Rollup merge of #61518 - czipperz:const-fn-doc-disallow-loops, r=Centril

Add loops to doc list of things not stable in const fn

Closes #61508

diff --combined src/librustc_mir/transform/qualify_min_const_fn.rs
index f96675864562f3b410773183e4dadf0ba255e4eb,ff4459dd3577f74504b441af8fff789d2ab7b29c..7bafef79acd1a48ef5e18ce9ff6d5e3c4aea0b2b
--- 1/src/librustc_mir/transform/qualify_min_const_fn.rs
--- 2/src/librustc_mir/transform/qualify_min_const_fn.rs
+++ b/src/librustc_mir/transform/qualify_min_const_fn.rs
@@@ -11,7 -11,7 +11,7 @@@ type McfResult = Result<(), (Span, Cow<
  pub fn is_min_const_fn(
      tcx: TyCtxt<'a, 'tcx, 'tcx>,
      def_id: DefId,
 -    mir: &'a Body<'tcx>,
 +    body: &'a Body<'tcx>,
  ) -> McfResult {
      let mut current = def_id;
      loop {
@@@ -59,21 -59,21 +59,21 @@@
          }
      }
  
 -    for local in &mir.local_decls {
 +    for local in &body.local_decls {
          check_ty(tcx, local.ty, local.source_info.span, def_id)?;
      }
      // impl trait is gone in MIR, so check the return type manually
      check_ty(
          tcx,
          tcx.fn_sig(def_id).output().skip_binder(),
 -        mir.local_decls.iter().next().unwrap().source_info.span,
 +        body.local_decls.iter().next().unwrap().source_info.span,
          def_id,
      )?;
  
 -    for bb in mir.basic_blocks() {
 -        check_terminator(tcx, mir, bb.terminator())?;
 +    for bb in body.basic_blocks() {
 +        check_terminator(tcx, body, bb.terminator())?;
          for stmt in &bb.statements {
 -            check_statement(tcx, mir, stmt)?;
 +            check_statement(tcx, body, stmt)?;
          }
      }
      Ok(())
@@@ -130,7 -130,7 +130,7 @@@ fn check_ty
  
  fn check_rvalue(
      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 -    mir: &'a Body<'tcx>,
 +    body: &'a Body<'tcx>,
      rvalue: &Rvalue<'tcx>,
      span: Span,
  ) -> McfResult {
@@@ -143,7 -143,7 +143,7 @@@
          }
          Rvalue::Cast(CastKind::Misc, operand, cast_ty) => {
              use rustc::ty::cast::CastTy;
 -            let cast_in = CastTy::from_ty(operand.ty(mir, tcx)).expect("bad input type for cast");
 +            let cast_in = CastTy::from_ty(operand.ty(body, tcx)).expect("bad input type for cast");
              let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
              match (cast_in, cast_out) {
                  (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => Err((
@@@ -173,7 -173,7 +173,7 @@@
          Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => {
              check_operand(lhs, span)?;
              check_operand(rhs, span)?;
 -            let ty = lhs.ty(mir, tcx);
 +            let ty = lhs.ty(body, tcx);
              if ty.is_integral() || ty.is_bool() || ty.is_char() {
                  Ok(())
              } else {
@@@ -189,7 -189,7 +189,7 @@@
              "heap allocations are not allowed in const fn".into(),
          )),
          Rvalue::UnaryOp(_, operand) => {
 -            let ty = operand.ty(mir, tcx);
 +            let ty = operand.ty(body, tcx);
              if ty.is_integral() || ty.is_bool() {
                  check_operand(operand, span)
              } else {
@@@ -210,14 -210,14 +210,14 @@@
  
  fn check_statement(
      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 -    mir: &'a Body<'tcx>,
 +    body: &'a Body<'tcx>,
      statement: &Statement<'tcx>,
  ) -> McfResult {
      let span = statement.source_info.span;
      match &statement.kind {
          StatementKind::Assign(place, rval) => {
              check_place(place, span)?;
 -            check_rvalue(tcx, mir, rval, span)
 +            check_rvalue(tcx, body, rval, span)
          }
  
          StatementKind::FakeRead(_, place) => check_place(place, span),
@@@ -280,7 -280,7 +280,7 @@@ fn check_place
  
  fn check_terminator(
      tcx: TyCtxt<'a, 'tcx, 'tcx>,
 -    mir: &'a Body<'tcx>,
 +    body: &'a Body<'tcx>,
      terminator: &Terminator<'tcx>,
  ) -> McfResult {
      let span = terminator.source_info.span;
@@@ -299,7 -299,7 +299,7 @@@
  
          TerminatorKind::FalseEdges { .. } | TerminatorKind::SwitchInt { .. } => Err((
              span,
-             "`if`, `match`, `&&` and `||` are not stable in const fn".into(),
+             "loops and conditional expressions are not stable in const fn".into(),
          )),
          | TerminatorKind::Abort | TerminatorKind::Unreachable => {
              Err((span, "const fn with unreachable code is not stable".into()))
@@@ -315,7 -315,7 +315,7 @@@
              destination: _,
              cleanup: _,
          } => {
 -            let fn_ty = func.ty(mir, tcx);
 +            let fn_ty = func.ty(body, tcx);
              if let ty::FnDef(def_id, _) = fn_ty.sty {
  
                  // some intrinsics are waved through if called inside the