Update upstream source from tag 'upstream/1.52.1+dfsg1'

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

diff --git a/src/tools/clippy/clippy_lints/src/manual_unwrap_or.rs b/src/tools/clippy/clippy_lints/src/manual_unwrap_or.rs
new file mode 100644 (file)
index 0000000..b452225
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/manual_unwrap_or.rs
@@ -0,0 +1,127 @@
+use crate::consts::constant_simple;
+use crate::utils;
+use crate::utils::{path_to_local_id, sugg};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{Arm, Expr, ExprKind, Pat, PatKind};
+use rustc_lint::LintContext;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::lint::in_external_macro;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// **What it does:**
+    /// Finds patterns that reimplement `Option::unwrap_or` or `Result::unwrap_or`.
+    ///
+    /// **Why is this bad?**
+    /// Concise code helps focusing on behavior instead of boilerplate.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let foo: Option<i32> = None;
+    /// match foo {
+    ///     Some(v) => v,
+    ///     None => 1,
+    /// };
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// let foo: Option<i32> = None;
+    /// foo.unwrap_or(1);
+    /// ```
+    pub MANUAL_UNWRAP_OR,
+    complexity,
+    "finds patterns that can be encoded more concisely with `Option::unwrap_or` or `Result::unwrap_or`"
+}
+
+declare_lint_pass!(ManualUnwrapOr => [MANUAL_UNWRAP_OR]);
+
+impl LateLintPass<'_> for ManualUnwrapOr {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if in_external_macro(cx.sess(), expr.span) {
+            return;
+        }
+        lint_manual_unwrap_or(cx, expr);
+    }
+}
+
+#[derive(Copy, Clone)]
+enum Case {
+    Option,
+    Result,
+}
+
+impl Case {
+    fn unwrap_fn_path(&self) -> &str {
+        match self {
+            Case::Option => "Option::unwrap_or",
+            Case::Result => "Result::unwrap_or",
+        }
+    }
+}
+
+fn lint_manual_unwrap_or<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+    fn applicable_or_arm<'a>(arms: &'a [Arm<'a>]) -> Option<&'a Arm<'a>> {
+        if_chain! {
+            if arms.len() == 2;
+            if arms.iter().all(|arm| arm.guard.is_none());
+            if let Some((idx, or_arm)) = arms.iter().enumerate().find(|(_, arm)|
+                match arm.pat.kind {
+                    PatKind::Path(ref some_qpath) =>
+                        utils::match_qpath(some_qpath, &utils::paths::OPTION_NONE),
+                    PatKind::TupleStruct(ref err_qpath, &[Pat { kind: PatKind::Wild, .. }], _) =>
+                        utils::match_qpath(err_qpath, &utils::paths::RESULT_ERR),
+                    _ => false,
+                }
+            );
+            let unwrap_arm = &arms[1 - idx];
+            if let PatKind::TupleStruct(ref unwrap_qpath, &[unwrap_pat], _) = unwrap_arm.pat.kind;
+            if utils::match_qpath(unwrap_qpath, &utils::paths::OPTION_SOME)
+                || utils::match_qpath(unwrap_qpath, &utils::paths::RESULT_OK);
+            if let PatKind::Binding(_, binding_hir_id, ..) = unwrap_pat.kind;
+            if path_to_local_id(unwrap_arm.body, binding_hir_id);
+            if !utils::usage::contains_return_break_continue_macro(or_arm.body);
+            then {
+                Some(or_arm)
+            } else {
+                None
+            }
+        }
+    }
+
+    if_chain! {
+        if let ExprKind::Match(scrutinee, match_arms, _) = expr.kind;
+        let ty = cx.typeck_results().expr_ty(scrutinee);
+        if let Some(case) = if utils::is_type_diagnostic_item(cx, ty, sym::option_type) {
+            Some(Case::Option)
+        } else if utils::is_type_diagnostic_item(cx, ty, sym::result_type) {
+            Some(Case::Result)
+        } else {
+            None
+        };
+        if let Some(or_arm) = applicable_or_arm(match_arms);
+        if let Some(or_body_snippet) = utils::snippet_opt(cx, or_arm.body.span);
+        if let Some(indent) = utils::indent_of(cx, expr.span);
+        if constant_simple(cx, cx.typeck_results(), or_arm.body).is_some();
+        then {
+            let reindented_or_body =
+                utils::reindent_multiline(or_body_snippet.into(), true, Some(indent));
+            utils::span_lint_and_sugg(
+                cx,
+                MANUAL_UNWRAP_OR, expr.span,
+                &format!("this pattern reimplements `{}`", case.unwrap_fn_path()),
+                "replace with",
+                format!(
+                    "{}.unwrap_or({})",
+                    sugg::Sugg::hir(cx, scrutinee, "..").maybe_par(),
+                    reindented_or_body,
+                ),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}