Auto merge of rust-lang#120687 - oli-obk:early_const_prop, r=<try>

Run const_prop_lint in check builds, too

implements rust-lang#108730 (comment)

Turns the const_prop_lint pass into a query that is run alongside borrowck.

Author: bors

compiler/rustc_abi/src/layout.rs

@@ -426,10 +426,11 @@ where
                 }
             }
         }
-        _ => assert!(
-            start == Bound::Unbounded && end == Bound::Unbounded,
-            "nonscalar layout for layout_scalar_valid_range type: {st:#?}",
-        ),
+        _ => {
+            if start != Bound::Unbounded || end != Bound::Unbounded {
+                return None;
+            }
+        }
     }
 
     Some(st)

compiler/rustc_interface/src/passes.rs

@@ -738,6 +738,7 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> {
             // Run unsafety check because it's responsible for stealing and
             // deallocating THIR.
             tcx.ensure().check_unsafety(def_id);
+            tcx.ensure().const_prop_lint(def_id);
             tcx.ensure().mir_borrowck(def_id)
         });
     });

compiler/rustc_middle/src/query/erase.rs

@@ -241,6 +241,7 @@ trivial! {
     Option<rustc_target::spec::PanicStrategy>,
     Option<usize>,
     Result<(), rustc_errors::ErrorGuaranteed>,
+    Result<(), traits::util::HasImpossiblePredicates>,
     Result<(), rustc_middle::traits::query::NoSolution>,
     Result<rustc_middle::traits::EvaluationResult, rustc_middle::traits::OverflowError>,
     rustc_ast::expand::allocator::AllocatorKind,

compiler/rustc_middle/src/query/mod.rs

@@ -39,6 +39,7 @@ use crate::traits::query::{
     OutlivesBound,
 };
 use crate::traits::specialization_graph;
+use crate::traits::util::HasImpossiblePredicates;
 use crate::traits::{
     CodegenObligationError, EvaluationResult, ImplSource, ObjectSafetyViolation, ObligationCause,
     OverflowError, WellFormedLoc,
@@ -1018,6 +1019,12 @@ rustc_queries! {
         cache_on_disk_if(tcx) { tcx.is_typeck_child(key.to_def_id()) }
     }
 
+    /// Run the const prop lints on the `mir_promoted` of an item.
+    query const_prop_lint(key: LocalDefId) -> Result<(), HasImpossiblePredicates> {
+        desc { |tcx| "checking const prop lints for `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { true }
+    }
+
     /// Gets a complete map from all types to their inherent impls.
     /// Not meant to be used directly outside of coherence.
     query crate_inherent_impls(k: ()) -> Result<&'tcx CrateInherentImpls, ErrorGuaranteed> {

compiler/rustc_middle/src/traits/util.rs

@@ -46,3 +46,9 @@ impl<'tcx> Iterator for Elaborator<'tcx> {
         }
     }
 }
+
+/// Used as an error type to signal that an item may have an invalid body, because its
+/// where bounds are trivially not satisfyable.
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(HashStable, Encodable, Decodable)]
+pub struct HasImpossiblePredicates;

compiler/rustc_mir_transform/src/lib.rs

@@ -40,6 +40,7 @@ use rustc_middle::mir::{
     SourceInfo, Statement, StatementKind, TerminatorKind, START_BLOCK,
 };
 use rustc_middle::query::Providers;
+use rustc_middle::traits::util::HasImpossiblePredicates;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
 use rustc_span::{source_map::Spanned, sym, DUMMY_SP};
 use rustc_trait_selection::traits;
@@ -142,6 +143,7 @@ pub fn provide(providers: &mut Providers) {
         is_ctfe_mir_available: |tcx, did| is_mir_available(tcx, did),
         mir_callgraph_reachable: inline::cycle::mir_callgraph_reachable,
         mir_inliner_callees: inline::cycle::mir_inliner_callees,
+        const_prop_lint,
         promoted_mir,
         deduced_param_attrs: deduce_param_attrs::deduced_param_attrs,
         ..*providers
@@ -398,28 +400,11 @@ fn inner_mir_for_ctfe(tcx: TyCtxt<'_>, def: LocalDefId) -> Body<'_> {
     body
 }
 
-/// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
-/// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
-/// end up missing the source MIR due to stealing happening.
-fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
-    if tcx.is_coroutine(def.to_def_id()) {
-        tcx.ensure_with_value().mir_coroutine_witnesses(def);
-    }
-    let mir_borrowck = tcx.mir_borrowck(def);
-
-    let is_fn_like = tcx.def_kind(def).is_fn_like();
-    if is_fn_like {
-        // Do not compute the mir call graph without said call graph actually being used.
-        if pm::should_run_pass(tcx, &inline::Inline) {
-            tcx.ensure_with_value().mir_inliner_callees(ty::InstanceDef::Item(def.to_def_id()));
-        }
-    }
-
+fn const_prop_lint(tcx: TyCtxt<'_>, def: LocalDefId) -> Result<(), HasImpossiblePredicates> {
     let (body, _) = tcx.mir_promoted(def);
-    let mut body = body.steal();
-    if let Some(error_reported) = mir_borrowck.tainted_by_errors {
-        body.tainted_by_errors = Some(error_reported);
-    }
+    let body = body.borrow();
+
+    let mir_borrowck = tcx.mir_borrowck(def);
 
     // Check if it's even possible to satisfy the 'where' clauses
     // for this item.
@@ -455,6 +440,40 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
         .iter()
         .filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
     if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
+        Err(HasImpossiblePredicates)
+    } else {
+        if mir_borrowck.tainted_by_errors.is_none() && body.tainted_by_errors.is_none() {
+            const_prop_lint::ConstPropLint.run_lint(tcx, &body);
+        }
+        Ok(())
+    }
+}
+
+/// Obtain just the main MIR (no promoteds) and run some cleanups on it. This also runs
+/// mir borrowck *before* doing so in order to ensure that borrowck can be run and doesn't
+/// end up missing the source MIR due to stealing happening.
+fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
+    if tcx.is_coroutine(def.to_def_id()) {
+        tcx.ensure_with_value().mir_coroutine_witnesses(def);
+    }
+    let mir_borrowck = tcx.mir_borrowck(def);
+    let has_impossible_predicates = tcx.const_prop_lint(def);
+
+    let is_fn_like = tcx.def_kind(def).is_fn_like();
+    if is_fn_like {
+        // Do not compute the mir call graph without said call graph actually being used.
+        if pm::should_run_pass(tcx, &inline::Inline) {
+            tcx.ensure_with_value().mir_inliner_callees(ty::InstanceDef::Item(def.to_def_id()));
+        }
+    }
+
+    let (body, _) = tcx.mir_promoted(def);
+    let mut body = body.steal();
+    if let Some(error_reported) = mir_borrowck.tainted_by_errors {
+        body.tainted_by_errors = Some(error_reported);
+    }
+
+    if let Err(HasImpossiblePredicates) = has_impossible_predicates {
         trace!("found unsatisfiable predicates for {:?}", body.source);
         // Clear the body to only contain a single `unreachable` statement.
         let bbs = body.basic_blocks.as_mut();
@@ -538,7 +557,6 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         &elaborate_box_derefs::ElaborateBoxDerefs,
         &coroutine::StateTransform,
         &add_retag::AddRetag,
-        &Lint(const_prop_lint::ConstPropLint),
     ];
     pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));
 }

src/doc/rustc/src/lints/levels.md

@@ -71,7 +71,7 @@ level is capped via cap-lints.
 A 'deny' lint produces an error if you violate it. For example, this code
 runs into the `exceeding_bitshifts` lint.
 
-```rust,no_run
+```rust,compile_fail
 fn main() {
     100u8 << 10;
 }
@@ -246,7 +246,7 @@ pub fn foo() {}
 This is the maximum level for all lints. So for example, if we take our
 code sample from the "deny" lint level above:
 
-```rust,no_run
+```rust,compile_fail
 fn main() {
     100u8 << 10;
 }

src/tools/clippy/tests/ui-toml/suppress_lint_in_const/test.rs

@@ -35,9 +35,8 @@ fn main() {
     x[const { idx() }]; // Ok, should not produce stderr.
     x[const { idx4() }]; // Ok, let rustc's `unconditional_panic` lint handle `usize` indexing on arrays.
     const { &ARR[idx()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
-    const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
-    //
-    //~^^ ERROR: failed
+    // FIXME errors in rustc and subsequently blocks all lints in this file. Can reenable once solved on the rustc side
+    //const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
 
     let y = &x;
     y[0]; // Ok, referencing shouldn't affect this lint. See the issue 6021

src/tools/clippy/tests/ui-toml/suppress_lint_in_const/test.stderr

@@ -1,15 +1,3 @@
-error[E0080]: evaluation of `main::{constant#3}` failed
-  --> $DIR/test.rs:38:14
-   |
-LL |     const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
-   |              ^^^^^^^^^^^ index out of bounds: the length is 2 but the index is 4
-
-note: erroneous constant encountered
-  --> $DIR/test.rs:38:5
-   |
-LL |     const { &ARR[idx4()] }; // Ok, should not produce stderr, since `suppress-restriction-lint-in-const` is set true.
-   |     ^^^^^^^^^^^^^^^^^^^^^^
-
 error: indexing may panic
   --> $DIR/test.rs:29:5
    |
@@ -21,39 +9,39 @@ LL |     x[index];
    = help: to override `-D warnings` add `#[allow(clippy::indexing_slicing)]`
 
 error: indexing may panic
-  --> $DIR/test.rs:47:5
+  --> $DIR/test.rs:46:5
    |
 LL |     v[0];
    |     ^^^^
    |
    = help: consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic
-  --> $DIR/test.rs:48:5
+  --> $DIR/test.rs:47:5
    |
 LL |     v[10];
    |     ^^^^^
    |
    = help: consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic
-  --> $DIR/test.rs:49:5
+  --> $DIR/test.rs:48:5
    |
 LL |     v[1 << 3];
    |     ^^^^^^^^^
    |
    = help: consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic
-  --> $DIR/test.rs:55:5
+  --> $DIR/test.rs:54:5
    |
 LL |     v[N];
    |     ^^^^
    |
    = help: consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic
-  --> $DIR/test.rs:56:5
+  --> $DIR/test.rs:55:5
    |
 LL |     v[M];
    |     ^^^^
@@ -66,6 +54,6 @@ error[E0080]: evaluation of constant value failed
 LL | const REF_ERR: &i32 = &ARR[idx4()]; // Ok, let rustc handle const contexts.
    |                        ^^^^^^^^^^^ index out of bounds: the length is 2 but the index is 4
 
-error: aborting due to 8 previous errors
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0080`.

src/tools/clippy/tests/ui/indexing_slicing_index.rs

@@ -45,8 +45,8 @@ fn main() {
     const { &ARR[idx()] };
     //~^ ERROR: indexing may panic
     // This should be linted, since `suppress-restriction-lint-in-const` default is false.
-    const { &ARR[idx4()] };
-    //~^ ERROR: indexing may panic
+    // FIXME can't include here for now, as the error on it causes all lints to get silenced
+    //const { &ARR[idx4()] };
 
     let y = &x;
     // Ok, referencing shouldn't affect this lint. See the issue 6021