Adjust the output of unnecessary_unwrap and provide a suggestion

Author: shepmaster

clippy_lints/src/unwrap.rs

@@ -1,10 +1,11 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher;
 use clippy_utils::ty::is_type_diagnostic_item;
-use clippy_utils::{differing_macro_contexts, usage::is_potentially_mutated};
+use clippy_utils::{differing_macro_contexts, path_to_local, usage::is_potentially_mutated};
 use if_chain::if_chain;
+use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
-use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, Path, QPath, UnOp};
+use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, PathSegment, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::map::Map;
 use rustc_middle::lint::in_external_macro;
@@ -74,26 +75,61 @@ struct UnwrappableVariablesVisitor<'a, 'tcx> {
     unwrappables: Vec<UnwrapInfo<'tcx>>,
     cx: &'a LateContext<'tcx>,
 }
+
+/// What kind of unwrappable this is.
+#[derive(Copy, Clone, Debug)]
+enum UnwrappableKind {
+    Option,
+    Result,
+}
+
+impl UnwrappableKind {
+    fn success_variant_pattern(self) -> &'static str {
+        match self {
+            UnwrappableKind::Option => "Some(..)",
+            UnwrappableKind::Result => "Ok(..)",
+        }
+    }
+
+    fn error_variant_pattern(self) -> &'static str {
+        match self {
+            UnwrappableKind::Option => "None",
+            UnwrappableKind::Result => "Err(..)",
+        }
+    }
+}
+
 /// Contains information about whether a variable can be unwrapped.
 #[derive(Copy, Clone, Debug)]
 struct UnwrapInfo<'tcx> {
     /// The variable that is checked
-    ident: &'tcx Path<'tcx>,
+    local_id: HirId,
+    /// The if itself
+    if_expr: &'tcx Expr<'tcx>,
     /// The check, like `x.is_ok()`
     check: &'tcx Expr<'tcx>,
+    /// The check's name, like `is_ok`
+    check_name: &'tcx PathSegment<'tcx>,
     /// The branch where the check takes place, like `if x.is_ok() { .. }`
     branch: &'tcx Expr<'tcx>,
     /// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
     safe_to_unwrap: bool,
+    /// What kind of unwrappable this is.
+    kind: UnwrappableKind,
+    /// If the check is the entire condition (`if x.is_ok()`) or only a part of it (`foo() &&
+    /// x.is_ok()`)
+    is_entire_condition: bool,
 }
 
 /// Collects the information about unwrappable variables from an if condition
 /// The `invert` argument tells us whether the condition is negated.
 fn collect_unwrap_info<'tcx>(
     cx: &LateContext<'tcx>,
+    if_expr: &'tcx Expr<'_>,
     expr: &'tcx Expr<'_>,
     branch: &'tcx Expr<'_>,
     invert: bool,
+    is_entire_condition: bool,
 ) -> Vec<UnwrapInfo<'tcx>> {
     fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
         is_type_diagnostic_item(cx, ty, sym::option_type) && ["is_some", "is_none"].contains(&method_name)
@@ -106,18 +142,18 @@ fn collect_unwrap_info<'tcx>(
     if let ExprKind::Binary(op, left, right) = &expr.kind {
         match (invert, op.node) {
             (false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
-                let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
-                unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
+                let mut unwrap_info = collect_unwrap_info(cx, if_expr, left, branch, invert, false);
+                unwrap_info.append(&mut collect_unwrap_info(cx, if_expr, right, branch, invert, false));
                 return unwrap_info;
             },
             _ => (),
         }
     } else if let ExprKind::Unary(UnOp::Not, expr) = &expr.kind {
-        return collect_unwrap_info(cx, expr, branch, !invert);
+        return collect_unwrap_info(cx, if_expr, expr, branch, !invert, false);
     } else {
         if_chain! {
             if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
-            if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
+            if let Some(local_id) = path_to_local(&args[0]);
             let ty = cx.typeck_results().expr_ty(&args[0]);
             let name = method_name.ident.as_str();
             if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
@@ -129,19 +165,42 @@ fn collect_unwrap_info<'tcx>(
                     _ => unreachable!(),
                 };
                 let safe_to_unwrap = unwrappable != invert;
-                return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
+                let kind = if is_type_diagnostic_item(cx, ty, sym::option_type) {
+                    UnwrappableKind::Option
+                } else {
+                    UnwrappableKind::Result
+                };
+
+                return vec![
+                    UnwrapInfo {
+                        local_id,
+                        if_expr,
+                        check: expr,
+                        check_name: method_name,
+                        branch,
+                        safe_to_unwrap,
+                        kind,
+                        is_entire_condition,
+                    }
+                ]
             }
         }
     }
     Vec::new()
 }
 
 impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
-    fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
+    fn visit_branch(
+        &mut self,
+        if_expr: &'tcx Expr<'_>,
+        cond: &'tcx Expr<'_>,
+        branch: &'tcx Expr<'_>,
+        else_branch: bool,
+    ) {
         let prev_len = self.unwrappables.len();
-        for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
-            if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
-                || is_potentially_mutated(unwrap_info.ident, branch, self.cx)
+        for unwrap_info in collect_unwrap_info(self.cx, if_expr, cond, branch, else_branch, true) {
+            if is_potentially_mutated(unwrap_info.local_id, cond, self.cx)
+                || is_potentially_mutated(unwrap_info.local_id, branch, self.cx)
             {
                 // if the variable is mutated, we don't know whether it can be unwrapped:
                 continue;
@@ -163,32 +222,62 @@ impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
         }
         if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr) {
             walk_expr(self, cond);
-            self.visit_branch(cond, then, false);
+            self.visit_branch(expr, cond, then, false);
             if let Some(else_inner) = r#else {
-                self.visit_branch(cond, else_inner, true);
+                self.visit_branch(expr, cond, else_inner, true);
             }
         } else {
             // find `unwrap[_err]()` calls:
             if_chain! {
                 if let ExprKind::MethodCall(method_name, _, args, _) = expr.kind;
-                if let ExprKind::Path(QPath::Resolved(None, path)) = args[0].kind;
+                if let Some(id) = path_to_local(&args[0]);
                 if [sym::unwrap, sym::expect, sym!(unwrap_err)].contains(&method_name.ident.name);
                 let call_to_unwrap = [sym::unwrap, sym::expect].contains(&method_name.ident.name);
                 if let Some(unwrappable) = self.unwrappables.iter()
-                    .find(|u| u.ident.res == path.res);
+                    .find(|u| u.local_id == id);
                 // Span contexts should not differ with the conditional branch
                 if !differing_macro_contexts(unwrappable.branch.span, expr.span);
                 if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
                 then {
                     if call_to_unwrap == unwrappable.safe_to_unwrap {
+                        let is_entire_condition = unwrappable.is_entire_condition;
+                        let unwrappable_variable_name = self.cx.tcx.hir().name(unwrappable.local_id);
+                        let suggested_pattern = if call_to_unwrap {
+                            unwrappable.kind.success_variant_pattern()
+                        } else {
+                            unwrappable.kind.error_variant_pattern()
+                        };
+
                         span_lint_and_then(
                             self.cx,
                             UNNECESSARY_UNWRAP,
                             expr.span,
-                            &format!("you checked before that `{}()` cannot fail, \
-                            instead of checking and unwrapping, it's better to use `if let` or `match`",
-                            method_name.ident.name),
-                            |diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
+                            &format!(
+                                "called `{}` on `{}` after checking its variant with `{}`",
+                                method_name.ident.name,
+                                unwrappable_variable_name,
+                                unwrappable.check_name.ident.as_str(),
+                            ),
+                            |diag| {
+                                if is_entire_condition {
+                                    diag.span_suggestion(
+                                        unwrappable.check.span.with_lo(unwrappable.if_expr.span.lo()),
+                                        "try",
+                                        format!(
+                                            "if let {} = {}",
+                                            suggested_pattern,
+                                            unwrappable_variable_name,
+                                        ),
+                                        // We don't track how the unwrapped value is used inside the
+                                        // block or suggest deleting the unwrap, so we can't offer a
+                                        // fixable solution.
+                                        Applicability::Unspecified,
+                                    );
+                                } else {
+                                    diag.span_label(unwrappable.check.span, "the check is happening here");
+                                    diag.help("try using `if let` or `match`");
+                                }
+                            },
                         );
                     } else {
                         span_lint_and_then(

clippy_utils/src/usage.rs

@@ -1,10 +1,9 @@
 use crate as utils;
 use rustc_hir as hir;
-use rustc_hir::def::Res;
 use rustc_hir::intravisit;
 use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
 use rustc_hir::HirIdSet;
-use rustc_hir::{Expr, ExprKind, HirId, Path};
+use rustc_hir::{Expr, ExprKind, HirId};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
@@ -35,12 +34,8 @@ pub fn mutated_variables<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) ->
     Some(delegate.used_mutably)
 }
 
-pub fn is_potentially_mutated<'tcx>(variable: &'tcx Path<'_>, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
-    if let Res::Local(id) = variable.res {
-        mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&id))
-    } else {
-        true
-    }
+pub fn is_potentially_mutated<'tcx>(variable: HirId, expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) -> bool {
+    mutated_variables(expr, cx).map_or(true, |mutated| mutated.contains(&variable))
 }
 
 struct MutVarsDelegate {