Auto merge of rust-lang#79328 - c410-f3r:hir-if, r=matthewjasper

Reintroduce hir::ExprKind::If

Basically copied and paste rust-lang#59288/rust-lang/rust-clippy#4080 with some modifications.

The vast majority of tests were fixed and now there are only a few remaining. Since I am still unable to figure out the missing pieces, any help with the following list is welcome.

- [ ] **Unnecessary `typeck` exception**: [Cheated on this one to make CI green.](https://github.com/rust-lang/rust/pull/79328/files#diff-3faee9ba23fc54a12b7c43364ba81f8c5660045c7e1d7989a02a0cee1c5b2051)
- [x] **Incorrect span**: [Span should reference `then` and `else` separately.](https://github.com/rust-lang/rust/pull/79328/files#diff-cf2c46e82222ee4b1037a68fff8a1af3c4f1de7a6b3fd798aacbf3c0475abe3d)
- [x] **New note regarding `assert!`**: [Modified but not "wrong". Maybe can be a good thing?](https://github.com/rust-lang/rust/pull/79328/files#diff-9e0d7c89ed0224e2b62060c957177c27db43c30dfe3c2974cb6b5091cda9cfb5)
- [x] **Inverted report location**: [Modified but not "wrong". Locations were inverted.](https://github.com/rust-lang/rust/pull/79328/files#diff-f637ce7c1f68d523a165aa9651765df05e36c4d7d279194b1a6b28b48a323691)
- [x] **`src/test/ui/point-to-type-err-cause-on-impl-trait-return.rs` has weird errors**: [Not sure why this is happening.](https://github.com/rust-lang/rust/pull/79328/files#diff-c823c09660f5b112f95e97e8ff71f1797b6c7f37dbb3d16f8e98bbaea8072e95)
- [x] **Missing diagnostic**: [???](https://github.com/rust-lang/rust/pull/79328/files#diff-6b8ab09360d725ba4513933827f9796b42ff9522b0690f80b76de067143af2fc)

clippy_lints/src/assertions_on_constants.rs

@@ -1,8 +1,7 @@
 use crate::consts::{constant, Constant};
 use crate::utils::{is_direct_expn_of, is_expn_of, match_panic_call, snippet_opt, span_lint_and_help};
 use if_chain::if_chain;
-use rustc_ast::ast::LitKind;
-use rustc_hir::{Expr, ExprKind, PatKind, UnOp};
+use rustc_hir::{Expr, ExprKind, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 
@@ -102,31 +101,22 @@ enum AssertKind {
 /// Check if the expression matches
 ///
 /// ```rust,ignore
-/// match { let _t = !c; _t } {
-///     true => {
-///         {
-///             ::std::rt::begin_panic(message, _)
-///         }
-///     }
-///     _ => { }
-/// };
+/// if !c {
+///   {
+///     ::std::rt::begin_panic(message, _)
+///   }
+/// }
 /// ```
 ///
 /// where `message` is any expression and `c` is a constant bool.
 fn match_assert_with_message<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<AssertKind> {
     if_chain! {
-        if let ExprKind::Match(ref expr, ref arms, _) = expr.kind;
-        // matches { let _t = expr; _t }
-        if let ExprKind::DropTemps(ref expr) = expr.kind;
-        if let ExprKind::Unary(UnOp::UnNot, ref expr) = expr.kind;
+        if let ExprKind::If(ref cond, ref then, _) = expr.kind;
+        if let ExprKind::Unary(UnOp::UnNot, ref expr) = cond.kind;
         // bind the first argument of the `assert!` macro
         if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.typeck_results(), expr);
-        // arm 1 pattern
-        if let PatKind::Lit(ref lit_expr) = arms[0].pat.kind;
-        if let ExprKind::Lit(ref lit) = lit_expr.kind;
-        if let LitKind::Bool(true) = lit.node;
-        // arm 1 block
-        if let ExprKind::Block(ref block, _) = arms[0].body.kind;
+        // block
+        if let ExprKind::Block(ref block, _) = then.kind;
         if block.stmts.is_empty();
         if let Some(block_expr) = &block.expr;
         // inner block is optional. unwrap it if it exists, or use the expression as is otherwise.

clippy_lints/src/blocks_in_if_conditions.rs

@@ -1,4 +1,4 @@
-use crate::utils::{differing_macro_contexts, higher, snippet_block_with_applicability, span_lint, span_lint_and_sugg};
+use crate::utils::{differing_macro_contexts, snippet_block_with_applicability, span_lint, span_lint_and_sugg};
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
@@ -75,7 +75,7 @@ impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
         if in_external_macro(cx.sess(), expr.span) {
             return;
         }
-        if let Some((cond, _, _)) = higher::if_block(&expr) {
+        if let ExprKind::If(cond, _, _) = &expr.kind {
             if let ExprKind::Block(block, _) = &cond.kind {
                 if block.rules == BlockCheckMode::DefaultBlock {
                     if block.stmts.is_empty() {

clippy_lints/src/cognitive_complexity.rs

@@ -147,6 +147,9 @@ impl<'tcx> Visitor<'tcx> for CCHelper {
     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
         walk_expr(self, e);
         match e.kind {
+            ExprKind::If(_, _, _) => {
+                self.cc += 1;
+            },
             ExprKind::Match(_, ref arms, _) => {
                 if arms.len() > 1 {
                     self.cc += 1;

clippy_lints/src/consts.rs

@@ -1,6 +1,6 @@
 #![allow(clippy::float_cmp)]
 
-use crate::utils::{clip, higher, sext, unsext};
+use crate::utils::{clip, sext, unsext};
 use if_chain::if_chain;
 use rustc_ast::ast::{FloatTy, LitFloatType, LitKind};
 use rustc_data_structures::sync::Lrc;
@@ -228,9 +228,6 @@ pub struct ConstEvalLateContext<'a, 'tcx> {
 impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
     /// Simple constant folding: Insert an expression, get a constant or none.
     pub fn expr(&mut self, e: &Expr<'_>) -> Option<Constant> {
-        if let Some((ref cond, ref then, otherwise)) = higher::if_block(&e) {
-            return self.ifthenelse(cond, then, otherwise);
-        }
         match e.kind {
             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.typeck_results.expr_ty(e)),
             ExprKind::Block(ref block, _) => self.block(block),
@@ -249,6 +246,7 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
                 UnOp::UnNeg => self.constant_negate(&o, self.typeck_results.expr_ty(e)),
                 UnOp::UnDeref => Some(if let Constant::Ref(r) = o { *r } else { o }),
             }),
+            ExprKind::If(ref cond, ref then, ref otherwise) => self.ifthenelse(cond, then, *otherwise),
             ExprKind::Binary(op, ref left, ref right) => self.binop(op, left, right),
             ExprKind::Call(ref callee, ref args) => {
                 // We only handle a few const functions for now.

clippy_lints/src/copies.rs

@@ -1,6 +1,6 @@
 use crate::utils::{eq_expr_value, in_macro, search_same, SpanlessEq, SpanlessHash};
-use crate::utils::{get_parent_expr, higher, if_sequence, span_lint_and_note};
-use rustc_hir::{Block, Expr};
+use crate::utils::{get_parent_expr, if_sequence, span_lint_and_note};
+use rustc_hir::{Block, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 
@@ -109,11 +109,12 @@ impl<'tcx> LateLintPass<'tcx> for CopyAndPaste {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if !expr.span.from_expansion() {
             // skip ifs directly in else, it will be checked in the parent if
-            if let Some(expr) = get_parent_expr(cx, expr) {
-                if let Some((_, _, Some(ref else_expr))) = higher::if_block(&expr) {
-                    if else_expr.hir_id == expr.hir_id {
-                        return;
-                    }
+            if let Some(&Expr {
+                kind: ExprKind::If(_, _, Some(ref else_expr)),
+                ..
+            }) = get_parent_expr(cx, expr) {
+                if else_expr.hir_id == expr.hir_id {
+                    return;
                 }
             }
 

clippy_lints/src/entry.rs

@@ -1,5 +1,5 @@
 use crate::utils::SpanlessEq;
-use crate::utils::{get_item_name, higher, is_type_diagnostic_item, match_type, paths, snippet, snippet_opt};
+use crate::utils::{get_item_name, is_type_diagnostic_item, match_type, paths, snippet, snippet_opt};
 use crate::utils::{snippet_with_applicability, span_lint_and_then};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
@@ -54,7 +54,7 @@ declare_lint_pass!(HashMapPass => [MAP_ENTRY]);
 
 impl<'tcx> LateLintPass<'tcx> for HashMapPass {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
+        if let ExprKind::If(ref check, ref then_block, ref else_block) = expr.kind {
             if let ExprKind::Unary(UnOp::UnNot, ref check) = check.kind {
                 if let Some((ty, map, key)) = check_cond(cx, check) {
                     // in case of `if !m.contains_key(&k) { m.insert(k, v); }`

clippy_lints/src/floating_point_arithmetic.rs

@@ -2,7 +2,7 @@ use crate::consts::{
     constant, constant_simple, Constant,
     Constant::{Int, F32, F64},
 };
-use crate::utils::{eq_expr_value, get_parent_expr, higher, numeric_literal, span_lint_and_sugg, sugg};
+use crate::utils::{eq_expr_value, get_parent_expr, numeric_literal, span_lint_and_sugg, sugg};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
@@ -556,11 +556,11 @@ fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a
 
 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
     if_chain! {
-        if let Some((cond, body, Some(else_body))) = higher::if_block(&expr);
+        if let ExprKind::If(cond, body, else_body) = expr.kind;
         if let ExprKind::Block(block, _) = body.kind;
         if block.stmts.is_empty();
         if let Some(if_body_expr) = block.expr;
-        if let ExprKind::Block(else_block, _) = else_body.kind;
+        if let Some(ExprKind::Block(else_block, _)) = else_body.map(|el| &el.kind);
         if else_block.stmts.is_empty();
         if let Some(else_body_expr) = else_block.expr;
         if let Some((if_expr_positive, body)) = are_negated(cx, if_body_expr, else_body_expr);

clippy_lints/src/implicit_return.rs

@@ -81,6 +81,13 @@ fn expr_match(cx: &LateContext<'_>, expr: &Expr<'_>) {
                 lint(cx, expr.span, break_expr.span, LINT_BREAK);
             }
         },
+        ExprKind::If(.., if_expr, else_expr) => {
+            expr_match(cx, if_expr);
+
+            if let Some(else_expr) = else_expr {
+                expr_match(cx, else_expr);
+            }
+        },
         ExprKind::Match(.., arms, source) => {
             let check_all_arms = match source {
                 MatchSource::IfLetDesugar {

clippy_lints/src/implicit_saturating_sub.rs

@@ -1,4 +1,4 @@
-use crate::utils::{higher, in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
+use crate::utils::{in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
@@ -42,7 +42,7 @@ impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingSub {
             return;
         }
         if_chain! {
-            if let Some((ref cond, ref then, None)) = higher::if_block(&expr);
+            if let ExprKind::If(cond, then, None) = &expr.kind;
 
             // Check if the conditional expression is a binary operation
             if let ExprKind::Binary(ref cond_op, ref cond_left, ref cond_right) = cond.kind;

clippy_lints/src/let_if_seq.rs

@@ -1,5 +1,4 @@
-use crate::utils::visitors::LocalUsedVisitor;
-use crate::utils::{higher, qpath_res, snippet, span_lint_and_then};
+use crate::utils::{qpath_res, snippet, span_lint_and_then, visitors::LocalUsedVisitor};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -64,7 +63,7 @@ impl<'tcx> LateLintPass<'tcx> for LetIfSeq {
                 if let hir::StmtKind::Local(ref local) = stmt.kind;
                 if let hir::PatKind::Binding(mode, canonical_id, ident, None) = local.pat.kind;
                 if let hir::StmtKind::Expr(ref if_) = expr.kind;
-                if let Some((ref cond, ref then, ref else_)) = higher::if_block(&if_);
+                if let hir::ExprKind::If(ref cond, ref then, ref else_) = if_.kind;
                 if !LocalUsedVisitor::new(canonical_id).check_expr(cond);
                 if let hir::ExprKind::Block(ref then, _) = then.kind;
                 if let Some(value) = check_assign(cx, canonical_id, &*then);

clippy_lints/src/loops.rs

@@ -742,6 +742,14 @@ fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
             // Break can come from the inner loop so remove them.
             absorb_break(&never_loop_block(b, main_loop_id))
         },
+        ExprKind::If(ref e, ref e2, ref e3) => {
+            let e1 = never_loop_expr(e, main_loop_id);
+            let e2 = never_loop_expr(e2, main_loop_id);
+            let e3 = e3
+                .as_ref()
+                .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
+            combine_seq(e1, combine_branches(e2, e3))
+        },
         ExprKind::Match(ref e, ref arms, _) => {
             let e = never_loop_expr(e, main_loop_id);
             if arms.is_empty() {
@@ -2594,7 +2602,7 @@ fn is_loop(expr: &Expr<'_>) -> bool {
 }
 
 fn is_conditional(expr: &Expr<'_>) -> bool {
-    matches!(expr.kind, ExprKind::Match(..))
+    matches!(expr.kind, ExprKind::If(..) | ExprKind::Match(..))
 }
 
 fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {

clippy_lints/src/manual_strip.rs

@@ -80,7 +80,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualStrip {
         }
 
         if_chain! {
-            if let Some((cond, then, _)) = higher::if_block(&expr);
+            if let ExprKind::If(cond, then, _) = &expr.kind;
             if let ExprKind::MethodCall(_, _, [target_arg, pattern], _) = cond.kind;
             if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
             if let ExprKind::Path(target_path) = &target_arg.kind;

clippy_lints/src/methods/mod.rs

@@ -2048,6 +2048,7 @@ fn lint_expect_fun_call(
             hir::ExprKind::Call(..)
             | hir::ExprKind::MethodCall(..)
             // These variants are debatable or require further examination
+            | hir::ExprKind::If(..)
             | hir::ExprKind::Match(..)
             | hir::ExprKind::Block{ .. } => true,
             _ => false,

clippy_lints/src/methods/unnecessary_filter_map.rs

@@ -90,6 +90,12 @@ fn check_expression<'tcx>(cx: &LateContext<'tcx>, arg_id: hir::HirId, expr: &'tc
             }
             (found_mapping, found_filtering)
         },
+        // There must be an else_arm or there will be a type error
+        hir::ExprKind::If(_, ref if_arm, Some(ref else_arm)) => {
+            let if_check = check_expression(cx, arg_id, if_arm);
+            let else_check = check_expression(cx, arg_id, else_arm);
+            (if_check.0 | else_check.0, if_check.1 | else_check.1)
+        },
         hir::ExprKind::Path(path) if match_qpath(path, &paths::OPTION_NONE) => (false, true),
         _ => (true, true),
     }

clippy_lints/src/mutable_debug_assertion.rs

@@ -90,6 +90,10 @@ impl<'a, 'tcx> Visitor<'tcx> for MutArgVisitor<'a, 'tcx> {
                 self.found = true;
                 return;
             },
+            ExprKind::If(..) => {
+                self.found = true;
+                return;
+            },
             ExprKind::Path(_) => {
                 if let Some(adj) = self.cx.typeck_results().adjustments().get(expr.hir_id) {
                     if adj

clippy_lints/src/needless_bool.rs

@@ -4,7 +4,7 @@
 
 use crate::utils::sugg::Sugg;
 use crate::utils::{
-    higher, is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg,
+    is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg,
 };
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
@@ -71,7 +71,7 @@ declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
 impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
         use self::Expression::{Bool, RetBool};
-        if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
+        if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.kind {
             let reduce = |ret, not| {
                 let mut applicability = Applicability::MachineApplicable;
                 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);

clippy_lints/src/option_if_let_else.rs

@@ -109,25 +109,26 @@ fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
 /// it in curly braces. Otherwise, we don't.
 fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
+        let mut should_wrap = false;
+
         if let Some(Expr {
             kind:
                 ExprKind::Match(
                     _,
                     arms,
-                    MatchSource::IfDesugar {
-                        contains_else_clause: true,
-                    }
-                    | MatchSource::IfLetDesugar {
+                    MatchSource::IfLetDesugar {
                         contains_else_clause: true,
                     },
                 ),
             ..
         }) = parent.expr
         {
-            expr.hir_id == arms[1].body.hir_id
-        } else {
-            false
+            should_wrap = expr.hir_id == arms[1].body.hir_id;
+        } else if let Some(Expr { kind: ExprKind::If(_, _, Some(else_clause)), .. }) = parent.expr {
+            should_wrap = expr.hir_id == else_clause.hir_id;
         }
+
+        should_wrap
     })
 }
 

clippy_lints/src/question_mark.rs

@@ -8,7 +8,7 @@ use rustc_span::sym;
 
 use crate::utils::sugg::Sugg;
 use crate::utils::{
-    eq_expr_value, higher, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet_with_applicability,
+    eq_expr_value, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet_with_applicability,
     span_lint_and_sugg,
 };
 
@@ -50,7 +50,7 @@ impl QuestionMark {
     /// If it matches, it will suggest to use the question mark operator instead
     fn check_is_none_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
         if_chain! {
-            if let Some((if_expr, body, else_)) = higher::if_block(&expr);
+            if let ExprKind::If(if_expr, body, else_) = &expr.kind;
             if let ExprKind::MethodCall(segment, _, args, _) = &if_expr.kind;
             if segment.ident.name == sym!(is_none);
             if Self::expression_returns_none(cx, body);

clippy_lints/src/returns.rs

@@ -184,6 +184,14 @@ fn check_final_expr<'tcx>(
         ExprKind::Block(ref block, _) => {
             check_block_return(cx, block);
         },
+        ExprKind::If(_, then, else_clause_opt) => {
+            if let ExprKind::Block(ref ifblock, _) = then.kind {
+                check_block_return(cx, ifblock);
+            }
+            if let Some(else_clause) = else_clause_opt {
+                check_final_expr(cx, else_clause, None, RetReplacement::Empty);
+            }
+        },
         // a match expr, check all arms
         // an if/if let expr, check both exprs
         // note, if without else is going to be a type checking error anyways
@@ -194,9 +202,6 @@ fn check_final_expr<'tcx>(
                     check_final_expr(cx, &arm.body, Some(arm.body.span), RetReplacement::Block);
                 }
             },
-            MatchSource::IfDesugar {
-                contains_else_clause: true,
-            }
             | MatchSource::IfLetDesugar {
                 contains_else_clause: true,
             } => {

clippy_lints/src/shadow.rs

@@ -333,6 +333,13 @@ fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, bindings: &mut
                 check_expr(cx, e, bindings)
             }
         },
+        ExprKind::If(ref cond, ref then, ref otherwise) => {
+            check_expr(cx, cond, bindings);
+            check_expr(cx, &**then, bindings);
+            if let Some(ref o) = *otherwise {
+                check_expr(cx, o, bindings);
+            }
+        },
         ExprKind::Match(ref init, arms, _) => {
             check_expr(cx, init, bindings);
             let len = bindings.len();