Move expression check to LateLintPass

Changes:
- Move from EarlyLintPass
- Fix entrypoint check with function path def_id.

clippy_lints/src/lib.rs

@@ -469,7 +469,8 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     reg.register_late_lint_pass(box types::LetUnitValue);
     reg.register_late_lint_pass(box types::UnitCmp);
     reg.register_late_lint_pass(box loops::Loops);
-    reg.register_early_lint_pass(box main_recursion::MainRecursion::new());
+    // reg.register_early_lint_pass(box main_recursion::MainRecursion::new());
+    reg.register_late_lint_pass(box main_recursion::MainRecursion::new());
     reg.register_late_lint_pass(box lifetimes::Lifetimes);
     reg.register_late_lint_pass(box entry::HashMapPass);
     reg.register_late_lint_pass(box ranges::Ranges);
@@ -916,6 +917,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         let_if_seq::USELESS_LET_IF_SEQ,
         literal_representation::INCONSISTENT_DIGIT_GROUPING,
         literal_representation::UNREADABLE_LITERAL,
+        main_recursion::MAIN_RECURSION,
         loops::EMPTY_LOOP,
         loops::FOR_KV_MAP,
         loops::NEEDLESS_RANGE_LOOP,

clippy_lints/src/main_recursion.rs

@@ -1,16 +1,30 @@
 
-use syntax::ast::{Crate, Expr, ExprKind};
 use syntax::symbol::sym;
-use rustc::lint::{LintArray, LintPass, EarlyLintPass, EarlyContext};
+use rustc::lint::{LintArray, LintPass, LateLintPass, LateContext};
+use rustc::hir::{Crate, Expr, ExprKind, QPath};
+use rustc::hir::def::Res;
 use rustc::{declare_tool_lint, impl_lint_pass};
 
 use if_chain::if_chain;
-use crate::utils::span_help_and_lint;
+use crate::utils::{span_help_and_lint, is_entrypoint_fn};
 
 declare_clippy_lint! {
+    /// **What it does:** Checks for recursion using the entrypoint.
+    ///
+    /// **Why is this bad?** Apart from special setups (which we could detect following attributes like #![no_std]),
+    /// recursing into main() seems like an unintuitive antipattern we should be able to detect.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```no_run
+    /// fn main() {
+    ///     main();
+    /// }
+    /// ```
     pub MAIN_RECURSION,
-    pedantic,
-    "function named `foo`, which is not a descriptive name"
+    style,
+    "recursion using the entrypoint"
 }
 
 pub struct MainRecursion {
@@ -27,27 +41,29 @@ impl MainRecursion {
     }
 }
 
-impl EarlyLintPass for MainRecursion {
-    fn check_crate(&mut self, _: &EarlyContext<'_>, krate: &Crate) {
+impl LateLintPass<'_, '_> for MainRecursion {
+    fn check_crate(&mut self, _: &LateContext<'_, '_>, krate: &Crate) {
         self.has_no_std_attr = krate.attrs.iter().any(|attr| attr.path == sym::no_std);
     }
 
-    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
+    fn check_expr_post(&mut self, cx: &LateContext<'_, '_>, expr: &Expr) {
         if self.has_no_std_attr {
             return;
         }
 
         if_chain! {
             if let ExprKind::Call(func, _) = &expr.node;
-            if let ExprKind::Path(_, path) = &func.node;
-            if *path == sym::main;
+            if let ExprKind::Path(path) = &func.node;
+            if let QPath::Resolved(_, ptr) = &path;
+            if let Res::Def(_, def_id) = &ptr.res;
+            if is_entrypoint_fn(cx, *def_id);
             then {
                 span_help_and_lint(
                     cx,
                     MAIN_RECURSION,
-                    expr.span,
-                    "You are recursing into main()",
-                    "Consider using another function for this recursion"
+                    func.span,
+                    "recursing into `main()`",
+                    "consider using another function for this recursion"
                 )
             }
         }

tests/ui/crate_level_checks/entrypoint_recursion.rs

@@ -0,0 +1,9 @@
+#![feature(main)]
+
+#[warn(clippy::main_recursion)]
+#[allow(unconditional_recursion)]
+#[main]
+fn a() {
+    println!("Hello, World!");
+    a();
+}

tests/ui/crate_level_checks/entrypoint_recursion.stderr

@@ -0,0 +1,11 @@
+error: recursing into `main()`
+  --> $DIR/entrypoint_recursion.rs:8:5
+   |
+LL |     a();
+   |     ^
+   |
+   = note: `-D clippy::main-recursion` implied by `-D warnings`
+   = help: consider using another function for this recursion
+
+error: aborting due to previous error
+

tests/ui/crate_level_checks/std_main_recursion.rs

@@ -1,5 +1,6 @@
 #[warn(clippy::main_recursion)]
 #[allow(unconditional_recursion)]
 fn main() {
+    println!("Hello, World!");
     main();
 }

tests/ui/crate_level_checks/std_main_recursion.stderr

@@ -1,11 +1,11 @@
-error: You are recursing into main()
-  --> $DIR/std_main_recursion.rs:4:5
+error: recursing into `main()`
+  --> $DIR/std_main_recursion.rs:5:5
    |
 LL |     main();
-   |     ^^^^^^
+   |     ^^^^
    |
    = note: `-D clippy::main-recursion` implied by `-D warnings`
-   = help: Consider using another function for this recursion
+   = help: consider using another function for this recursion
 
 error: aborting due to previous error