This PR adds a `deprecated_module` command that marks the current module
as deprecated. When another module imports a deprecated module, a
warning is emitted during elaboration suggesting replacement imports.
Example usage:
```lean
deprecated_module "use NewModule instead" (since := "2026-03-30")
```
The warning message is optional but recommended. The `since` parameter
is required. Warnings can be disabled, by setting
`linter.deprecated.module` option to false in the command line. Because
the check happens when importing , using `set_option
linter.deprecated.module` in the source file won't affect the warnings.
Instead, a whole file can be marked not to display depreciation
warnings, by putting a comment `deprecated_module: ignore` next to
`module` keyword. Similarly, individual keywords can be silenced.
A `#show_deprecated_modules` command is also provided for inspecting
which modules in the current environment are deprecated.
`linter.deprecated.module` has no effect on this command, and hence one
can view deprecated modules, even when having warnings silenced.
This PR adds a `@[deprecated_arg]` attribute that marks individual
function parameters as deprecated. When a caller uses the old parameter
name, the elaborator emits a deprecation warning with a code action hint
to rename or delete the argument, and silently forwards the value to the
correct binder.
Supported forms:
- `@[deprecated_arg old new (since := "...")]` — renamed parameter,
warns and forwards
- `@[deprecated_arg old new "reason" (since := "...")]` — with custom
message
- `@[deprecated_arg removed (since := "...")]` — removed parameter,
errors with delete hint
- `@[deprecated_arg removed "reason" (since := "...")]` — removed with
custom message
A warning is emitted if `(since := "...")` is omitted.
When a parameter is deprecated without a replacement, the elaborator
treats it as no longer present: using it as a named argument produces an
error. Note that positional uses of deprecated arguments are not checked
— if a function's arity changed, the caller will simply get a "function
expected" error.
The `linter.deprecated.arg` option (default `true`) controls behavior:
when enabled, renamed args produce warnings and removed args produce
specific deprecation errors with code action hints; when disabled, both
fall through to the standard "invalid argument name" error. This lets
library authors phase out old parameter names without breaking
downstream code immediately.
Example (renamed parameter):
```lean
@[deprecated_arg old new (since := "2026-03-18")]
def f (new : Nat) : Nat := new
/--
warning: parameter `old` of `f` has been deprecated, use `new` instead
Hint: Rename this argument:
o̵l̵d̵n̲e̲w̲
---
info: f 42 : Nat
-/
#guard_msgs in
#check f (old := 42)
```
Example (removed parameter):
```lean
@[deprecated_arg removed (since := "2026-03-18")]
def g (x : Nat) : Nat := x
/--
error: parameter `removed` of `g` has been deprecated
Hint: Delete this argument:
(̵r̵e̵m̵o̵v̵e̵d̵ ̵:̵=̵ ̵4̵2̵)̵
-/
#guard_msgs in
#check g (removed := 42)
```
This PR re-enables `#print axioms` under the module system by computing
axiom dependencies at olean serialization time. It reverts #8174 and
replaces it with a proper fix.
Depends on #13142, which refactors `exportEntriesFnEx` to return all
three olean levels at once via a new `OLeanEntries` structure, allowing
extensions to share expensive computation.
The axiom extension uses `exportEntriesFnEx` to walk bodies of all
public declarations in the current module, collecting axiom dependencies
in a single batch with a shared cache across declarations. The results
are stored sorted for binary search and exported uniformly to all olean
levels. Downstream modules look up pre-computed axiom data from imported
oleans, so axiom collection never crosses module boundaries. During
elaboration of the current module, `collectAxioms` walks bodies directly
since they are always available locally.
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR adds `SymExtension`, a typed extensible state mechanism for
`SymM`,
following the same pattern as `Grind.SolverExtension`. Extensions are
registered at initialization time via `registerSymExtension` and provide
typed `getState`/`modifyState` accessors. Extension state persists
across
`simp` invocations within a `sym =>` block and is re-initialized on each
`SymM.run`.
This enables modules (e.g., the upcoming arithmetic normalizer) to
register persistent state without modifying `Sym.State` directly.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This PR adds a check that rejects Lake configurations where multiple
executables share the same root module name. Previously, Lake would
silently compile the root module once and link it into all executables,
producing identical binaries regardless of differing `srcDir` settings.
Lake (and Lean) rely on module names being unique within a package.
Rather than attempting to support duplicate module names, Lake now
produces a clear error at configuration load time, for both TOML and
Lean configuration files.
Closes#13013🤖 Prepared with Claude Code
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR adds named theorem sets for `Sym.simp` with associated
attributes, following the same pattern as `Meta.simp`'s
`register_simp_attr`.
- `register_sym_simp_attr my_set` creates a named set with its own
`PersistentEnvExtension` and attribute
- `@[my_set] theorem ...` adds a rewrite theorem
- `@[my_set] def ...` adds equation theorems from the definition
- `builtin_initialize symSimpExtension` registers a default
`@[sym_simp]` set
- `getSymSimpTheorems` / `getSymSimpExtension?` retrieve theorem sets at
tactic time
New files:
- `Sym/Simp/Attr.lean`: attribute logic (`mkSymSimpAttr`,
`registerSymSimpAttr`)
- `Sym/Simp/RegisterCommand.lean`: `register_sym_simp_attr` macro
Tests:
- `tests/pkg/sym_simp_attr/`: package test with user-defined set
(`my_sym_simp`)
- `tests/elab/sym_simp_set.lean`: tests for the builtin `@[sym_simp]`
set
This PR removes the obsolete `Lean.Environment.replay` from
`src/Lean/Replay.lean` and replaces it with the improved version from
`src/LeanChecker/Replay.lean`, which includes fixes for duplicate
theorem handling and Quot/Eq dependency ordering. The primed names
(`Replay'`, `replay'`) are renamed back to `Replay` and `replay`.
A test for the original issue (nested inductives failing with `replay`)
is added as `tests/elab/issue12819.lean`.
Closes#12819🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR fixes an issue where `realizeConst` would generate auxiliary
declarations
(like `_sparseCasesOn`) using the original defining module's private
name prefix
rather than the realizing module's prefix. When two modules
independently realized
the same imported constant, they produced identically-named auxiliary
declarations,
causing "environment already contains" errors on diamond import.
The fix re-privatizes the constant name under the current module before
passing it
to `withDeclNameForAuxNaming`, ensuring each realizing module generates
distinctly
named auxiliary declarations.
Fixes#12825
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR fixes some process signals that were incorrectly numbered.
From what I can tell, the code used signals and signal numbers for
Alpha/SPARC, not x86/ARM. The test was also broken and always green,
hiding the mistake.
The tests need to run with certain environment variables set that only
cmake really knows and that differ between stages. Cmake could just set
the variables directly when running the tests and benchmarks, but that
would leave no good way to manually run a single benchmark. So cmake
generates some stage-specific scripts instead that set the required
environment variables.
Previously, those scripts were sourced directly by the individual
`run_*` scripts, so the env scripts of different stages would overwrite
each other. This PR changes the setup so they can instead be generated
next to each other. This also simplifies the `run_*` scripts themselves
a bit, and makes `tests/bench/build` less of a hack.
This PR makes `@[cbv_opaque]` unconditionally block all evaluation of a
constant
by `cbv`, including `@[cbv_eval]` rewrite rules. Previously,
`@[cbv_eval]` could
bypass `@[cbv_opaque]`, and for bare constants (not applications),
`isOpaqueConst`
could fall through to `handleConst` which would unfold the definition
body.
The intended usage pattern is now: mark subterm-producing functions
(like
`DHashMap.insert`) as `@[cbv_opaque]` to prevent unfolding, and provide
`@[cbv_eval]` theorems on the *consuming* function (like
`DHashMap.contains`)
which pattern-matches against the opaque subterms.
This PR adds a warning to any `def` of class type that does not also
declare an appropriate reducibility.
The warning check runs after elaboration (checking the actual
reducibility status via `getReducibilityStatus`) rather than
syntactically checking modifiers before elaboration. This is necessary
to accommodate patterns like `@[to_additive (attr :=
implicit_reducible)]` in Mathlib, where the reducibility attribute is
applied during `.afterCompilation` by another attribute, and would be
missed by a purely syntactic check.
---------
Co-authored-by: Paul Reichert <6992158+datokrat@users.noreply.github.com>
Co-authored-by: Kim Morrison <kim@tqft.net>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR adds high priority to instances for `OfSemiring.Q` in the grind
ring envelope. When Mathlib is imported, instance synthesis for types
like `OfSemiring.Q Nat` becomes very expensive because the solver
explores many irrelevant paths before finding the correct instances. By
marking these instances as high priority and adding shortcut instances
for basic operations (`Add`, `Sub`, `Mul`, `Neg`, `OfNat`, `NatCast`,
`IntCast`, `HPow`), instance synthesis resolves quickly.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Kim Morrison <kim@tqft.net>
This PR sets up the new integrated test/bench suite. It then migrates
all benchmarks and some related tests to the new suite. There's also
some documentation and some linting.
For now, a lot of the old tests are left alone so this PR doesn't become
even larger than it already is. Eventually, all tests should be migrated
to the new suite though so there isn't a confusing mix of two systems.
This PR changes all `lean-toolchain` to use relative toolchain paths
instead of `lean4` and `lean4-stage0` identifiers, which removes the
need for manually linking toolchains via Elan.
After this PR, at least Elan 4.2.0 and 0.0.224 of the Lean VS Code
extension will be needed to edit core.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
This PR fixes two aspects of pretty printing of private names.
1. Name unresolution. Now private names are not special cased: the
private prefix is stripped off and the `_root_` prefix is added, then it
tries resolving all suffixes of the result. This is sufficient to handle
imported private names in the new module system. (Additionally,
unresolution takes macro scopes into account now.)
2. Delaboration. Inaccessible private names use a deterministic
algorithm to convert private prefixes into macro scopes. The effect is
that the same private name appearing in multiple times in the same
delaborated expression will now have the same `✝` suffix each time. It
used to use fresh macro scopes per occurrence.
Note: There is currently a small hack to support pretty printing in the
compiler's trace messages, which print constants that do not exist (e.g.
`obj`, `tobj`, and auxiliary definitions being compiled). Even though
these names are inaccessible (for the stronger reason that they don't
exist), we make sure that the pretty printer won't add macro scopes. It
also does some analysis of private names to see if the private names are
for the current module.
Closes#10771, closes#10772, and closes#10773
This PR ensures that failure in initial compilation marks the relevant
definitions as `noncomputable`, inside and outside `noncomputable
section`, so that follow-up errors/noncomputable markings are detected
in initial compilation as well instead of somewhere down the pipeline.
This may require additional `noncomputable` markers on definitions that
depend on definitions inside `noncomputable section` but accidentally
passed the new computability check.
Reported at
https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/Cryptic.20error.20message.20in.20new.20lean.20toolchain.3F.
This PR renames `instance_reducible` to `implicit_reducible` and adds a
new
`backward.isDefEq.implicitBump` option to prepare for treating all
implicit
arguments uniformly during definitional equality checking.
## Changes
**Rename `instance_reducible` → `implicit_reducible`:**
- Rename `ReducibilityStatus.instanceReducible` constructor to
`implicitReducible`
- Register new `[implicit_reducible]` attribute, keep
`[instance_reducible]` as alias
- Rename `isInstanceReducible` → `isImplicitReducible` (with deprecated
aliases)
- Update all references across src/ and tests/
The rename reflects that this reducibility level is used not just for
instances
but for any definition that needs unfolding during implicit argument
resolution
(e.g., `Nat.add`, `Array.size`).
**Add `backward.isDefEq.implicitBump` option:**
- When `true` (+ `respectTransparency`), bumps transparency to
`.instances` for
ALL implicit arguments in `isDefEqArgs`, not just instance-implicit ones
- Defaults to `false` for staging compatibility — will be flipped to
`true` after
stage0 update
- Adds `// update me!` to `stage0/src/stdlib_flags.h` to trigger CI
stage0 update
## Follow-up (after stage0 update)
- Flip `backward.isDefEq.implicitBump` default to `true`
- Fix resulting test/module failures
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR adds declaration names to leanchecker error messages to make
debugging easier when the kernel rejects a declaration.
Previously, leanchecker would only show the kernel error without
identifying which declaration failed:
```
uncaught exception: (kernel) type checker does not support loose bound variables
```
Now it includes the declaration name:
```
uncaught exception: while replaying declaration 'myDecl':
(kernel) type checker does not support loose bound variables
```
Fixes: #11937
---------
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: nomeata <148037+nomeata@users.noreply.github.com>
This PR adds the ability to register theorems with the `cbv_eval`
attribute in the reverse direction using the `←` modifier, mirroring the
existing `simp` attribute behavior. When `@[cbv_eval ←]` is used, the
equation `lhs = rhs` is inverted to `rhs = lhs`, allowing `cbv` to
rewrite occurrences of `rhs` to `lhs`.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
This PR sets the `irreducible` attribute before generating the equations
for recursive definitions. This prevents these equations to be marked as
`defeq`, which could lead to `simp` generation proofs that do not type
check at default transparency.
This issue is surfacing more easily since well-founded recursion on
`Nat` is implemented with a dedicated fix point operator (#7965). Before
that, `WellFounded.fix` was used, which is inherently not reducing, so
we did get the desired result even without the explicit reducibility
setting.
Fixes#12398.
This PR extends shake with tracking of attribute names passed to
`simp`/`grind`.
On the way there, it also fixes `register_simp/grind_attr` uses outside
`public meta section` as well as go-to-definition on declaration-level
uses of the created attributes (tactic-level goto would be a separate
todo).
This PR implements RFC #12216: native computation (`native_decide`,
`bv_decide`) is represented in the logic as one axiom per computation,
asserting the equality that was obtained from the native computation.
`#print axiom` will no longer show `Lean.trustCompiler`, but rather the
auto-generated names of these axioms (with, for example,
`._native.bv_decide.` in the name). See the RFC for more information.
This PR introduces a common MetaM helper (`nativeEqTrue`) used by
`native_decide` and `bv_decide` alike that runs the computation and then
asserts the result using an axiom.
It also deprecated the `ofReduceBool` axioms etc.
Not included in this PR is infrastructure for enumerating these axioms,
prettier `#print axioms` (should we want his) and tactic concurrency.
Fixes#12216.
This PR adds the new transparency setting `@[instance_reducible]`. We
used to check whether a declaration had `instance` reducibility by using
the `isInstance` predicate. However, this was not a robust solution
because:
- We have scoped instances, and `isInstance` returns `true` only if the
scope is active.
- We have auxiliary declarations used to construct instances manually,
such as:
```lean
def lt_wfRel : WellFoundedRelation Nat
```
`isInstance` also returns `false` for this kind of declaration.
In both cases, the declaration may be (or may have been) used to
construct an instance, but `isInstance`
returns `false`. Thus, we claim it is a mistake to check the
reducibility status using `isInstance`.
`isInstance` indicates whether a declaration is available for the type
class resolution mechanism,
not its transparency status.
**We are decoupling whether a declaration is available for type class
resolution from its transparency status.**
**Remak**: We need a update stage0 to complete this feature.
---------
Co-authored-by: Sebastian Ullrich <sebasti@nullri.ch>
This PR reverts #12000, which introduced a regression where `simp`
incorrectly rejects valid rewrites for perm lemmas.
The issue is that `NameGenerator.mkChild` creates names that don't
maintain the ordering assumption used by `acLt` for perm lemma
decisions. For example, after the change:
- Child generator creates names like `_uniq.102.2`
- Parent continues with `_uniq.7`
- But `Name.lt (.num (.num `_uniq 102) 2) (.num `_uniq 7)` is true
This causes fvars created later (in async tasks) to compare as smaller
than fvars created earlier, breaking the assumption that later fvars
compare greater according to `Name.lt`.
Fixes#12136.
🤖 Prepared with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This PR fixes an issue where go-to-definition would jump to the wrong
location in presence of async theorems.
While the elaborator does not explicitly depend on `FVar`s not being
reused between declarations, the language server turned out to do so. As
we would have to split the name generator in any case as soon as we add
any parallelism within proofs, we now do so for any async code in order
to uphold this invariant again.
---------
Co-authored-by: mhuisi <mhuisi@protonmail.com>
This PR makes the external checker lean4checker available as the
existing `leanchecker` binary already known to elan, allowing for
out-of-the-box access to it.
---------
Co-authored-by: Kim Morrison <kim@tqft.net>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This PR implements support for user-defined attributes at
`grind_pattern`. Suppose we have declared the `grind` attribute
```lean
register_grind_attr my_grind
```
Then, we can now write
```lean
opaque f : Nat → Nat
opaque g : Nat → Nat
axiom fg : g (f x) = x
grind_pattern [my_grind] fg => g (f x)
```
This PR implements user-defined `grind` attributes. They are useful for
users that want to implement tactics using the `grind` infrastructure
(e.g., `progress*` in Aeneas). New `grind` attributes are declared using
the command
```lean
register_grind_attr my_grind
```
The command is similar to `register_simp_attr`. After the new attribute
is declared. Recall that similar to `register_simp_attr`, the new
attribute cannot be used in the same file it is declared.
```lean
opaque f : Nat → Nat
opaque g : Nat → Nat
@[my_grind] theorem fax : f (f x) = f x := sorry
example theorem fax2 : f (f (f x)) = f x := by
fail_if_success grind
grind [my_grind]
```
TODO: remove leftovers after update stage0
This PR fixes an issue where `grind` fails when trying to unfold a
definition by pattern matching imported by `import all` (or from a
non-`module`).
Fixes#11715
---------
Co-authored-by: Sebastian Ullrich <sebasti@nullri.ch>
This PR fixes an issue where a `by` in the public scope could create an
auxiliary theorem for the proof whose type does not match the expected
type in the public scope.
Fixes#11672
This PR switches the way olean files store identifier suggestions. The
ordering introduced in #11367 and #11529 made sense if we were only
storing incorrect -> correct mappings, but for the reference manual we
want to store the correct -> incorrect mappings as well, and so it is
more sensible to store just the correct -> incorrect mapping that mimics
the author-generated data better.
Also tweaks error messages further in preparation for public-facing
@[suggest_for] annotations and forbids suggestions on non-public names.
Does not make generally-visible changes as there are no introduced uses
of @[suggest_for] annotations yet.
This PR adds a module resolution procedure to Lake to disambiguate
modules that are defined in multiple packages.
On an `import`, Lake will now check if multiple packages within the
workspace define the module. If so, it will verify that modules have
sufficiently similar definitions (i.e., artifacts with the same content
hashes). If not, Lake will report an error.
This verification is currently only done for direct imports. Transitive
imports are not checked for consistency. An overhaul of transitive
imports will come later.
This PR refines several error error messages, mostly involving invalid
use of field notation, generalized field notation, and numeric
projection. Provides a new error explanation for field notation.
## Error message changes
In general:
- Uses a slightly different convention for expression-type pairs, where
the expression is always given `indentExpr` and the type is given
`inlineExpr` treatment. This is something of a workaround for the fact
that the `Format` type is awkward for embedding possibly-linebreaking
expressions in not-linebreaking text, which may be a separate issue
worth addressing.
- Tries to give slightly more "why" reasoning — the environment does not
contain `String.parse`, and _therefore you can't project `.parse` from a
`String`_.
Some specific examples:
### No such projection function
```lean4
#check "".parse
```
before:
```
error: Invalid field `parse`: The environment does not contain `String.parse`
""
has type
String
```
after:
```
error: Invalid field `parse`: The environment does not contain `String.parse`, so it is not possible to project the field `parse` from an expression
""
of type `String`
```
### Type does not have the correct form
```lean4
example (x : α) := (foo x).foo
```
before:
```
error: Invalid field notation: Type is not of the form `C ...` where C is a constant
foo x
has type
α
```
after:
```
error: Invalid field notation: Field projection operates on types of the form `C ...` where C is a constant. The expression
foo x
has type `α` which does not have the necessary form.
```
## Refactoring
Includes some refactoring changes as well:
- factors out multiple uses of number (1, 2, 3, 212, 222) to ordinal
("first", "second", "third", "212th", "222nd") conversion into
Lean.Elab.ErrorUtils
- significant refactoring of `resolveLValAux` in `Lean.Elab.App` — in
place of five helper functions, a special-case function case analysis,
and a case analysis on the projection type and structure, there's now a
single case analysis on the projection type and structure. This allows
several error messages to be more explicit (there were a number of cases
where index projection was being described as field projection in an
error messages) and gave the opportunity to slightly improve positining
for several errors: field *notation* errors should appear on `foo.bar`,
but field *projection* errors should appear only on the `bar` part of
`foo.bar`.
This PR lets recursive functions defined by well-founded recursion use a
different `fix` function when the termination measure is of type `Nat`.
This fix-point operator use structural recursion on “fuel”, initialized
by the given measure, and is thus reasonable to reduce, e.g. in `by
decide` proofs.
Extra provisions are in place that the fixpoint operator only starts
reducing when the fuel is fully known, to prevent “accidential” defeqs
when the remaining fuel for the recursive calls match the initial fuel
for that recursive argument.
To opt-out, the idiom `termination_by (n,0)` can be used.
We still use `@[irreducible]` as the default for such recursive
definitions, to avoid unexpected `defeq` lemmas. Making these functions
`@[semireducible]` by default showed performance regressions in lean.
When the measure is of type `Nat`, the system will accept an explicit
`@[semireducible]` without the usual warning.
Fixes#5234. Fixes: #11181.
This PR improves the error message encountered in the case of a type
class instance resolution failure, and adds an error explanation that
discusses the common new-user case of binary operation overloading and
points to the `trace.Meta.synthInstance` option for advanced debugging.
## Example
```lean4
def f (x : String) := x + x
```
Before:
```
failed to synthesize
HAdd String String ?m.5
Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command.
```
After:
```
failed to synthesize instance of type class
HAdd String String ?m.5
Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command.
Error code: lean.failedToSynthesizeTypeclassInstance
[View explanation](https://lean-lang.org/doc/reference/latest/find/?domain=Manual.errorExplanation&name=lean.failedToSynthesizeTypeclassInstance)
```
The error message is changed in three important ways:
* Explains *what* failed to synthesize, using the "type class"
terminology that's more likely to be recognized than the "instance"
terminology
* Points to the `trace.Meta.synthInstance` option which is otherwise
nearly undiscoverable but is quite powerful (see also
leanprover/reference-manual#663 which is adding commentary on this
option)
* Gives an error explanation link (which won't actually work until the
next release after this is merged) which prioritizes the common-case
explanation of using the wrong binary operation
This PR prevents symbol clashes between (non-`@[export]`) definitions
from different Lean packages.
Previously, if two modules define a function with the same name and were
transitively imported (even privately) by some downstream module,
linking would fail due to a symbol clash. Similarly, if a user defined a
symbol with the same name as one in the `Lean` library, Lean would use
the core symbol even if one did not import `Lean`.
This is solved by changing Lean's name mangling algorithm to include an
optional package identifier. This identifier is provided by Lake via
`--setup` when building a module. This information is weaved through the
elaborator, interpreter, and compiler via a persistent environment
extension that associates modules with their package identifier.
With a package identifier, standard symbols have the form
`lp_<pkg-id>_<mangled-def>`. Without one, the old scheme is used (i.e.,
`l_<mangled-def>`). Module initializers are also prefixed with package
identifier (if any). For example, the initializer for a module `Foo` in
a package `test` is now `initialize_test_Foo` (instead of
`initialize_Foo`). Lake's default for native library names has also been
adjusted accordingly, so that libraries can still, by default, be used
as plugins. Thus, the default library name of the `lean_lib Foo` in
`package test` will now be `libtest_Foo`.
When using Lake to build the Lean core (i.e., `bootstrap = true`), no
package identifier will be used. Thus, definitions in user packages can
never have symbol clashes with core.
Closes#222.
