Fix Clippy with changed for loop desugar

Author: camsteffen

src/tools/clippy/clippy_lints/src/loops/explicit_counter_loop.rs

@@ -1,6 +1,4 @@
-use super::{
-    get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP,
-};
+use super::{make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::{get_enclosing_block, is_integer_const};
@@ -37,12 +35,10 @@ pub(super) fn check<'tcx>(
                 then {
                     let mut applicability = Applicability::MachineApplicable;
 
-                    let for_span = get_span_of_entire_for_loop(expr);
-
                     span_lint_and_sugg(
                         cx,
                         EXPLICIT_COUNTER_LOOP,
-                        for_span.with_hi(arg.span.hi()),
+                        expr.span.with_hi(arg.span.hi()),
                         &format!("the variable `{}` is used as a loop counter", name),
                         "consider using",
                         format!(

src/tools/clippy/clippy_lints/src/loops/manual_memcpy.rs

@@ -1,4 +1,4 @@
-use super::{get_span_of_entire_for_loop, IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
+use super::{IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet;
 use clippy_utils::sugg::Sugg;
@@ -86,7 +86,7 @@ pub(super) fn check<'tcx>(
                 span_lint_and_sugg(
                     cx,
                     MANUAL_MEMCPY,
-                    get_span_of_entire_for_loop(expr),
+                    expr.span,
                     "it looks like you're manually copying between slices",
                     "try replacing the loop by",
                     big_sugg,

src/tools/clippy/clippy_lints/src/loops/mod.rs

@@ -23,7 +23,7 @@ use rustc_hir::{Expr, ExprKind, LoopSource, Pat};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use utils::{get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor};
+use utils::{make_iterator_snippet, IncrementVisitor, InitializeVisitor};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -566,14 +566,25 @@ declare_lint_pass!(Loops => [
 impl<'tcx> LateLintPass<'tcx> for Loops {
     #[allow(clippy::too_many_lines)]
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some(higher::ForLoop { pat, arg, body, span }) = higher::ForLoop::hir(expr) {
+        let for_loop = higher::ForLoop::hir(expr);
+        if let Some(higher::ForLoop {
+            pat,
+            arg,
+            body,
+            loop_id,
+            span,
+        }) = for_loop
+        {
             // we don't want to check expanded macros
             // this check is not at the top of the function
             // since higher::for_loop expressions are marked as expansions
             if body.span.from_expansion() {
                 return;
             }
             check_for_loop(cx, pat, arg, body, expr, span);
+            if let ExprKind::Block(block, _) = body.kind {
+                never_loop::check(cx, block, loop_id, span, for_loop.as_ref());
+            }
         }
 
         // we don't want to check expanded macros
@@ -582,7 +593,9 @@ impl<'tcx> LateLintPass<'tcx> for Loops {
         }
 
         // check for never_loop
-        never_loop::check(cx, expr);
+        if let ExprKind::Loop(block, ..) = expr.kind {
+            never_loop::check(cx, block, expr.hir_id, expr.span, None);
+        }
 
         // check for `loop { if let {} else break }` that could be `while let`
         // (also matches an explicit "match" instead of "if let")

src/tools/clippy/clippy_lints/src/loops/never_loop.rs

@@ -4,35 +4,41 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::ForLoop;
 use clippy_utils::source::snippet;
 use rustc_errors::Applicability;
-use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, LoopSource, Node, Pat, Stmt, StmtKind};
+use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Pat, Stmt, StmtKind};
 use rustc_lint::LateContext;
+use rustc_span::Span;
 use std::iter::{once, Iterator};
 
-pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-    if let ExprKind::Loop(block, _, source, _) = expr.kind {
-        match never_loop_block(block, expr.hir_id) {
-            NeverLoopResult::AlwaysBreak => {
-                span_lint_and_then(cx, NEVER_LOOP, expr.span, "this loop never actually loops", |diag| {
-                    if_chain! {
-                        if source == LoopSource::ForLoop;
-                        if let Some((_, Node::Expr(parent_match))) = cx.tcx.hir().parent_iter(expr.hir_id).nth(1);
-                        if let Some(ForLoop { arg: iterator, pat, span: for_span, .. }) = ForLoop::hir(parent_match);
-                        then {
-                            // Suggests using an `if let` instead. This is `Unspecified` because the
-                            // loop may (probably) contain `break` statements which would be invalid
-                            // in an `if let`.
-                            diag.span_suggestion_verbose(
-                                for_span.with_hi(iterator.span.hi()),
-                                "if you need the first element of the iterator, try writing",
-                                for_to_if_let_sugg(cx, iterator, pat),
-                                Applicability::Unspecified,
-                            );
-                        }
-                    };
-                });
-            },
-            NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
-        }
+pub(super) fn check(
+    cx: &LateContext<'tcx>,
+    block: &'tcx Block<'_>,
+    loop_id: HirId,
+    span: Span,
+    for_loop: Option<&ForLoop<'_>>,
+) {
+    match never_loop_block(block, loop_id) {
+        NeverLoopResult::AlwaysBreak => {
+            span_lint_and_then(cx, NEVER_LOOP, span, "this loop never actually loops", |diag| {
+                if let Some(ForLoop {
+                    arg: iterator,
+                    pat,
+                    span: for_span,
+                    ..
+                }) = for_loop
+                {
+                    // Suggests using an `if let` instead. This is `Unspecified` because the
+                    // loop may (probably) contain `break` statements which would be invalid
+                    // in an `if let`.
+                    diag.span_suggestion_verbose(
+                        for_span.with_hi(iterator.span.hi()),
+                        "if you need the first element of the iterator, try writing",
+                        for_to_if_let_sugg(cx, iterator, pat),
+                        Applicability::Unspecified,
+                    );
+                }
+            });
+        },
+        NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
     }
 }
 

src/tools/clippy/clippy_lints/src/loops/single_element_loop.rs

@@ -1,4 +1,4 @@
-use super::{get_span_of_entire_for_loop, SINGLE_ELEMENT_LOOP};
+use super::SINGLE_ELEMENT_LOOP;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::single_segment_path;
 use clippy_utils::source::{indent_of, snippet};
@@ -30,7 +30,6 @@ pub(super) fn check<'tcx>(
         if !block.stmts.is_empty();
 
         then {
-            let for_span = get_span_of_entire_for_loop(expr);
             let mut block_str = snippet(cx, block.span, "..").into_owned();
             block_str.remove(0);
             block_str.pop();
@@ -39,7 +38,7 @@ pub(super) fn check<'tcx>(
             span_lint_and_sugg(
                 cx,
                 SINGLE_ELEMENT_LOOP,
-                for_span,
+                expr.span,
                 "for loop over a single element",
                 "try",
                 format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),

src/tools/clippy/clippy_lints/src/loops/utils.rs

@@ -7,7 +7,6 @@ use rustc_hir::HirIdMap;
 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Stmt, StmtKind};
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
-use rustc_span::source_map::Span;
 use rustc_span::symbol::{sym, Symbol};
 use std::iter::Iterator;
 
@@ -300,17 +299,6 @@ impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
     }
 }
 
-// this function assumes the given expression is a `for` loop.
-pub(super) fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
-    // for some reason this is the only way to get the `Span`
-    // of the entire `for` loop
-    if let ExprKind::Match(_, arms, _) = &expr.kind {
-        arms[0].body.span
-    } else {
-        unreachable!()
-    }
-}
-
 /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
 /// actual `Iterator` that the loop uses.
 pub(super) fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {

src/tools/clippy/clippy_lints/src/misc.rs

@@ -20,8 +20,8 @@ use rustc_span::symbol::sym;
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
-    expr_path_res, get_item_name, get_parent_expr, higher, in_constant, is_diag_trait_item, is_integer_const,
-    iter_input_pats, last_path_segment, match_any_def_paths, paths, unsext, SpanlessEq,
+    expr_path_res, get_item_name, get_parent_expr, in_constant, is_diag_trait_item, is_integer_const, iter_input_pats,
+    last_path_segment, match_any_def_paths, paths, unsext, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -312,7 +312,6 @@ impl<'tcx> LateLintPass<'tcx> for MiscLints {
             if let StmtKind::Local(local) = stmt.kind;
             if let PatKind::Binding(an, .., name, None) = local.pat.kind;
             if let Some(init) = local.init;
-            if !higher::is_from_for_desugar(local);
             if an == BindingAnnotation::Ref || an == BindingAnnotation::RefMut;
             then {
                 // use the macro callsite when the init span (but not the whole local span)

src/tools/clippy/clippy_lints/src/unit_types/let_unit_value.rs

@@ -1,5 +1,4 @@
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::higher;
 use clippy_utils::source::snippet_with_macro_callsite;
 use rustc_errors::Applicability;
 use rustc_hir::{Stmt, StmtKind};
@@ -14,9 +13,6 @@ pub(super) fn check(cx: &LateContext<'_>, stmt: &Stmt<'_>) {
             if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
                 return;
             }
-            if higher::is_from_for_desugar(local) {
-                return;
-            }
             span_lint_and_then(
                 cx,
                 LET_UNIT_VALUE,

src/tools/clippy/clippy_utils/src/higher.rs

@@ -22,31 +22,31 @@ pub struct ForLoop<'tcx> {
     pub arg: &'tcx hir::Expr<'tcx>,
     /// `for` loop body
     pub body: &'tcx hir::Expr<'tcx>,
+    /// Compare this against `hir::Destination.target`
+    pub loop_id: HirId,
     /// entire `for` loop span
     pub span: Span,
 }
 
 impl<'tcx> ForLoop<'tcx> {
-    #[inline]
     /// Parses a desugared `for` loop
     pub fn hir(expr: &Expr<'tcx>) -> Option<Self> {
         if_chain! {
-            if let hir::ExprKind::Match(iterexpr, arms, hir::MatchSource::ForLoopDesugar) = expr.kind;
-            if let Some(first_arm) = arms.get(0);
-            if let hir::ExprKind::Call(_, iterargs) = iterexpr.kind;
-            if let Some(first_arg) = iterargs.get(0);
-            if iterargs.len() == 1 && arms.len() == 1 && first_arm.guard.is_none();
-            if let hir::ExprKind::Loop(block, ..) = first_arm.body.kind;
-            if block.expr.is_none();
-            if let [ _, _, ref let_stmt, ref body ] = *block.stmts;
-            if let hir::StmtKind::Local(local) = let_stmt.kind;
-            if let hir::StmtKind::Expr(body_expr) = body.kind;
+            if let hir::ExprKind::DropTemps(e) = expr.kind;
+            if let hir::ExprKind::Match(iterexpr, [arm], hir::MatchSource::ForLoopDesugar) = e.kind;
+            if let hir::ExprKind::Call(_, [arg]) = iterexpr.kind;
+            if let hir::ExprKind::Loop(block, ..) = arm.body.kind;
+            if let [stmt] = &*block.stmts;
+            if let hir::StmtKind::Expr(e) = stmt.kind;
+            if let hir::ExprKind::Match(_, [_, some_arm], _) = e.kind;
+            if let hir::PatKind::Struct(_, [field], _) = some_arm.pat.kind;
             then {
                 return Some(Self {
-                    pat: &*local.pat,
-                    arg: first_arg,
-                    body: body_expr,
-                    span: first_arm.span
+                    pat: field.pat,
+                    arg,
+                    body: some_arm.body,
+                    loop_id: arm.body.hir_id,
+                    span: expr.span.ctxt().outer_expn_data().call_site,
                 });
             }
         }
@@ -678,38 +678,6 @@ impl<'tcx> FormatArgsArg<'tcx> {
     }
 }
 
-/// Checks if a `let` statement is from a `for` loop desugaring.
-pub fn is_from_for_desugar(local: &hir::Local<'_>) -> bool {
-    // This will detect plain for-loops without an actual variable binding:
-    //
-    // ```
-    // for x in some_vec {
-    //     // do stuff
-    // }
-    // ```
-    if_chain! {
-        if let Some(expr) = local.init;
-        if let hir::ExprKind::Match(_, _, hir::MatchSource::ForLoopDesugar) = expr.kind;
-        then {
-            return true;
-        }
-    }
-
-    // This detects a variable binding in for loop to avoid `let_unit_value`
-    // lint (see issue #1964).
-    //
-    // ```
-    // for _ in vec![()] {
-    //     // anything
-    // }
-    // ```
-    if let hir::LocalSource::ForLoopDesugar = local.source {
-        return true;
-    }
-
-    false
-}
-
 /// A parsed `panic!` expansion
 pub struct PanicExpn<'tcx> {
     /// Span of `panic!(..)`

src/tools/clippy/tests/ui/author/for_loop.stdout

@@ -11,11 +11,8 @@ if_chain! {
     // unimplemented: field checks
     if arms.len() == 1;
     if let ExprKind::Loop(ref body, ref label, LoopSource::ForLoop) = arms[0].body.kind;
-    if body.stmts.len() == 4;
-    if let StmtKind::Local(ref local) = body.stmts[0].kind;
-    if let PatKind::Binding(BindingAnnotation::Mutable, _, name, None) = local.pat.kind;
-    if name.as_str() == "__next";
-    if let StmtKind::Expr(ref e, _) = body.stmts[1].kind
+    if body.stmts.len() == 1;
+    if let StmtKind::Expr(ref e, _) = body.stmts[0].kind
     if let ExprKind::Match(ref expr2, ref arms1, MatchSource::ForLoopDesugar) = e.kind;
     if let ExprKind::Call(ref func1, ref args1) = expr2.kind;
     if let ExprKind::Path(ref path2) = func1.kind;
@@ -25,39 +22,27 @@ if_chain! {
     if let ExprKind::Path(ref path3) = inner.kind;
     if match_qpath(path3, &["iter"]);
     if arms1.len() == 2;
-    if let ExprKind::Assign(ref target, ref value, ref _span) = arms1[0].body.kind;
-    if let ExprKind::Path(ref path4) = target.kind;
-    if match_qpath(path4, &["__next"]);
-    if let ExprKind::Path(ref path5) = value.kind;
-    if match_qpath(path5, &["val"]);
-    if let PatKind::Struct(ref path6, ref fields1, false) = arms1[0].pat.kind;
-    if matches!(path6, QPath::LangItem(LangItem::OptionSome, _));
-    if fields1.len() == 1;
-    // unimplemented: field checks
-    if let ExprKind::Break(ref destination, None) = arms1[1].body.kind;
-    if let PatKind::Struct(ref path7, ref fields2, false) = arms1[1].pat.kind;
-    if matches!(path7, QPath::LangItem(LangItem::OptionNone, _));
-    if fields2.len() == 0;
+    if let ExprKind::Break(ref destination, None) = arms1[0].body.kind;
+    if let PatKind::Struct(ref path4, ref fields1, false) = arms1[0].pat.kind;
+    if matches!(path4, QPath::LangItem(LangItem::OptionNone, _));
+    if fields1.len() == 0;
     // unimplemented: field checks
-    if let StmtKind::Local(ref local1) = body.stmts[2].kind;
-    if let Some(ref init) = local1.init;
-    if let ExprKind::Path(ref path8) = init.kind;
-    if match_qpath(path8, &["__next"]);
-    if let PatKind::Binding(BindingAnnotation::Unannotated, _, name1, None) = local1.pat.kind;
-    if name1.as_str() == "y";
-    if let StmtKind::Expr(ref e1, _) = body.stmts[3].kind
-    if let ExprKind::Block(ref block) = e1.kind;
+    if let ExprKind::Block(ref block) = arms1[1].body.kind;
     if block.stmts.len() == 1;
-    if let StmtKind::Local(ref local2) = block.stmts[0].kind;
-    if let Some(ref init1) = local2.init;
-    if let ExprKind::Path(ref path9) = init1.kind;
-    if match_qpath(path9, &["y"]);
-    if let PatKind::Binding(BindingAnnotation::Unannotated, _, name2, None) = local2.pat.kind;
-    if name2.as_str() == "z";
+    if let StmtKind::Local(ref local) = block.stmts[0].kind;
+    if let Some(ref init) = local.init;
+    if let ExprKind::Path(ref path5) = init.kind;
+    if match_qpath(path5, &["y"]);
+    if let PatKind::Binding(BindingAnnotation::Unannotated, _, name, None) = local.pat.kind;
+    if name.as_str() == "z";
     if block.expr.is_none();
+    if let PatKind::Struct(ref path6, ref fields2, false) = arms1[1].pat.kind;
+    if matches!(path6, QPath::LangItem(LangItem::OptionSome, _));
+    if fields2.len() == 1;
+    // unimplemented: field checks
     if body.expr.is_none();
-    if let PatKind::Binding(BindingAnnotation::Mutable, _, name3, None) = arms[0].pat.kind;
-    if name3.as_str() == "iter";
+    if let PatKind::Binding(BindingAnnotation::Mutable, _, name1, None) = arms[0].pat.kind;
+    if name1.as_str() == "iter";
     then {
         // report your lint here
     }