.nix:6:9]
+   │
+ 6 │     e = ({ f = 2; });
+   ·         ──────┬─────  
+   ·               ╰─────── Useless parentheses around value in binding
+───╯
+[W08] Warning: These parentheses can be omitted
+    ╭─[data/useless_parens.nix:10:7]
+    │
+ 10 │   g = (1 + 2);
+    ·       ───┬───  
+    ·          ╰───── Useless parentheses around value in binding
+────╯
+[W08] Warning: These parentheses can be omitted
+    ╭─[data/useless_parens.nix:11:7]
+    │
+ 11 │   h = ({ inherit i; });
+    ·       ────────┬───────  
+    ·               ╰───────── Useless parentheses around value in binding
+────╯
+
diff --git a/flake.nix b/flake.nix
index 3b9d011..b166817 100644
--- a/flake.nix
+++ b/flake.nix
@@ -93,11 +93,12 @@
             "clippy"
             "rust-src"
           ];
+          inherit (fenix.packages."${system}") rust-analyzer;
         in
-        with pkgs;
-        mkShell rec {
+        pkgs.mkShell {
           nativeBuildInputs = [
-            cargo-watch
+            pkgs.cargo-watch
+            pkgs.cargo-insta
             rust-analyzer
             toolchain
           ];
diff --git a/lib/src/lints/useless_parens.rs b/lib/src/lints/useless_parens.rs
index 45d80ae..dccc717 100644
--- a/lib/src/lints/useless_parens.rs
+++ b/lib/src/lints/useless_parens.rs
@@ -3,7 +3,7 @@ use crate::{Diagnostic, Metadata, Report, Rule, Suggestion};
 use if_chain::if_chain;
 use macros::lint;
 use rnix::{
-    types::{KeyValue, Paren, ParsedType, TypedNode, Wrapper},
+    types::{KeyValue, LetIn, Paren, ParsedType, TypedNode, Wrapper},
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
@@ -71,7 +71,7 @@ fn do_thing(parsed_type_node: ParsedType) -> Option<Diagnostic> {
             if let Some(inner) = value_in_parens.inner();
             then {
                 let at = value_range;
-                let message = "Useless parentheses around value in `let` binding";
+                let message = "Useless parentheses around value in binding";
                 let replacement = inner;
                 Some(Diagnostic::suggest(at, message, Suggestion::new(at, replacement)))
             } else {
@@ -98,7 +98,11 @@ fn do_thing(parsed_type_node: ParsedType) -> Option<Diagnostic> {
 
             // ensure that we don't lint inside let-in statements
             // we already lint such cases in previous match stmt
-            if KeyValue::cast(father_node).is_none();
+            if KeyValue::cast(father_node.clone()).is_none();
+
+            // ensure that we don't lint inside let-bodies
+            // if this primitive is a let-body, we have already linted it
+            if LetIn::cast(father_node).is_none();
 
             if let Some(inner_node) = paren_expr.inner();
             if let Some(parsed_inner) = ParsedType::cast(inner_node);
diff --git a/vfs/src/lib.rs b/vfs/src/lib.rs
index 8b5df79..cd6cc03 100644
--- a/vfs/src/lib.rs
+++ b/vfs/src/lib.rs
@@ -7,7 +7,7 @@ use std::{
 use indexmap::IndexSet;
 
 #[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Eq, Ord, Hash)]
-pub struct FileId(u32);
+pub struct FileId(pub u32);
 
 #[derive(Debug, Default)]
 pub struct Interner {