chore: [#969] add strict clippy lints and fix all violations (#1405)

## Summary

- Adds `[workspace.lints.clippy]` to root `Cargo.toml` with 31
deny-level lints (style, complexity, pedantic code quality)
- Adds `[lints] workspace = true` to all crate `Cargo.toml` files
- Fixes all violations across 89 files: merged identical match arms,
rewrote `if let / else return` as `let...else`, removed redundant
`continue`s, replaced wildcard `_` match arms with explicit variants,
converted `needless_pass_by_value` params to borrowed types, unwrapped
`unnecessary_wraps`, and added `#[allow]` on legitimately large compiler
functions

Closes #969

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: milkyskies <milkyskies>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: milkyskies

Cargo.toml

@@ -32,6 +32,37 @@ tokio = { version = "1.52.0", features = ["full"] }
 tower-lsp = "0.20.0"
 insta = "1.47.2"
 
+[workspace.lints.clippy]
+# ── Style ──
+collapsible_if = "deny"
+collapsible_else_if = "deny"
+needless_bool = "deny"
+needless_return = "deny"
+redundant_else = "deny"
+manual_let_else = "deny"
+unnested_or_patterns = "deny"
+single_match_else = "deny"
+fn_params_excessive_bools = "deny"
+struct_excessive_bools = "deny"
+
+# ── Complexity ──
+cognitive_complexity = "deny"
+too_many_lines = "deny"
+match_same_arms = "deny"
+
+# ── Code quality (pedantic) ──
+redundant_closure = "deny"
+needless_pass_by_value = "deny"
+wildcard_imports = "deny"
+manual_string_new = "deny"
+uninlined_format_args = "deny"
+needless_continue = "deny"
+cast_lossless = "deny"
+explicit_iter_loop = "deny"
+unused_self = "deny"
+unnecessary_wraps = "deny"
+match_wildcard_for_single_variants = "deny"
+
 # CI profile: drop opt-level overrides so compile is fast.
 [profile.ci]
 inherits = "dev"

crates/floe-cli/Cargo.toml

@@ -22,3 +22,6 @@ anyhow.workspace = true
 clap.workspace = true
 notify.workspace = true
 tokio.workspace = true
+
+[lints]
+workspace = true

crates/floe-cli/src/main.rs

@@ -361,6 +361,7 @@ fn cmd_check(path: &Path) -> Result<()> {
 
 // ── Test ─────────────────────────────────────────────────────────
 
+#[allow(clippy::too_many_lines)]
 fn cmd_test(path: &Path) -> Result<()> {
     let files = discover_fl_files(path)?;
     if files.is_empty() {
@@ -456,15 +457,12 @@ fn cmd_test(path: &Path) -> Result<()> {
                 std::process::Command::new(runner).arg(&temp_file).status()
             };
 
-            match result {
-                Ok(status) => {
-                    if !status.success() {
-                        errors += 1;
-                    }
-                    ran = true;
-                    break;
+            if let Ok(status) = result {
+                if !status.success() {
+                    errors += 1;
                 }
-                Err(_) => continue,
+                ran = true;
+                break;
             }
         }
 

crates/floe-core/Cargo.toml

@@ -34,3 +34,6 @@ xxhash-rust = { version = "0.8.15", features = ["xxh3"] }
 [dev-dependencies]
 insta.workspace = true
 tempfile.workspace = true
+
+[lints]
+workspace = true

crates/floe-core/src/checker.rs

@@ -96,8 +96,9 @@ pub(crate) fn body_has_promise_await<T>(expr: &Expr<T>) -> bool {
                         Arg::Positional(e) | Arg::Named { value: e, .. } => walk(e),
                     })
             }
-            ExprKind::Pipe { left, right } => walk(left) || walk(right),
-            ExprKind::Binary { left, right, .. } => walk(left) || walk(right),
+            ExprKind::Pipe { left, right } | ExprKind::Binary { left, right, .. } => {
+                walk(left) || walk(right)
+            }
             ExprKind::Member { object, .. } => walk(object),
             ExprKind::Unary { operand, .. }
             | ExprKind::Grouped(operand)
@@ -108,7 +109,7 @@ pub(crate) fn body_has_promise_await<T>(expr: &Expr<T>) -> bool {
                 match &item.kind {
                     ItemKind::Expr(e) => walk(e),
                     ItemKind::Const(c) => walk(&c.value),
-                    ItemKind::Function(_) => false, // don't descend into nested functions
+                    // don't descend into nested functions
                     _ => false,
                 }
             }),
@@ -117,7 +118,6 @@ pub(crate) fn body_has_promise_await<T>(expr: &Expr<T>) -> bool {
             }
             ExprKind::Array(items) | ExprKind::Tuple(items) => items.iter().any(walk),
             // Don't recurse into nested arrows — they're separate async contexts
-            ExprKind::Arrow { .. } => false,
             _ => false,
         }
     }
@@ -127,7 +127,14 @@ pub(crate) fn body_has_promise_await<T>(expr: &Expr<T>) -> bool {
 use crate::diagnostic::Diagnostic;
 use crate::interop::{self, DtsExport};
 use crate::lexer::span::Span;
-use crate::parser::ast::*;
+use crate::parser::ast::{
+    Arg, BinOp, ConstBinding, ConstDecl, DefaultExportDecl, Expr, ExprKind, ForBlock, FunctionDecl,
+    ImportDecl, Item, ItemKind, JsxChild, JsxElement, JsxElementKind, JsxProp, LiteralPattern,
+    MatchArm, ObjectDestructureField, Param, ParamDestructure, Pattern, PatternKind, Program,
+    RecordEntry, RecordField, StringPatternSegment, TemplatePart, TestBlock, TestStatement,
+    TraitDecl, TypeDecl, TypeDef, TypeExpr, TypeExprKind, UnaryOp, VariantPatternFields,
+    params_have_self,
+};
 use crate::resolve::ResolvedImports;
 use crate::stdlib::StdlibRegistry;
 use crate::type_layout;
@@ -309,6 +316,7 @@ impl Default for Checker {
 }
 
 impl Checker {
+    #[allow(clippy::too_many_lines)]
     pub fn new() -> Self {
         let mut env = TypeEnv::new();
 
@@ -685,6 +693,8 @@ impl Checker {
     /// that need additional state off the checker (references, traits,
     /// etc.) can read it afterward.
     #[allow(clippy::type_complexity)]
+    #[allow(clippy::too_many_lines)]
+    #[allow(clippy::cognitive_complexity)]
     pub(crate) fn check_all(
         &mut self,
         program: &Program,
@@ -762,7 +772,7 @@ impl Checker {
                 self.env.define(&func.name, fn_type);
                 self.unused
                     .defined_sources
-                    .insert(func.name.clone(), format!("function from \"{}\"", source));
+                    .insert(func.name.clone(), format!("function from \"{source}\""));
                 if required_params < func.params.len() {
                     self.fn_required_params
                         .insert(func.name.clone(), required_params);

crates/floe-core/src/checker/attach.rs

@@ -12,7 +12,13 @@
 use std::collections::{HashMap, HashSet};
 use std::sync::{Arc, LazyLock};
 
-use crate::parser::ast::*;
+use crate::parser::ast::{
+    Arg, ConstDecl, Expr, ExprId, ExprKind, FnTypeParam, ForBlock, FunctionDecl, Item, ItemKind,
+    JsxChild, JsxElement, JsxElementKind, JsxProp, MatchArm, Param, Program, RecordEntry,
+    RecordField, RecordSpread, TemplatePart, TestBlock, TestStatement, TraitDecl, TraitMethod,
+    TypeDecl, TypeDef, TypeExpr, TypeExprKind, TypedExpr, TypedProgram, TypedTraitDecl,
+    TypedTypeDecl, UntypedExpr, UntypedProgram, Variant, VariantField,
+};
 use crate::resolve::ResolvedImports;
 
 use super::{ExprTypeMap, Type, UNKNOWN};
@@ -390,6 +396,7 @@ impl Attacher<'_> {
         Box::new(self.expr(*expr))
     }
 
+    #[allow(clippy::too_many_lines)]
     fn expr_kind(&self, kind: ExprKind<()>) -> ExprKind<Arc<Type>> {
         match kind {
             ExprKind::Number(n) => ExprKind::Number(n),

crates/floe-core/src/checker/environment.rs

@@ -152,7 +152,6 @@ impl TypeEnv {
                     ty.clone()
                 }
             }
-            Type::Promise(_) => ty.clone(),
             _ => ty.clone(),
         }
     }