Add OUTER_EXPN_INFO lint

Author: Michael Wright

clippy_lints/src/lib.rs

@@ -429,6 +429,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     reg.register_early_lint_pass(box utils::internal_lints::ClippyLintsInternal);
     reg.register_late_lint_pass(box utils::internal_lints::CompilerLintFunctions::new());
     reg.register_late_lint_pass(box utils::internal_lints::LintWithoutLintPass::default());
+    reg.register_late_lint_pass(box utils::internal_lints::OuterExpnInfoPass);
     reg.register_late_lint_pass(box utils::inspector::DeepCodeInspector);
     reg.register_late_lint_pass(box utils::author::Author);
     reg.register_late_lint_pass(box types::Types);
@@ -659,6 +660,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
         utils::internal_lints::CLIPPY_LINTS_INTERNAL,
         utils::internal_lints::COMPILER_LINT_FUNCTIONS,
         utils::internal_lints::LINT_WITHOUT_LINT_PASS,
+        utils::internal_lints::OUTER_EXPN_INFO,
     ]);
 
     reg.register_lint_group("clippy::all", Some("clippy"), vec![

clippy_lints/src/utils/internal_lints.rs

@@ -1,4 +1,6 @@
-use crate::utils::{match_def_path, match_type, paths, span_help_and_lint, span_lint, walk_ptrs_ty};
+use crate::utils::{
+    match_def_path, match_type, method_calls, paths, span_help_and_lint, span_lint, span_lint_and_sugg, walk_ptrs_ty,
+};
 use if_chain::if_chain;
 use rustc::hir;
 use rustc::hir::def::{DefKind, Res};
@@ -7,6 +9,7 @@ use rustc::hir::*;
 use rustc::lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintArray, LintPass};
 use rustc::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::Applicability;
 use syntax::ast::{Crate as AstCrate, ItemKind, Name};
 use syntax::source_map::Span;
 use syntax_pos::symbol::LocalInternedString;
@@ -72,6 +75,29 @@ declare_clippy_lint! {
     "usage of the lint functions of the compiler instead of the utils::* variant"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for calls to `cx.outer().expn_info()` and suggests to use
+    /// the `cx.outer_expn_info()`
+    ///
+    /// **Why is this bad?** `cx.outer_expn_info()` is faster and more concise.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// Bad:
+    /// ```rust
+    /// expr.span.ctxt().outer().expn_info()
+    /// ```
+    ///
+    /// Good:
+    /// ```rust
+    /// expr.span.ctxt().outer_expn_info()
+    /// ```
+    pub OUTER_EXPN_INFO,
+    internal,
+    "using `cx.outer().expn_info()` instead of `cx.outer_expn_info()`"
+}
+
 declare_lint_pass!(ClippyLintsInternal => [CLIPPY_LINTS_INTERNAL]);
 
 impl EarlyLintPass for ClippyLintsInternal {
@@ -251,3 +277,34 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CompilerLintFunctions {
         }
     }
 }
+
+pub struct OuterExpnInfoPass;
+
+impl_lint_pass!(OuterExpnInfoPass => [OUTER_EXPN_INFO]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for OuterExpnInfoPass {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
+        let (method_names, arg_lists) = method_calls(expr, 2);
+        let method_names: Vec<LocalInternedString> = method_names.iter().map(|s| s.as_str()).collect();
+        let method_names: Vec<&str> = method_names.iter().map(std::convert::AsRef::as_ref).collect();
+        if_chain! {
+            if let ["expn_info", "outer"] = method_names.as_slice();
+            let args = arg_lists[1];
+            if args.len() == 1;
+            let self_arg = &args[0];
+            let self_ty = walk_ptrs_ty(cx.tables.expr_ty(self_arg));
+            if match_type(cx, self_ty, &paths::SYNTAX_CONTEXT);
+            then {
+                span_lint_and_sugg(
+                    cx,
+                    OUTER_EXPN_INFO,
+                    expr.span.trim_start(self_arg.span).unwrap_or(expr.span),
+                    "usage of `outer().expn_info()`",
+                    "try",
+                    ".outer_expn_info()".to_string(),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+    }
+}

clippy_lints/src/utils/paths.rs

@@ -101,6 +101,7 @@ pub const STDOUT: [&str; 4] = ["std", "io", "stdio", "stdout"];
 pub const STD_MEM_TRANSMUTE: [&str; 3] = ["std", "mem", "transmute"];
 pub const STD_PTR_NULL: [&str; 3] = ["std", "ptr", "null"];
 pub const STRING: [&str; 3] = ["alloc", "string", "String"];
+pub const SYNTAX_CONTEXT: [&str; 3] = ["syntax_pos", "hygiene", "SyntaxContext"];
 pub const TO_OWNED: [&str; 3] = ["alloc", "borrow", "ToOwned"];
 pub const TO_OWNED_METHOD: [&str; 4] = ["alloc", "borrow", "ToOwned", "to_owned"];
 pub const TO_STRING: [&str; 3] = ["alloc", "string", "ToString"];

tests/ui/outer_expn_info.rs

@@ -0,0 +1,23 @@
+#![deny(clippy::internal)]
+#![feature(rustc_private)]
+
+#[macro_use]
+extern crate rustc;
+use rustc::hir::Expr;
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+
+declare_lint! {
+    pub TEST_LINT,
+    Warn,
+    ""
+}
+
+declare_lint_pass!(Pass => [TEST_LINT]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
+    fn check_expr(&mut self, _cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
+        let _ = expr.span.ctxt().outer().expn_info();
+    }
+}
+
+fn main() {}

tests/ui/outer_expn_info.stderr

@@ -0,0 +1,15 @@
+error: usage of `outer().expn_info()`
+  --> $DIR/outer_expn_info.rs:19:33
+   |
+LL |         let _ = expr.span.ctxt().outer().expn_info();
+   |                                 ^^^^^^^^^^^^^^^^^^^^ help: try: `.outer_expn_info()`
+   |
+note: lint level defined here
+  --> $DIR/outer_expn_info.rs:1:9
+   |
+LL | #![deny(clippy::internal)]
+   |         ^^^^^^^^^^^^^^^^
+   = note: #[deny(clippy::outer_expn_info)] implied by #[deny(clippy::internal)]
+
+error: aborting due to previous error
+