structure and inductive commands

• #5517 improves universe level inference for the resulting type of an inductive or structure. Recall that a Prop-valued inductive type is a syntactic subsingleton if it has at most one constructor and all the arguments to the constructor are in Prop. Such types have large elimination, so they could be defined in Type or Prop without any trouble. The way inference has changed is that if a type is a syntactic subsingleton with exactly one constructor, and the constructor has at least one parameter/field, then the inductive/structure command will prefer creating a Prop instead of a Type. The upshot is that the : Prop in structure S : Prop is often no longer needed. (With @arthur-adjedj).

• #5842 and #5783 implement a feature where the structure command can now define recursive inductive types:

  structure Tree where
    n : Nat
    children : Fin n → Tree
  
  def Tree.size : Tree → Nat
    | {n, children} => Id.run do
      let mut s := 0
      for h : i in [0 : n] do
        s := s + (children ⟨i, h.2⟩).size
      pure s
  

• #5814 fixes a bug where Mathlib's Type* elaborator could lead to incorrect universe parameters with the inductive command.

• #3152 and #5844 fix bugs in default value processing for structure instance notation (with @arthur-adjedj).

• #5399 promotes instance synthesis order calculation failure from a soft error to a hard error.

• #5542 deprecates := variants of inductive and structure (see breaking changes).

Application elaboration improvements

• #5671 makes @[elab_as_elim] require at least one discriminant, since otherwise there is no advantage to this alternative elaborator.

• #5528 enables field notation in explicit mode. The syntax @x.f elaborates as @S.f with x supplied to the appropriate parameter.

• #5692 modifies the dot notation resolution algorithm so that it can apply CoeFun instances. For example, Mathlib has Multiset.card : Multiset α →+ Nat, and now with m : Multiset α, the notation m.card resolves to ⇑Multiset.card m.

• #5658 fixes a bug where 'don't know how to synthesize implicit argument' errors might have the incorrect local context when the eta arguments feature is activated.

• #5933 fixes a bug where .. ellipses in patterns made use of optparams and autoparams.

• #5770 makes dot notation for structures resolve using all ancestors. Adds a resolution order for generalized field notation. This is the order of namespaces visited during resolution when trying to resolve names. The algorithm to compute a resolution order is the commonly used C3 linearization (used for example by Python), which when successful ensures that immediate parents' namespaces are considered before more distant ancestors' namespaces. By default we use a relaxed version of the algorithm that tolerates inconsistencies, but using set_option structure.strictResolutionOrder true makes inconsistent parent orderings into warnings.

Recursion and induction principles

• #5619 fixes functional induction principle generation to avoid over-eta-expanding in the preprocessing step.

• #5766 fixes structural nested recursion so that it is not confused when a nested type appears first.

• #5803 fixes a bug in functional induction principle generation when there are let bindings.

• #5904 improves functional induction principle generation to unfold aux definitions more carefully.

• #5850 refactors code for Predefinition.Structural.

Error messages

• #5276 fixes a bug in "type mismatch" errors that would structurally assign metavariables during the algorithm to expose differences.

• #5919 makes "type mismatch" errors add type ascriptions to expose differences for numeric literals.

• #5922 makes "type mismatch" errors expose differences in the bodies of functions and pi types.

• #5888 improves the error message for invalid induction alternative names in match expressions (@josojo).

• #5719 improves calc error messages.

#5627 and #5663 improve the #eval command and introduce some new features.

• Now results can be pretty printed if there is a ToExpr instance, which means hoverable output. If ToExpr fails, it then tries looking for a Repr or ToString instance like before. Setting set_option eval.pp false disables making use of ToExpr instances.

• There is now auto-derivation of Repr instances, enabled with the pp.derive.repr option (default to true). For example:

  inductive Baz
  | a | b
  
  #eval Baz.a
  -- Baz.a
  

  It simply does deriving instance Repr for Baz when there's no way to represent Baz.

• The option eval.type controls whether or not to include the type in the output. For now the default is false.

• Now expressions such as #eval do return 2, where monad is unknown, work. It tries unifying the monad with CommandElabM, TermElabM, or IO.

• The classes Lean.Eval and Lean.MetaEval have been removed. These each used to be responsible for adapting monads and printing results. Now the MonadEval class is responsible for adapting monads for evaluation (it is similar to MonadLift, but instances are allowed to use default data when initializing state), and representing results is handled through a separate process.

• Error messages about failed instance synthesis are now more precise. Once it detects that a MonadEval class applies, then the error message will be specific about missing ToExpr/Repr/ToString instances.

• Fixes bugs where evaluating MetaM and CoreM wouldn't collect log messages.

• Fixes a bug where let rec could not be used in #eval.

partial definitions

• #5780 improves the error message when partial fails to prove a type is inhabited. Add delta deriving.

• #5821 gives partial inhabitation the ability to create local Inhabited instances from parameters.

New tactic configuration syntax. The configuration syntax for all core tactics has been given an upgrade. Rather than simp (config := { contextual := true, maxSteps := 22}), one can now write simp +contextual (maxSteps := 22). Tactic authors can migrate by switching from (config)? to optConfig in tactic syntaxes and potentially deleting mkOptionalNode in elaborators. #5883, #5898, #5928, and #5932. (Tactic authors, see breaking changes.)

simp tactic

• #5632 fixes the simpproc for Fin literals to reduce more consistently.

• #5648 fixes a bug in simpa ... using t where metavariables in t were not properly accounted for, and also improves the type mismatch error.

• #5838 fixes the docstring of simp! to actually talk about simp!.

• #5870 adds support for attribute [simp ←] (note the reverse direction). This adds the reverse of a theorem as a global simp theorem.

decide tactic

• #5665 adds decide! tactic for using kernel reduction (warning: this is renamed to decide +kernel in a future release).

bv_decide tactic

• #5714 adds inequality regression tests (@alexkeizer).

• #5608 adds bv_toNat tag for toNat_ofInt (@bollu).

• #5618 adds support for at in ac_nf and uses it in bv_normalize (@tobiasgrosser).

• #5628 adds udiv support.

• #5635 adds auxiliary bitblasters for negation and subtraction.

• #5637 adds more getLsbD bitblaster theory.

• #5652 adds umod support.

• #5653 adds performance benchmark for modulo.

• #5655 reduces error on bv_check to warning.

• #5670 adds ~~~(-x) support.

• #5673 disables ac_nf by default.

• #5675 fixes context tracking in bv_decide counter example.

• #5676 adds an error when the LRAT proof is invalid.

• #5781 introduces uninterpreted symbols everywhere.

• #5823 adds BitVec.sdiv support.

• #5852 adds BitVec.ofBool support.

• #5855 adds if support.

• #5869 adds support for all the SMTLIB BitVec divison/remainder operations.

• #5886 adds embedded constraint substitution.

• #5918 fixes loose mvars bug in bv_normalize.

• Documentation:

  • #5636 adds remarks about multiplication.

conv mode

• #5861 improves the congr conv tactic to handle "over-applied" functions.

• #5894 improves the arg conv tactic so that it can access more arguments and so that it can handle "over-applied" functions (it generates a specialized congruence lemma for the specific argument in question). Makes arg 1 and arg 2 apply to pi types in more situations. Adds negative indexing, for example arg -2 is equivalent to the lhs tactic. Makes the enter [...] tactic show intermediate states like rw.

Other tactics

• #4846 fixes a bug where generalize ... at * would apply to implementation details (@ymherklotz).

• #5730 upstreams the classical tactic combinator.

• #5815 improves the error message when trying to unfold a local hypothesis that is not a local definition.

• #5862 and #5863 change how apply and simp elaborate, making them not disable error recovery. This improves hovers and completions when the term has elaboration errors.

deriving clauses

• #5899 adds declaration ranges for delta-derived instances.

• #5265 removes unused syntax in deriving clauses for providing arguments to deriving handlers (see breaking changes).

#5065 upstreams and updates #where, a command that reports the current scope information.

Linters

• #5338 makes the unused variables linter ignore variables defined in tactics by default now, avoiding performance bottlenecks.

• #5644 ensures that linters in general do not run on #guard_msgs itself.

Metaprogramming interface

• #5720 adds pushGoal/pushGoals and popGoal for manipulating the goal state. These are an alternative to replaceMainGoal and getMainGoal, and with them you don't need to worry about making sure nothing clears assigned metavariables from the goal list between assigning the main goal and using replaceMainGoal. Modifies closeMainGoalUsing, which is like a TacticM version of liftMetaTactic. Now the callback is run in a context where the main goal is removed from the goal list, and the callback is free to modify the goal list. Furthermore, the checkUnassigned argument has been replaced with checkNewUnassigned, which checks whether the value assigned to the goal has any new metavariables, relative to the start of execution of the callback. Modifies withCollectingNewGoalsFrom to take the parentTag argument explicitly rather than indirectly via getMainTag. Modifies elabTermWithHoles to optionally take parentTag?.

• #5563 fixes getFunInfo and inferType to use withAtLeastTransparency rather than withTransparency.

• #5679 fixes RecursorVal.getInduct to return the name of major argument’s type. This makes "structure eta" work for nested inductives.

• #5681 removes unused mkRecursorInfoForKernelRec.

• #5686 makes discrimination trees index the domains of foralls, for better performance of the simplify and type class search.

• #5760 adds Lean.Expr.name? recognizer for Name expressions.

• #5800 modifies liftCommandElabM to preserve more state, fixing an issue where using it would drop messages.

• #5857 makes it possible to use dot notation in m! strings, for example m!"{.ofConstName n}".

• #5841 and #5853 record the complete list of structure parents in the StructureInfo environment extension.

Other fixes or improvements

• #5566 fixes a bug introduced in #4781 where heartbeat exceptions were no longer being handled properly. Now such exceptions are tagged with runtime.maxHeartbeats (@eric-wieser).

• #5708 modifies the proof objects produced by the proof-by-reflection tactics ac_nf0 and simp_arith so that the kernel is less prone to reducing expensive atoms.

• #5768 adds a #version command that prints Lean's version information.

• #5822 fixes elaborator algorithms to match kernel algorithms for primitive projections (Expr.proj).

• #5811 improves the docstring for the rwa tactic.

#5224 fixes WorkspaceClientCapabilities to make applyEdit optional, in accordance with the LSP specification (@pzread).

#5340 fixes a server deadlock when shutting down the language server and a desync between client and language server after a file worker crash.

#5560 makes initialize and builtin_initialize participate in the call hierarchy and other requests.

#5650 makes references in attributes participate in the call hierarchy and other requests.

#5666 add auto-completion in tactic blocks without having to type the first character of the tactic, and adds tactic completion docs to tactic auto-completion items.

#5677 fixes several cases where goal states were not displayed in certain text cursor positions.

#5707 indicates deprecations in auto-completion items.

#5736, #5752, #5763, #5802, and #5805 fix various performance issues in the language server.

#5801 distinguishes theorem auto-completions from non-theorem auto-completions.

#5640 fixes a bug where goal states in messages might print newlines as spaces.

#5643 adds option pp.mvars.delayed (default false), which when false causes delayed assignment metavariables to pretty print with what they are assigned to. Now fun x : Nat => ?a pretty prints as fun x : Nat => ?a rather than fun x ↦ ?m.7 x.

#5711 adds options pp.mvars.anonymous and pp.mvars.levels, which when false respectively cause expression metavariables and level metavariables to pretty print as ?_.

#5710 adjusts the ⋯ elaboration warning to mention pp.maxSteps.

#5759 fixes the app unexpander for sorryAx.

#5827 improves accuracy of binder names in the signature pretty printer (like in output of #check). Also fixes the issue where consecutive hygienic names pretty print without a space separating them, so we now have (x✝ y✝ : Nat) rather than (x✝y✝ : Nat).

#5830 makes sure all the core delaborators respond to pp.explicit when appropriate.

#5639 makes sure name literals use escaping when pretty printing.

#5854 adds delaborators for <|>, <*>, >>, <*, and *>.

Array

• #5687 deprecates Array.data.

• #5705 uses a better default value for Array.swapAt!.

• #5748 moves Array.mapIdx lemmas to a new file.

• #5749 simplifies signature of Array.mapIdx.

• #5758 upstreams Array.reduceOption.

• #5786 adds simp lemmas for Array.isEqv and BEq.

• #5796 renames Array.shrink to Array.take, and relates it to List.take.

• #5798 upstreams List.modify, adds lemmas, relates to Array.modify.

• #5799 relates Array.forIn and List.forIn.

• #5833 adds Array.forIn', and relates to List.

• #5848 fixes deprecations in Init.Data.Array.Basic to not recommend the deprecated constant.

• #5895 adds LawfulBEq (Array α) ↔ LawfulBEq α.

• #5896 moves @[simp] from back_eq_back? to back_push.

• #5897 renames Array.back to back!.

List

• #5605 removes List.redLength.

• #5696 upstreams List.mapIdx and adds lemmas.

• #5697 upstreams List.foldxM_map.

• #5701 renames List.join to List.flatten.

• #5703 upstreams List.sum.

• #5706 marks prefix_append_right_inj as a simp lemma.

• #5716 fixes List.drop_drop addition order.

• #5731 renames List.bind and Array.concatMap to flatMap.

• #5732 renames List.pure to List.singleton.

• #5742 upstreams ne_of_mem_of_not_mem.

• #5743 upstreams ne_of_apply_ne.

• #5816 adds more List.modify lemmas.

• #5879 renames List.groupBy to splitBy.

• #5913 relates for loops over List with foldlM.

Nat

• #5694 removes instBEqNat, which is redundant with instBEqOfDecidableEq but not defeq.

• #5746 deprecates Nat.sum.

• #5785 adds Nat.forall_lt_succ and variants.

Fixed width integers

• #5323 redefine unsigned fixed width integers in terms of BitVec.

• #5735 adds UIntX.[val_ofNat, toBitVec_ofNat].

• #5790 defines Int8.

• #5901 removes native code for UInt8.modn.

BitVec

• #5604 completes BitVec.[getMsbD|getLsbD|msb] for shifts (@luisacicolini).

• #5609 adds lemmas for division when denominator is zero (@bollu).

• #5620 documents Bitblasting (@bollu)

• #5623 moves BitVec.udiv/umod/sdiv/smod after add/sub/mul/lt (@tobiasgrosser).

• #5645 defines udiv normal form to be /, resp. umod and % (@bollu).

• #5646 adds lemmas about arithmetic inequalities (@bollu).

• #5680 expands relationship with toFin (@tobiasgrosser).

• #5691 adds BitVec.(getMSbD, msb)_(add, sub) and BitVec.getLsbD_sub (@luisacicolini).

• #5712 adds BitVec.[udiv|umod]_[zero|one|self] (@tobiasgrosser).

• #5718 adds BitVec.sdiv_[zero|one|self] (@tobiasgrosser).

• #5721 adds BitVec.(msb, getMsbD, getLsbD)_(neg, abs) (@luisacicolini).

• #5772 adds BitVec.toInt_sub, simplifies BitVec.toInt_neg (@tobiasgrosser).

• #5778 prove that intMin the smallest signed bitvector (@alexkeizer).

• #5851 adds (msb, getMsbD)_twoPow (@luisacicolini).

• #5858 adds BitVec.[zero_ushiftRight|zero_sshiftRight|zero_mul] and cleans up BVDecide (@tobiasgrosser).

• #5865 adds BitVec.(msb, getMsbD)_concat (@luisacicolini).

• #5881 adds Hashable (BitVec n)

String/Char

• #5728 upstreams String.dropPrefix?.

• #5745 changes String.dropPrefix? signature.

• #5747 adds Hashable Char instance

HashMap

• #5880 adds interim implementation of HashMap.modify/alter

Other

• #5704 removes @[simp] from Option.isSome_eq_isSome.

• #5739 upstreams material on Prod.

• #5740 moves Antisymm to Std.Antisymm.

• #5741 upstreams basic material on Sum.

• #5756 adds Nat.log2_two_pow (@spinylobster).

• #5892 removes duplicated ForIn instances.

• #5900 removes @[simp] from Sum.forall and Sum.exists.

• #5812 removes redundant Decidable assumptions (@FR-vdash-bot).

#5685 fixes help message flags, removes the -f flag and adds the -g flag (@James-Oswald).

#5930 adds --short-version (-V) option to display short version (@juhp).

#5144 switches all 64-bit platforms over to consistently using GMP for bignum arithmetic.

#5753 raises the minimum supported Windows version to Windows 10 1903 (released May 2019).

#5715 changes lake new math to use autoImplicit false (@eric-wieser).

#5688 makes Lake not create core aliases in the Lake namespace.

#5924 adds a text option for buildFile* utilities.

#5789 makes lake init not git init when inside git work tree (@haoxins).

#5684 has Lake update a package's lean-toolchain file on lake update if it finds the package's direct dependencies use a newer compatible toolchain. To skip this step, use the --keep-toolchain CLI option. (See breaking changes.)

#6218 makes Lake no longer automatically fetch GitHub cloud releases if the package build directory is already present (mirroring the behavior of the Reservoir cache). This prevents the cache from clobbering existing prebuilt artifacts. Users can still manually fetch the cache and clobber the build directory by running lake build <pkg>:release.

#6231 improves the errors Lake produces when it fails to fetch a dependency from Reservoir. If the package is not indexed, it will produce a suggestion about how to require it from GitHub.

#5617 fixes MSYS2 build instructions.

#5725 points out that OfScientific is called with raw literals (@eric-wieser).

#5794 adds a stub for application ellipsis notation (@eric-wieser).

The syntax for providing arguments to deriving handlers has been removed, which was not used by any major Lean projects in the ecosystem. As a result, the applyDerivingHandlers now takes one fewer argument, registerDerivingHandlerWithArgs is now simply registerDerivingHandler, DerivingHandler no longer includes the unused parameter, and DerivingHandlerNoArgs has been deprecated. To migrate code, delete the unused none argument and use registerDerivingHandler and DerivingHandler. (#5265)

The minimum supported Windows version has been raised to Windows 10 1903, released May 2019. (#5753)

The --lean CLI option for lake was removed. Use the LEAN environment variable instead. (#5684)

The inductive ... :=, structure ... :=, and class ... := syntaxes have been deprecated in favor of the ... where variants. The old syntax produces a warning, controlled by the linter.deprecated option. (#5542)

The generated tactic configuration elaborators now land in TacticM to make use of the current recovery state. Commands that wish to elaborate configurations should now use declare_command_config_elab instead of declare_config_elab to get an elaborator landing in CommandElabM. Syntaxes should migrate to optConfig instead of (config)?, but the elaborators are reverse compatible. (#5883)