Add #[clippy::print_hir] attribute for debugging

Author: xFrednet

clippy_lints/src/lib.rs

@@ -514,6 +514,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     }
 
     store.register_late_pass(|| Box::new(utils::author::Author));
+    store.register_late_pass(|| Box::new(utils::print_hir::PrintHir));
     store.register_late_pass(|| Box::new(await_holding_invalid::AwaitHolding));
     store.register_late_pass(|| Box::new(serde_api::SerdeApi));
     let vec_box_size_threshold = conf.vec_box_size_threshold;

clippy_lints/src/utils/internal_lints/metadata_collector.rs

@@ -33,7 +33,12 @@ use std::path::Path;
 /// This is the output file of the lint collector.
 const OUTPUT_FILE: &str = "../util/gh-pages/lints.json";
 /// These lints are excluded from the export.
-const BLACK_LISTED_LINTS: [&str; 3] = ["lint_author", "deep_code_inspection", "internal_metadata_collector"];
+const BLACK_LISTED_LINTS: &[&str] = &[
+    "lint_author",
+    "deep_code_inspection",
+    "internal_metadata_collector",
+    "print_ast",
+];
 /// These groups will be ignored by the lint group matcher. This is useful for collections like
 /// `clippy::all`
 const IGNORED_LINT_GROUPS: [&str; 1] = ["clippy::all"];

clippy_lints/src/utils/mod.rs

@@ -3,3 +3,4 @@ pub mod conf;
 pub mod inspector;
 #[cfg(feature = "internal")]
 pub mod internal_lints;
+pub mod print_hir;

clippy_lints/src/utils/print_hir.rs

@@ -0,0 +1,45 @@
+use clippy_utils::get_attr;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// It formats the attached node with `{:#?}` and writes the result to the
+    /// standard output. This is intended for debugging.
+    ///
+    pub PRINT_HIR,
+    internal_warn,
+    "helper for writing lints"
+}
+
+declare_lint_pass!(PrintHir => [PRINT_HIR]);
+
+impl<'tcx> LateLintPass<'tcx> for PrintHir {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
+        if has_attr(cx, item.hir_id()) {
+            println!("{item:#?}");
+        }
+    }
+
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
+        if has_attr(cx, expr.hir_id) {
+            println!("{expr:#?}");
+        }
+    }
+
+    fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx hir::Stmt<'_>) {
+        match stmt.kind {
+            hir::StmtKind::Expr(e) | hir::StmtKind::Semi(e) if has_attr(cx, e.hir_id) => return,
+            _ => {},
+        }
+        if has_attr(cx, stmt.hir_id) {
+            println!("{stmt:#?}");
+        }
+    }
+}
+
+fn has_attr(cx: &LateContext<'_>, hir_id: hir::HirId) -> bool {
+    let attrs = cx.tcx.hir().attrs(hir_id);
+    get_attr(cx.sess(), attrs, "print_hir").count() > 0
+}

clippy_utils/src/attrs.rs

@@ -17,6 +17,7 @@ pub enum DeprecationStatus {
 #[rustfmt::skip]
 pub const BUILTIN_ATTRIBUTES: &[(&str, DeprecationStatus)] = &[
     ("author",                DeprecationStatus::None),
+    ("print_hir",             DeprecationStatus::None),
     ("version",               DeprecationStatus::None),
     ("cognitive_complexity",  DeprecationStatus::None),
     ("cyclomatic_complexity", DeprecationStatus::Replaced("cognitive_complexity")),

doc/adding_lints.md

@@ -22,6 +22,7 @@ because that's clearly a non-descriptive name.
   - [Adding the lint logic](#adding-the-lint-logic)
   - [Specifying the lint's minimum supported Rust version (MSRV)](#specifying-the-lints-minimum-supported-rust-version-msrv)
   - [Author lint](#author-lint)
+  - [Print HIR lint](#print-hir-lint)
   - [Documentation](#documentation)
   - [Running rustfmt](#running-rustfmt)
   - [Debugging](#debugging)
@@ -484,6 +485,19 @@ you are implementing your lint.
 
 [author_example]: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=9a12cb60e5c6ad4e3003ac6d5e63cf55
 
+## Print HIR lint
+
+To implement a lint, it's helpful to first understand the internal representation
+that rustc uses. Clippy has the `#[clippy::print_hir]` attribute that prints the
+[`High-Level Intermediate Representation (HIR)`] of the item, statement, or 
+expression that the attribute is attached to. To attach the attribute to expressions
+you often need to enable `#![feature(stmt_expr_attributes)]`.
+
+[Here][print_hir_example] you can find an example, just select _Tools_ and run _Clippy_.
+
+[`High-Level Intermediate Representation (HIR)`]: https://rustc-dev-guide.rust-lang.org/hir.html
+[print_hir_example]: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=54d0f768e0ad9f333872f01c2c701bd5
+
 ## Documentation
 
 The final thing before submitting our PR is to add some documentation to our