New upstream version 1.52.1+dfsg1

[rustc.git] / src / tools / clippy / clippy_lints / src / mem_discriminant.rs

diff --git a/src/tools/clippy/clippy_lints/src/mem_discriminant.rs b/src/tools/clippy/clippy_lints/src/mem_discriminant.rs
new file mode 100644 (file)
index 0000000..c71c2ee
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/mem_discriminant.rs
@@ -0,0 +1,81 @@
+use crate::utils::{match_def_path, paths, snippet, span_lint_and_then, walk_ptrs_ty_depth};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{BorrowKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+use std::iter;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for calls of `mem::discriminant()` on a non-enum type.
+    ///
+    /// **Why is this bad?** The value of `mem::discriminant()` on non-enum types
+    /// is unspecified.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// use std::mem;
+    ///
+    /// mem::discriminant(&"hello");
+    /// mem::discriminant(&&Some(2));
+    /// ```
+    pub MEM_DISCRIMINANT_NON_ENUM,
+    correctness,
+    "calling `mem::descriminant` on non-enum type"
+}
+
+declare_lint_pass!(MemDiscriminant => [MEM_DISCRIMINANT_NON_ENUM]);
+
+impl<'tcx> LateLintPass<'tcx> for MemDiscriminant {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if_chain! {
+            if let ExprKind::Call(ref func, ref func_args) = expr.kind;
+            // is `mem::discriminant`
+            if let ExprKind::Path(ref func_qpath) = func.kind;
+            if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
+            if match_def_path(cx, def_id, &paths::MEM_DISCRIMINANT);
+            // type is non-enum
+            let ty_param = cx.typeck_results().node_substs(func.hir_id).type_at(0);
+            if !ty_param.is_enum();
+
+            then {
+                span_lint_and_then(
+                    cx,
+                    MEM_DISCRIMINANT_NON_ENUM,
+                    expr.span,
+                    &format!("calling `mem::discriminant` on non-enum type `{}`", ty_param),
+                    |diag| {
+                        // if this is a reference to an enum, suggest dereferencing
+                        let (base_ty, ptr_depth) = walk_ptrs_ty_depth(ty_param);
+                        if ptr_depth >= 1 && base_ty.is_enum() {
+                            let param = &func_args[0];
+
+                            // cancel out '&'s first
+                            let mut derefs_needed = ptr_depth;
+                            let mut cur_expr = param;
+                            while derefs_needed > 0  {
+                                if let ExprKind::AddrOf(BorrowKind::Ref, _, ref inner_expr) = cur_expr.kind {
+                                    derefs_needed -= 1;
+                                    cur_expr = inner_expr;
+                                } else {
+                                    break;
+                                }
+                            }
+
+                            let derefs: String = iter::repeat('*').take(derefs_needed).collect();
+                            diag.span_suggestion(
+                                param.span,
+                                "try dereferencing",
+                                format!("{}{}", derefs, snippet(cx, cur_expr.span, "<param>")),
+                                Applicability::MachineApplicable,
+                            );
+                        }
+                    },
+                )
+            }
+        }
+    }
+}