feat(jans-cedarling): add custom linter for inefficient string concatenation

.github/workflows/test-cedarling.yml

@@ -29,6 +29,32 @@ jobs:
       run: |
         rustup component add clippy
         cargo clippy --workspace --all-targets -- -D warnings
+  custom_lints:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Harden Runner
+      uses: step-security/harden-runner@a4aa98b93cab29d9b1101a6143fb8bce00e2eac4 # v2.7.1
+      with:
+        egress-policy: audit
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+    - name: Install Rust Nightly
+      uses: dtolnay/rust-toolchain@1ff72ee08e3cb84d84adba594e0a297990fc1ed3
+      with:
+        toolchain: nightly-2025-09-18
+        components: llvm-tools-preview, rustc-dev
+    - name: Install dylint
+      run: |
+        cargo install cargo-dylint --version 5.0.0 --locked
+        cargo install dylint-link --version 5.0.0 --locked
+    - name: Run Tests
+      working-directory: jans-cedarling/custom-lints
+      run: cargo test
+    - name: Install Rust Stable (for workspace)
+      uses: dtolnay/rust-toolchain@1ff72ee08e3cb84d84adba594e0a297990fc1ed3 # stable
+    - name: Run custom lints on workspace
+      working-directory: jans-cedarling
+      run: |
+        RUSTFLAGS="-Dwarnings" cargo dylint --all --workspace --path custom-lints
   rust_benchmarks:
     runs-on: ubuntu-latest
     steps:

jans-cedarling/Cargo.toml

@@ -1,7 +1,7 @@
 [workspace]
 resolver = "2"
 members = ["bindings/*", "cedarling", "http_utils", "sparkv", "test_utils"]
-exclude = ["bindings/cedarling-java"]
+exclude = ["bindings/cedarling-java", "custom-lints"]
 
 [workspace.dependencies]
 serde = { version = "1.0", features = ["derive"] }

jans-cedarling/custom-lints/.cargo/config.toml

@@ -0,0 +1,6 @@
+[target.'cfg(all())']
+rustflags = ["-C", "linker=dylint-link"]
+
+# For Rust versions 1.74.0 and onward, the following alternative can be used
+# (see https://github.com/rust-lang/cargo/pull/12535):
+# linker = "dylint-link"

jans-cedarling/custom-lints/.gitignore

@@ -0,0 +1 @@
+/target

jans-cedarling/custom-lints/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "custom_lints"
+version = "0.1.0"
+description = "Custom lints for the Cedarling"
+edition = "2024"
+publish = false
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+clippy_utils = { git = "https://github.com/rust-lang/rust-clippy", rev = "20ce69b9a63bcd2756cd906fe0964d1e901e042a" }
+dylint_linting = "5.0.0"
+
+[dev-dependencies]
+dylint_testing = "5.0.0"
+
+[package.metadata.rust-analyzer]
+rustc_private = true

jans-cedarling/custom-lints/rust-toolchain

@@ -0,0 +1,3 @@
+[toolchain]
+channel = "nightly-2025-09-18"
+components = ["llvm-tools-preview", "rustc-dev"]

jans-cedarling/custom-lints/src/lib.rs

@@ -0,0 +1,149 @@
+// This software is available under the Apache-2.0 license.
+// See https://www.apache.org/licenses/LICENSE-2.0.txt for full text.
+//
+// Copyright (c) 2024, Gluu, Inc.
+
+#![feature(rustc_private)]
+#![warn(unused_extern_crates)]
+
+extern crate rustc_ast;
+extern crate rustc_errors;
+extern crate rustc_hir;
+extern crate rustc_span;
+
+use clippy_utils::{
+    diagnostics::{span_lint_and_help, span_lint_and_sugg},
+    source::snippet,
+    sym,
+};
+use rustc_ast::LitKind::Str;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, QPath, TyKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_span::{Symbol, source_map::Spanned};
+
+dylint_linting::declare_late_lint! {
+    /// ### What it does
+    /// Checks for `EntityUid::from_str(&format!(...))` pattern which is explicitly
+    /// warned against in the Cedar documentation for performance reasons.
+    ///
+    /// ### Why is this bad?
+    /// The Cedar crate documentation specifically warns that using `format!()`
+    /// with `EntityUid::from_str` is inefficient. Use string literals instead.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// EntityUid::from_str(&format!("{}::\"{}\"", entity_type, id))
+    /// ```
+    ///
+    /// Use instead:
+    ///
+    /// ```rust
+    /// let entity_type_name = EntityTypeName::from_str(entity_type).unwrap();
+    /// let entity_id = EntityId::from_str(id).unwrap_or_else(|e| match e {});
+    ///
+    /// EntityUid::from_type_name_and_id(entity_type_name, entity_id)
+    /// ```
+    pub BAD_STRING_CONCATENATION,
+    Warn,
+    "using EntityUid::from_str with format!() is inefficient"
+}
+
+impl<'tcx> LateLintPass<'tcx> for BadStringConcatenation {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        // This checks if the expression kind is a function call extracting
+        // the function itself and its arguments
+        if let ExprKind::Call(callee, [arg]) = &expr.kind
+            // Checks the function's kind is a path to definition e.g., Vec::new or EntityUid::from_str
+            && let ExprKind::Path(QPath::TypeRelative(ty, segment)) = &callee.kind
+            // Checks the function's type is a path to a type e.g., Vec<T> or EntityUid
+            && let TyKind::Path(QPath::Resolved(_, path)) = &ty.kind
+            // Checks for the type path segments identifier is `EntityUid` or not
+            // e.g., cedar_policy::EntityUid::from_str will have 2 path segments cedar_policy and EntityUid
+            && path.segments.last().is_some_and(|s| s.ident.name.as_str().eq("EntityUid"))
+            // Checks if the function name is `from_str` or not
+            && segment.ident.name == sym::from_str
+            // Checks if the argument of `from_str` is a reference and extract the expression inside
+            && let ExprKind::AddrOf(_, _, exp) = arg.kind
+            // Checks if the argument inside `from_str` is a function call then extract the
+            // argument of said function
+            && let ExprKind::Call(_, [format_call]) = exp.kind
+            && let ExprKind::Block(block, _) = format_call.kind
+            && is_format_macro(cx, block.expr)
+            && let Some(bexpr) = block.expr
+            && let ExprKind::Call(_, [format_arg]) = &bexpr.kind
+        {
+            if let Some(arg) = extract_string_literal(format_arg) {
+                let ty_snippet = snippet(cx, ty.span, "EntityUid");
+                span_lint_and_sugg(
+                    cx,
+                    BAD_STRING_CONCATENATION,
+                    expr.span,
+                    "using `EntityUid::from_str` with format! is inefficient",
+                    "try this instead",
+                    format!("{ty_snippet}::from_str({arg:?})"),
+                    Applicability::MachineApplicable,
+                );
+            } else {
+                span_lint_and_help(
+                    cx,
+                    BAD_STRING_CONCATENATION,
+                    expr.span,
+                    "using `EntityUid::from_str` with format! is inefficient",
+                    None,
+                    "consider using `EntityUid::from_type_name_and_id` instead",
+                );
+            }
+        }
+    }
+}
+
+/// Checks if the given expression is a format macro or not
+fn is_format_macro<'tcx>(cx: &LateContext<'tcx>, expr: Option<&Expr<'tcx>>) -> bool {
+    if let Some(expr) = expr
+        && let ExprKind::Call(callee, _) = &expr.kind
+        && let ExprKind::Path(QPath::Resolved(_, path)) = &callee.kind
+    {
+        if path.segments.len() >= 2 {
+            let last_two: Vec<_> = path
+                .segments
+                .iter()
+                .rev()
+                .take(2)
+                .map(|s| s.ident.name.as_str())
+                .collect();
+
+            if last_two[0] == "format" && last_two[1] == "fmt" {
+                return true;
+            }
+        }
+
+        // Fallback: check def_id
+        if let Some(def_id) = path.res.opt_def_id() {
+            let path_str = cx.tcx.def_path_str(def_id);
+            return matches!(path_str.as_str(), "alloc::fmt::format" | "std::fmt::format");
+        }
+    }
+    false
+}
+
+// Checks if the argument of format macro is a string literal and extract it
+fn extract_string_literal(expr: &Expr<'_>) -> Option<Symbol> {
+    if let ExprKind::Call(_, [arg]) = expr.kind
+        && let ExprKind::AddrOf(_, _, expr) = arg.kind
+        && let ExprKind::Array([element]) = expr.kind
+        && let ExprKind::Lit(Spanned {
+            node: Str(item, _), ..
+        }) = element.kind
+    {
+        return Some(item);
+    }
+
+    None
+}
+
+#[test]
+fn ui() {
+    dylint_testing::ui_test(env!("CARGO_PKG_NAME"), "ui");
+}

jans-cedarling/custom-lints/ui/main.rs

@@ -0,0 +1,39 @@
+#![allow(unused)]
+
+use cedar_policy::EntityUid;
+
+fn main() {
+    // This should trigger the lint
+    let eid1 = EntityUid::from_str(&format!(r#"User::"alice""#));
+
+    // This should trigger the lint
+    let user = "alice";
+    let eid2 = EntityUid::from_str(&format!(r#"User::"{}""#, user));
+
+    // This should trigger the lint - (even with std::format!)
+    let eid3 = EntityUid::from_str(&std::format!(r#"User::"bob""#));
+
+    // This should NOT trigger
+    let eid4 = EntityUid::from_str(r#"User::"alice""#);
+
+    // This should NOT trigger
+    let literal = String::from(r#"User::"dave""#);
+    let eid5 = EntityUid::from_str(&literal);
+
+    let entity_type_name = "Jans::User";
+    let entity_id = "user123";
+    let eid7 = cedar_policy::EntityUid::from_str(&format!(r#"{entity_type_name}::"{entity_id}""#));
+
+    let eid8 = cedar_policy::EntityUid::from_str(&format!(r#"Jans::User::"bob123""#));
+}
+
+// Mock EntityUid for testing (since we don't want to pull in the actual Cedar crate)
+mod cedar_policy {
+    pub(super) struct EntityUid;
+
+    impl EntityUid {
+        pub(super) fn from_str(s: &str) -> Result<Self, String> {
+            Ok(EntityUid)
+        }
+    }
+}

jans-cedarling/custom-lints/ui/main.stderr

@@ -0,0 +1,38 @@
+warning: using `EntityUid::from_str` with format! is inefficient
+  --> $DIR/main.rs:7:16
+   |
+LL |     let eid1 = EntityUid::from_str(&format!(r#"User::"alice""#));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this instead: `EntityUid::from_str("User::/"alice/"")`
+   |
+   = note: `#[warn(bad_string_concatenation)]` on by default
+
+warning: using `EntityUid::from_str` with format! is inefficient
+  --> $DIR/main.rs:11:16
+   |
+LL |     let eid2 = EntityUid::from_str(&format!(r#"User::"{}""#, user));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider using `EntityUid::from_type_name_and_id` instead
+
+warning: using `EntityUid::from_str` with format! is inefficient
+  --> $DIR/main.rs:14:16
+   |
+LL |     let eid3 = EntityUid::from_str(&std::format!(r#"User::"bob""#));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this instead: `EntityUid::from_str("User::/"bob/"")`
+
+warning: using `EntityUid::from_str` with format! is inefficient
+  --> $DIR/main.rs:25:16
+   |
+LL |     let eid7 = cedar_policy::EntityUid::from_str(&format!(r#"{entity_type_name}::"{entity_id}""#));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider using `EntityUid::from_type_name_and_id` instead
+
+warning: using `EntityUid::from_str` with format! is inefficient
+  --> $DIR/main.rs:27:16
+   |
+LL |     let eid8 = cedar_policy::EntityUid::from_str(&format!(r#"Jans::User::"bob123""#));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this instead: `cedar_policy::EntityUid::from_str("Jans::User::/"bob123/"")`
+
+warning: 5 warnings emitted
+