add explainations to each lint

13 files changed, 265 insertions, 26 deletions

diff --git a/bin/src/main.rs b/bin/src/main.rs
index 138b243..31f6823 100644
--- a/bin/src/main.rs
+++ b/bin/src/main.rs
@@ -88,8 +88,8 @@ fn _main() -> Result<(), StatixErr> {
             }
         }
         SubCommand::Explain(explain_config) => {
-            let explaination = explain::explain(explain_config.target)?;
-            println!("{}", explaination);
+            let explanation = explain::explain(explain_config.target)?;
+            println!("{}", explanation)
         }
     }
     Ok(())
diff --git a/lib/src/lints/bool_comparison.rs b/lib/src/lints/bool_comparison.rs
index 6636faf..5c9bee8 100644
--- a/lib/src/lints/bool_comparison.rs
+++ b/lib/src/lints/bool_comparison.rs
@@ -7,28 +7,25 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode,
 };
 
-/// What it does
-/// ------------
-/// Checks for expressions of the form x == true, x != true and
+/// ## What it does
+/// Checks for expressions of the form `x == true`, `x != true` and
 /// suggests using the variable directly.
 ///
-/// Why is this bad?
-/// ----------------
+/// ## Why is this bad?
 /// Unnecessary code.
 ///
-/// Example
-/// --------
-/// Instead of checking the value of x:
+/// ## Example
+/// Instead of checking the value of `x`:
 ///
-///     if x == true
-///     then 0
-///     else 1
+/// ```
+/// if x == true then 0 else 1
+/// ```
 ///
-/// Use x directly:
+/// Use `x` directly:
 ///
-///     if x
-///     then 0
-///     else 1
+/// ```
+/// if x then 0 else 1
+/// ```
 #[lint(
     name = "bool_comparison",
     note = "Unnecessary comparison with boolean",
diff --git a/lib/src/lints/collapsible_let_in.rs b/lib/src/lints/collapsible_let_in.rs
index cb76c37..21199a8 100644
--- a/lib/src/lints/collapsible_let_in.rs
+++ b/lib/src/lints/collapsible_let_in.rs
@@ -8,6 +8,34 @@ use rnix::{
 };
 use rowan::Direction;
 
+/// ## What it does
+/// Checks for `let-in` expressions whose body is another `let-in`
+/// expression.
+///
+/// ## Why is this bad?
+/// Unnecessary code, the `let-in` expressions can be merged.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   a = 2;
+/// in
+/// let
+///   b = 3;
+/// in
+///   a + b
+/// ```
+///
+/// Merge both `let-in` expressions:
+///
+/// ```
+/// let
+///   a = 2;
+///   b = 3;
+/// in
+///   a + b
+/// ```
 #[lint(
     name = "collapsible let in",
     note = "These let-in expressions are collapsible",
diff --git a/lib/src/lints/empty_let_in.rs b/lib/src/lints/empty_let_in.rs
index 4e0887d..b255c23 100644
--- a/lib/src/lints/empty_let_in.rs
+++ b/lib/src/lints/empty_let_in.rs
@@ -7,7 +7,24 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
-/// empty let-in found
+/// ## What it does
+/// Checks for `let-in` expressions which create no new bindings.
+///
+/// ## Why is this bad?
+/// `let-in` expressions that create no new bindings are useless.
+/// These are probably remnants from debugging or editing expressions.
+///
+/// ## Example
+///
+/// ```
+/// let in pkgs.statix
+/// ```
+///
+/// Preserve only the body of the `let-in` expression:
+///
+/// ```
+/// pkgs.statix
+/// ```
 #[lint(
     name = "empty let-in",
     note = "Useless let-in expression",
diff --git a/lib/src/lints/empty_pattern.rs b/lib/src/lints/empty_pattern.rs
index ef47c69..5312548 100644
--- a/lib/src/lints/empty_pattern.rs
+++ b/lib/src/lints/empty_pattern.rs
@@ -7,6 +7,33 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for an empty variadic pattern: `{...}`, in a function
+/// argument.
+///
+/// ## Why is this bad?
+/// The intention with empty patterns is not instantly obvious. Prefer
+/// an underscore identifier instead, to indicate that the argument
+/// is being ignored.
+///
+/// ## Example
+///
+/// ```
+/// client = { ... }: {
+///   imports = [ self.nixosModules.irmaseal-pkg ];
+///   services.irmaseal-pkg.enable = true;
+/// };
+/// ```
+///
+/// Replace the empty variadic pattern with `_` to indicate that you
+/// intend to ignore the argument:
+///
+/// ```
+/// client = _: {
+///   imports = [ self.nixosModules.irmaseal-pkg ];
+///   services.irmaseal-pkg.enable = true;
+/// };
+/// ```
 #[lint(
     name = "empty pattern",
     note = "Found empty pattern in function argument",
diff --git a/lib/src/lints/eta_reduction.rs b/lib/src/lints/eta_reduction.rs
index b329ae8..3a483d0 100644
--- a/lib/src/lints/eta_reduction.rs
+++ b/lib/src/lints/eta_reduction.rs
@@ -7,6 +7,32 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode,
 };
 
+/// ## What it does
+/// Checks for eta-reducible functions, i.e.: converts lambda
+/// expressions into free standing functions where applicable.
+///
+/// ## Why is this bad?
+/// Oftentimes, eta-reduction results in code that is more natural
+/// to read.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   double = i: 2 * i;
+/// in
+/// map (x: double x) [ 1 2 3 ]
+/// ```
+///
+/// The lambda passed to the `map` function is eta-reducible, and the
+/// result reads more naturally:
+///
+/// ```
+/// let
+///   double = i: 2 * i;
+/// in
+/// map double [ 1 2 3 ]
+/// ```
 #[lint(
     name = "eta reduction",
     note = "This function expression is eta reducible",
diff --git a/lib/src/lints/legacy_let_syntax.rs b/lib/src/lints/legacy_let_syntax.rs
index 8b37df8..139f633 100644
--- a/lib/src/lints/legacy_let_syntax.rs
+++ b/lib/src/lints/legacy_let_syntax.rs
@@ -7,6 +7,34 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for legacy-let syntax that was never formalized.
+///
+/// ## Why is this bad?
+/// This syntax construct is undocumented, refrain from using it.
+///
+/// ## Example
+///
+/// Legacy let syntax makes use of an attribute set annotated with
+/// `let` and expects a `body` attribute.
+/// ```
+/// let {
+///   body = x + y;
+///   x = 2;
+///   y = 3;
+/// }
+/// ```
+///
+/// This is trivially representible via `rec`, which is documented
+/// and more widely known:
+///
+/// ```
+/// rec {
+///   body = x + y;
+///   x = 2;
+///   y = 3;
+/// }.body
+/// ```
 #[lint(
     name = "legacy let syntax",
     note = "Using undocumented `let` syntax",
diff --git a/lib/src/lints/manual_inherit.rs b/lib/src/lints/manual_inherit.rs
index 1c10cbf..2d119c3 100644
--- a/lib/src/lints/manual_inherit.rs
+++ b/lib/src/lints/manual_inherit.rs
@@ -7,6 +7,30 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for bindings of the form `a = a`.
+///
+/// ## Why is this bad?
+/// If the aim is to bring attributes from a larger scope into
+/// the current scope, prefer an inherit statement.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   a = 2;
+/// in
+///   { a = a; b = 3; }
+/// ```
+///
+/// Try `inherit` instead:
+///
+/// ```
+/// let
+///   a = 2;
+/// in
+///   { inherit a; b = 3; }
+/// ```
 #[lint(
     name = "manual inherit",
     note = "Assignment instead of inherit",
diff --git a/lib/src/lints/manual_inherit_from.rs b/lib/src/lints/manual_inherit_from.rs
index 146d55b..8d0f539 100644
--- a/lib/src/lints/manual_inherit_from.rs
+++ b/lib/src/lints/manual_inherit_from.rs
@@ -7,6 +7,30 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for bindings of the form `a = someAttr.a`.
+///
+/// ## Why is this bad?
+/// If the aim is to extract or bring attributes of an attrset into
+/// scope, prefer an inherit statement.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   mtl = pkgs.haskellPackages.mtl;
+/// in
+///   null
+/// ```
+///
+/// Try `inherit` instead:
+///
+/// ```
+/// let
+///   inherit (pkgs.haskellPackages) mtl;
+/// in
+///   null
+/// ```
 #[lint(
     name = "manual inherit from",
     note = "Assignment instead of inherit from",
diff --git a/lib/src/lints/redundant_pattern_bind.rs b/lib/src/lints/redundant_pattern_bind.rs
index ad1aba8..5b0711f 100644
--- a/lib/src/lints/redundant_pattern_bind.rs
+++ b/lib/src/lints/redundant_pattern_bind.rs
@@ -7,10 +7,29 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for binds of the form `inputs @ { ... }` in function
+/// arguments.
+///
+/// ## Why is this bad?
+/// The variadic pattern here is redundant, as it does not capture
+/// anything.
+///
+/// ## Example
+///
+/// ```
+/// inputs @ { ... }: inputs.nixpkgs
+/// ```
+///
+/// Remove the pattern altogether:
+///
+/// ```
+/// inputs: inputs.nixpkgs
+/// ```
 #[lint(
     name = "redundant pattern bind",
     note = "Found redundant pattern bind in function argument",
-    code = 10,
+    code = 11,
     match_with = SyntaxKind::NODE_PATTERN
 )]
 struct RedundantPatternBind;
diff --git a/lib/src/lints/unquoted_splice.rs b/lib/src/lints/unquoted_splice.rs
index 2831c1b..c2fd6e4 100644
--- a/lib/src/lints/unquoted_splice.rs
+++ b/lib/src/lints/unquoted_splice.rs
@@ -7,6 +7,30 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for antiquote/splice expressions that are not quoted.
+///
+/// ## Why is this bad?
+/// An *anti*quoted expression should always occur within a *quoted*
+/// expression.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   pkgs = nixpkgs.legacyPackages.${system};
+/// in
+///   pkgs
+/// ```
+///
+/// Quote the splice expression:
+///
+/// ```
+/// let
+///   pkgs = nixpkgs.legacyPackages."${system}";
+/// in
+///   pkgs
+/// ```
 #[lint(
     name = "unquoted splice",
     note = "Found unquoted splice expression",
diff --git a/lib/src/lints/useless_parens.rs b/lib/src/lints/useless_parens.rs
index 9dfeabb..36ad1b7 100644
--- a/lib/src/lints/useless_parens.rs
+++ b/lib/src/lints/useless_parens.rs
@@ -7,6 +7,31 @@ use rnix::{
     NodeOrToken, SyntaxElement, SyntaxKind,
 };
 
+/// ## What it does
+/// Checks for unnecessary parentheses.
+///
+/// ## Why is this bad?
+/// Unnecessarily parenthesized code is hard to read.
+///
+/// ## Example
+///
+/// ```
+/// let
+///   double = (x: 2 * x);
+///   ls = map (double) [ 1 2 3 ];
+/// in
+///   (2 + 3)
+/// ```
+///
+/// Remove unnecessary parentheses:
+///
+/// ```
+/// let
+///   double = x: 2 * x;
+///   ls = map double [ 1 2 3 ];
+/// in
+///   2 + 3
+/// ```
 #[lint(
     name = "useless parens",
     note = "These parentheses can be omitted",
diff --git a/macros/src/explain.rs b/macros/src/explain.rs
index 8b00740..9bc3c29 100644
--- a/macros/src/explain.rs
+++ b/macros/src/explain.rs
@@ -7,15 +7,15 @@ pub fn generate_explain_impl(struct_item: &ItemStruct) -> TokenStream2 {
     let explain = struct_item
         .attrs
         .iter()
-        .filter_map(|a| a.parse_meta().ok())
-        .filter_map(|meta| match meta {
-            Meta::NameValue(MetaNameValue { path, lit, .. }) if path.is_ident("doc") => Some(lit),
-            _ => None,
-        })
-        .filter_map(|lit| match lit {
-            Lit::Str(str_lit) => Some(str_lit.value()),
+        .filter_map(|attr| match attr.parse_meta().ok() {
+            Some(Meta::NameValue(MetaNameValue {
+                path,
+                lit: Lit::Str(str_lit),
+                ..
+            })) if path.is_ident("doc") => Some(str_lit.value()),
             _ => None,
         })
+        .map(|s| s.strip_prefix(' ').unwrap_or(&s).to_owned())
         .collect::<Vec<_>>()
         .join("\n");
     quote! {