Rollup merge of #150846 - thir-hir-id, r=lcnr

include `HirId`s directly in the THIR, not wrapped in `LintLevel`s

Occurrences of `LintLevel` in the THIR were always `LintLevel::Explicit`, containing a `HirId`, so we don't need to make it possible to put `LintLevel::Inherited` there. Removing the unused case where `HirId`s aren't present in the THIR slightly simplifies diagnostics/lints/tools that want to map from the THIR back to the HIR, e.g. #145569.

Since `LintLevel` is no longer present in the THIR, I've moved it in the second commit to live in `rustc_mir_build`; that's where it's actually used. I'm not sure exactly where exactly it should live there, but I put it in the `builder::scope` module since it's used by `Builder::in_scope` for determining when to introduce source scopes.

r? lcnr as the reviewer of #145569, since this was discussed there

Author: Zalathar

compiler/rustc_middle/src/thir.rs

@@ -116,12 +116,6 @@ pub struct Param<'tcx> {
     pub hir_id: Option<HirId>,
 }
 
-#[derive(Copy, Clone, Debug, HashStable)]
-pub enum LintLevel {
-    Inherited,
-    Explicit(HirId),
-}
-
 #[derive(Clone, Debug, HashStable)]
 pub struct Block {
     /// Whether the block itself has a label. Used by `label: {}`
@@ -236,8 +230,8 @@ pub enum StmtKind<'tcx> {
         /// `let pat: ty = <INIT> else { <ELSE> }`
         else_block: Option<BlockId>,
 
-        /// The lint level for this `let` statement.
-        lint_level: LintLevel,
+        /// The [`HirId`] for this `let` statement.
+        hir_id: HirId,
 
         /// Span of the `let <PAT> = <INIT>` part.
         span: Span,
@@ -271,7 +265,7 @@ pub enum ExprKind<'tcx> {
     /// and to track the `HirId` of the expressions within the scope.
     Scope {
         region_scope: region::Scope,
-        lint_level: LintLevel,
+        hir_id: HirId,
         value: ExprId,
     },
     /// A `box <value>` expression.
@@ -579,7 +573,7 @@ pub struct Arm<'tcx> {
     pub pattern: Box<Pat<'tcx>>,
     pub guard: Option<ExprId>,
     pub body: ExprId,
-    pub lint_level: LintLevel,
+    pub hir_id: HirId,
     pub scope: region::Scope,
     pub span: Span,
 }

compiler/rustc_middle/src/thir/visit.rs

@@ -47,9 +47,7 @@ pub fn walk_expr<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
     use ExprKind::*;
     let Expr { kind, ty: _, temp_scope_id: _, span: _ } = expr;
     match *kind {
-        Scope { value, region_scope: _, lint_level: _ } => {
-            visitor.visit_expr(&visitor.thir()[value])
-        }
+        Scope { value, region_scope: _, hir_id: _ } => visitor.visit_expr(&visitor.thir()[value]),
         Box { value } => visitor.visit_expr(&visitor.thir()[value]),
         If { cond, then, else_opt, if_then_scope: _ } => {
             visitor.visit_expr(&visitor.thir()[cond]);
@@ -205,7 +203,7 @@ pub fn walk_stmt<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
             remainder_scope: _,
             init_scope: _,
             pattern,
-            lint_level: _,
+            hir_id: _,
             else_block,
             span: _,
         } => {
@@ -238,7 +236,7 @@ pub fn walk_arm<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
     visitor: &mut V,
     arm: &'thir Arm<'tcx>,
 ) {
-    let Arm { guard, pattern, body, lint_level: _, span: _, scope: _ } = arm;
+    let Arm { guard, pattern, body, hir_id: _, span: _, scope: _ } = arm;
     if let Some(expr) = guard {
         visitor.visit_expr(&visitor.thir()[*expr])
     }

compiler/rustc_mir_build/src/builder/block.rs

@@ -7,6 +7,7 @@ use tracing::debug;
 
 use crate::builder::ForGuard::OutsideGuard;
 use crate::builder::matches::{DeclareLetBindings, ScheduleDrops};
+use crate::builder::scope::LintLevel;
 use crate::builder::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -83,7 +84,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     init_scope,
                     pattern,
                     initializer: Some(initializer),
-                    lint_level,
+                    hir_id,
                     else_block: Some(else_block),
                     span: _,
                 } => {
@@ -191,7 +192,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                     let initializer_span = this.thir[*initializer].span;
                     let scope = (*init_scope, source_info);
-                    let failure_and_block = this.in_scope(scope, *lint_level, |this| {
+                    let lint_level = LintLevel::Explicit(*hir_id);
+                    let failure_and_block = this.in_scope(scope, lint_level, |this| {
                         this.declare_bindings(
                             visibility_scope,
                             remainder_span,
@@ -232,7 +234,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     init_scope,
                     pattern,
                     initializer,
-                    lint_level,
+                    hir_id,
                     else_block: None,
                     span: _,
                 } => {
@@ -250,12 +252,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         Some(this.new_source_scope(remainder_span, LintLevel::Inherited));
 
                     // Evaluate the initializer, if present.
+                    let lint_level = LintLevel::Explicit(*hir_id);
                     if let Some(init) = *initializer {
                         let initializer_span = this.thir[init].span;
                         let scope = (*init_scope, source_info);
 
                         block = this
-                            .in_scope(scope, *lint_level, |this| {
+                            .in_scope(scope, lint_level, |this| {
                                 this.declare_bindings(
                                     visibility_scope,
                                     remainder_span,
@@ -269,7 +272,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             .into_block();
                     } else {
                         let scope = (*init_scope, source_info);
-                        let _: BlockAnd<()> = this.in_scope(scope, *lint_level, |this| {
+                        let _: BlockAnd<()> = this.in_scope(scope, lint_level, |this| {
                             this.declare_bindings(
                                 visibility_scope,
                                 remainder_span,

compiler/rustc_mir_build/src/builder/expr/as_constant.rs

@@ -23,7 +23,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let tcx = this.tcx;
         let Expr { ty, temp_scope_id: _, span, ref kind } = *expr;
         match kind {
-            ExprKind::Scope { region_scope: _, lint_level: _, value } => {
+            ExprKind::Scope { region_scope: _, hir_id: _, value } => {
                 this.as_constant(&this.thir[*value])
             }
             _ => as_constant_inner(

compiler/rustc_mir_build/src/builder/expr/as_operand.rs

@@ -6,6 +6,7 @@ use rustc_middle::thir::*;
 use tracing::{debug, instrument};
 
 use crate::builder::expr::category::Category;
+use crate::builder::scope::LintLevel;
 use crate::builder::{BlockAnd, BlockAndExtension, Builder, NeedsTemporary};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -122,10 +123,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let this = self; // See "LET_THIS_SELF".
 
         let expr = &this.thir[expr_id];
-        if let ExprKind::Scope { region_scope, lint_level, value } = expr.kind {
+        if let ExprKind::Scope { region_scope, hir_id, value } = expr.kind {
             let source_info = this.source_info(expr.span);
             let region_scope = (region_scope, source_info);
-            return this.in_scope(region_scope, lint_level, |this| {
+            return this.in_scope(region_scope, LintLevel::Explicit(hir_id), |this| {
                 this.as_operand(block, scope, value, local_info, needs_temporary)
             });
         }
@@ -165,10 +166,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let expr = &this.thir[expr_id];
         debug!("as_call_operand(block={:?}, expr={:?})", block, expr);
 
-        if let ExprKind::Scope { region_scope, lint_level, value } = expr.kind {
+        if let ExprKind::Scope { region_scope, hir_id, value } = expr.kind {
             let source_info = this.source_info(expr.span);
             let region_scope = (region_scope, source_info);
-            return this.in_scope(region_scope, lint_level, |this| {
+            return this.in_scope(region_scope, LintLevel::Explicit(hir_id), |this| {
                 this.as_call_operand(block, scope, value)
             });
         }

compiler/rustc_mir_build/src/builder/expr/as_place.rs

@@ -16,6 +16,7 @@ use tracing::{debug, instrument, trace};
 
 use crate::builder::ForGuard::{OutsideGuard, RefWithinGuard};
 use crate::builder::expr::category::Category;
+use crate::builder::scope::LintLevel;
 use crate::builder::{BlockAnd, BlockAndExtension, Builder, Capture, CaptureMap};
 
 /// The "outermost" place that holds this value.
@@ -427,8 +428,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let expr_span = expr.span;
         let source_info = this.source_info(expr_span);
         match expr.kind {
-            ExprKind::Scope { region_scope, lint_level, value } => {
-                this.in_scope((region_scope, source_info), lint_level, |this| {
+            ExprKind::Scope { region_scope, hir_id, value } => {
+                this.in_scope((region_scope, source_info), LintLevel::Explicit(hir_id), |this| {
                     this.expr_as_place(block, value, mutability, fake_borrow_temps)
                 })
             }

compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs

@@ -18,6 +18,7 @@ use tracing::debug;
 
 use crate::builder::expr::as_place::PlaceBase;
 use crate::builder::expr::category::{Category, RvalueFunc};
+use crate::builder::scope::LintLevel;
 use crate::builder::{BlockAnd, BlockAndExtension, Builder, NeedsTemporary};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -56,9 +57,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         match expr.kind {
             ExprKind::ThreadLocalRef(did) => block.and(Rvalue::ThreadLocalRef(did)),
-            ExprKind::Scope { region_scope, lint_level, value } => {
+            ExprKind::Scope { region_scope, hir_id, value } => {
                 let region_scope = (region_scope, source_info);
-                this.in_scope(region_scope, lint_level, |this| this.as_rvalue(block, scope, value))
+                this.in_scope(region_scope, LintLevel::Explicit(hir_id), |this| {
+                    this.as_rvalue(block, scope, value)
+                })
             }
             ExprKind::Repeat { value, count } => {
                 if Some(0) == count.try_to_target_usize(this.tcx) {
@@ -657,7 +660,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     source: eid,
                     is_from_as_cast: _,
                 }
-                | &ExprKind::Scope { region_scope: _, lint_level: _, value: eid } => {
+                | &ExprKind::Scope { region_scope: _, hir_id: _, value: eid } => {
                     kind = &self.thir[eid].kind
                 }
                 _ => return matches!(Category::of(&kind), Some(Category::Constant)),

compiler/rustc_mir_build/src/builder/expr/as_temp.rs

@@ -7,7 +7,7 @@ use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use tracing::{debug, instrument};
 
-use crate::builder::scope::DropKind;
+use crate::builder::scope::{DropKind, LintLevel};
 use crate::builder::{BlockAnd, BlockAndExtension, Builder};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -39,10 +39,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let expr = &this.thir[expr_id];
         let expr_span = expr.span;
         let source_info = this.source_info(expr_span);
-        if let ExprKind::Scope { region_scope, lint_level, value } = expr.kind {
-            return this.in_scope((region_scope, source_info), lint_level, |this| {
-                this.as_temp(block, temp_lifetime, value, mutability)
-            });
+        if let ExprKind::Scope { region_scope, hir_id, value } = expr.kind {
+            return this.in_scope(
+                (region_scope, source_info),
+                LintLevel::Explicit(hir_id),
+                |this| this.as_temp(block, temp_lifetime, value, mutability),
+            );
         }
 
         let expr_ty = expr.ty;

compiler/rustc_mir_build/src/builder/expr/into.rs

@@ -16,6 +16,7 @@ use tracing::{debug, instrument};
 
 use crate::builder::expr::category::{Category, RvalueFunc};
 use crate::builder::matches::{DeclareLetBindings, HasMatchGuard};
+use crate::builder::scope::LintLevel;
 use crate::builder::{BlockAnd, BlockAndExtension, BlockFrame, Builder, NeedsTemporary};
 use crate::errors::{LoopMatchArmWithGuard, LoopMatchUnsupportedType};
 
@@ -45,10 +46,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
 
         let block_and = match expr.kind {
-            ExprKind::Scope { region_scope, lint_level, value } => {
+            ExprKind::Scope { region_scope, hir_id, value } => {
                 let region_scope = (region_scope, source_info);
                 ensure_sufficient_stack(|| {
-                    this.in_scope(region_scope, lint_level, |this| {
+                    this.in_scope(region_scope, LintLevel::Explicit(hir_id), |this| {
                         this.expr_into_dest(destination, block, value)
                     })
                 })

compiler/rustc_mir_build/src/builder/expr/stmt.rs

@@ -5,7 +5,7 @@ use rustc_middle::thir::*;
 use rustc_span::source_map::Spanned;
 use tracing::debug;
 
-use crate::builder::scope::BreakableTarget;
+use crate::builder::scope::{BreakableTarget, LintLevel};
 use crate::builder::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -25,8 +25,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // Handle a number of expressions that don't need a destination at all. This
         // avoids needing a mountain of temporary `()` variables.
         match expr.kind {
-            ExprKind::Scope { region_scope, lint_level, value } => {
-                this.in_scope((region_scope, source_info), lint_level, |this| {
+            ExprKind::Scope { region_scope, hir_id, value } => {
+                this.in_scope((region_scope, source_info), LintLevel::Explicit(hir_id), |this| {
                     this.stmt_expr(block, value, statement_scope)
                 })
             }
@@ -106,7 +106,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
             ExprKind::Become { value } => {
                 let v = &this.thir[value];
-                let ExprKind::Scope { value, lint_level, region_scope } = v.kind else {
+                let ExprKind::Scope { value, hir_id, region_scope } = v.kind else {
                     span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}")
                 };
 
@@ -115,7 +115,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     span_bug!(v.span, "`thir_check_tail_calls` should have disallowed this {v:?}")
                 };
 
-                this.in_scope((region_scope, source_info), lint_level, |this| {
+                this.in_scope((region_scope, source_info), LintLevel::Explicit(hir_id), |this| {
                     let fun = unpack!(block = this.as_local_operand(block, fun));
                     let args: Box<[_]> = args
                         .into_iter()