* Add reproducer for #34872

* Fix bug and add test

* WIP

* Test similar scenario in VB

* Add void check in ClassifyConversionFromType, update tuple tests

* Cleanup

* Don't emit readonly attributes on members within readonly structs

* Check ContainingType.IsReadOnly before EnsureIsReadOnlyAttributeExists just for consistency

* Symbol display for readonly members

* Add coverage

* Test malformed properties and events

* Show readonly keyword on non-field members in QuickInfo

* Use IsDeclaredReadOnly for symbol display (WIP)

* Update based on design and fix some test failures

* Add readonly keywords to various IL tests

* Fix more tests, respond to feedback

* Fix compile error

* Don't display readonly keyword for implicit readonly getters from source

* Don't show readonly keyword for members contained within a readonly struct

* Move from extension methods to private statics

* Nullable Deconstruction in foreach loops:
- Visit deconstruction in foreach loops, rather than handling it directly
- Add tests

Implements a design change where overrides are allowed to change the
type of the member as long as there is an implicit nullable reference
conversion from the overriding type to the overridden type according to
the nullable variance rules.

Fixes #23268
Fixes #30958

Related to #32054.

Closes #28834.
Closes #30061.

- Allow ```base(object)``` in interfaces
- System.Object members should be available of off ```base(<some interface type>)```.

Ensure unimplemented interface members are reported even in presence of unification warnings (#35422)

* Remove RoslynProjectType

* Remove ToolsVersion, namespace from Project tags

* Remove updating of MSBuildAllProjects

* Update BuildBoss

* Delete DeployTooolsetCompiler

(cherry picked from commit c421f124)

* Permit stackalloc in nested contexts. (#28969)
Fixes #26759

Fixes #29956

Also introduce a helper `TypeSymbol.IsVoidType()`

* Additional Nullability checks for deconstruction:
- Check 'this' param for extension deconstruct
- Re-infer the argument types for generic extension deconstruct
- Update the deconstruction method in instance cases
- Update return type with visited arguments
- Update tests

Fixes #35278

Fixes #34018

Also fixes a corresponding issue in the switch expression
Fixes #34299
See also #35029

Fixes #30069

Fixes #30939

Make sure nullability mismatch in constraints specified in different partial declarations (types/methods) are properly detected and reported. (#35272)

 Make sure nullability mismatch in constraints specified in different partial declarations (types/methods) are properly detected and reported.

Fixes #30229.
Fixes #35179.

Implements the following LDM decision:

For partial types, the invariant matching from type inference and merging. A mismatch
between two non-oblivious candidates produces an error. No warnings are produced.

For partial methods, nullability has to match with exception for oblivious and we produce warnings.
For the result, we use the implementation signature inside the implementation, and the
declaration signature for the callers.

This makes 2 changes:
1. Reinfer the GetEnumerator method based on nullable analysis of the
foreach expression type.
2. Use that information to update the collection element type based on
that same analysis.

* Make Generated syntax trees restore to project nullability

Fixes #29894

A reference to an unconstrained type parameter in nullable-disabled code should be treated as *oblivious*, and therefore reading them should be considered to produce non-null values, and we are permitted to assign null values to them without a diagnostic.
Fixes #34842

Also disable the old WRN_DotOnDefault when the nullable feature is enabled.
Fixes #34855

When we relaxed the requirement for pattern matching open types to a
constant pattern to not require a conversion from the pattern expression
to the open type, but the pattern expression should be required to have
a constant value.

Fixes #34980

* Implement MetadataAsSource for ref and readonly structs

* MetadataAsSource for readonly members

* Fix NotImplementedException errors. Fix some ArrayBuilder leaks.

* Fix a leak. Fix implicit readonly attribute test.

* List passed to GetUpdatedDeclarationAccessibilityModifiers needs to support Remove

* Allow specifying a metadata language version for MetadataAsSourceTests

* Remove unused SyntaxTokenList members. Comment readonly event generation.

* Check VB MetadataAsSource for readonly members

* Fixes from feedback

* Add test for not implicitly readonly struct getter

* Label arguments in call to GetCustomAttributesForToken

* Reference issue about readonly event public API

The current implementation of closure conversion creates closure environments for each
new scope. This change tries to minimize the number of closure environments, and thus
closure environment allocations, when possible by merging "adjacent" closure environments.

To merge two closure environments, they have to:

1. Be captured by exactly the same set of closures
2. Have no backwards branching between the allocation of the two environments
3. Have the same environment lifetime

If so, all of the variables will be merged into a single closure environment. 

Fixes #29965

* Only emit readonly attributes implicitly when readonly members feature is enabled

* Comment about reasoning and use Theory for test

Related to #28834.

Also, remove obsolete comments from a test. Closes #30003.