New upstream version 1.52.1+dfsg1

[rustc.git] / src / tools / clippy / clippy_lints / src / methods / ok_expect.rs

diff --git a/src/tools/clippy/clippy_lints/src/methods/ok_expect.rs b/src/tools/clippy/clippy_lints/src/methods/ok_expect.rs
new file mode 100644 (file)
index 0000000..c1706cc
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/ok_expect.rs
@@ -0,0 +1,45 @@
+use crate::utils::{implements_trait, is_type_diagnostic_item, span_lint_and_help};
+use if_chain::if_chain;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::sym;
+
+use super::OK_EXPECT;
+
+/// lint use of `ok().expect()` for `Result`s
+pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ok_args: &[hir::Expr<'_>]) {
+    if_chain! {
+        // lint if the caller of `ok()` is a `Result`
+        if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&ok_args[0]), sym::result_type);
+        let result_type = cx.typeck_results().expr_ty(&ok_args[0]);
+        if let Some(error_type) = get_error_type(cx, result_type);
+        if has_debug_impl(error_type, cx);
+
+        then {
+            span_lint_and_help(
+                cx,
+                OK_EXPECT,
+                expr.span,
+                "called `ok().expect()` on a `Result` value",
+                None,
+                "you can call `expect()` directly on the `Result`",
+            );
+        }
+    }
+}
+
+/// Given a `Result<T, E>` type, return its error type (`E`).
+fn get_error_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option<Ty<'a>> {
+    match ty.kind() {
+        ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym::result_type) => substs.types().nth(1),
+        _ => None,
+    }
+}
+
+/// This checks whether a given type is known to implement Debug.
+fn has_debug_impl<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
+    cx.tcx
+        .get_diagnostic_item(sym::debug_trait)
+        .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
+}