- VB: Report a warning about AssemblyKeyFile and AssemblyKeyName attributes being ignored by public signing.
- Disallow public signing for Net modules. The fact that the signing is public is not preserved in a module. The fact of signing is preserved by emitting attributes that are going to be ignored anyway if public signing is used.

Closes #11427.

Fixes #15910
Also fixes a sequence point issue with the let expression. Specifically, the source range for the query lambda included more than the expression of the let, but included the entire query clause. It now includes only the expression, like other query clauses.

* Combine deconstruction assignment and declaration, and support discards.

- Combine deconstruction assignment and declaration, and support discards.
- Add wildcards.work.md to track outstanding work.
- Bind each type syntax once in a deconstruction.
- Because tuples may contain declarations, adjust lambda disambiguation
  and adjust parsing of argument lists.
- Diagnose tuple element names on the left of a deconstruction.
- Add relational operators to disambiguating tokens in 7.5.4.2

* Disallow deconstruction declarations except at the statement level.
This is now a semantic restriction (until we decide to remove it).

* Revise logic to detect `var` in a declaration expression.
Plus other changes per code review.

* Add a test that GetTypeInfo on a discard expression doesn't crash.
* Small changes per code review.
* Add (skipped) test for var invocation in parens.
* Rename "Discarded" to "Discard"
* Changes recommended via code review.
* Minor changes to the handling of declaration expressions per code review.
* Addressing blocking feedback while Neal is OOF

Fixes https://github.com/dotnet/roslyn/issues/14794
Fixes https://github.com/dotnet/roslyn/issues/14832

Merging on behalf of @alrz

Fixes #14895

Also rephrases some existing error messages to incorporate local functions into
the description.

Fixes #13913.

If an IO error occurs while writing the doc comment stream we currently
let the exception rise out of the compiler. We should instead catch the
exception and surface a diagnostic.

* Fix crash on "is type" operator with typeless tuple expression.

Closes #13723
Fixes #13746 

* In a syntactic position where an lvalue is expected, we reserve `var (...)`
for possible future extension (e.g. a deconstruction), no matter what `...` is.
This specifically applies to
  - The left-hand-side of an assignment. The only syntactically valid form is as a deconstruction declaration statement; other forms are some kind of error. `var(1) = 2;`
  - Similarly for compound assignments, including ++ and --.
  - In any expression, following `out` or `ref`. These should not bind (successfully) as an invocation.
    - In an argument position, like `M(out var (1))`
    - In a "ref expression", for example `ref int x = ref var(1);` or `return ref var(1);`.

Fixes #13528.

Related to #12597.

Prevent future backward compatibility issues around supporting deconstruction declaration as an out argument.

Fixes #13148.

Fixes #13389

* tuples with names differing only by case are not allowed
* names that match predefined element names except for case do not result in additional names
* name-related errors are checked in case-insensitive fasion

Improve the grammar on a diagnostic.
Add further tests requested by reviewer.

Specifically
1. we will parse a predefined type where `var` is required.
2. we improve syntax recovery for a missing type - instead of treating the identifier as the type and a missing identifier, we report the type missing.
3. we restore the previous heuristic of checking for some type in the deconstruction to validate that it is a deconstruction.
Fixes #12803

Fixes #12900

* Implement source link feature

* Fix CommonCompiler to open source link stream, add E2E tests

* Reduce code duplication across VB and C#

  (e.g. ref local variable declaration)
We introduce a "ref expression" for use in expressions
  (e.g. right-hand-side of a ref variable initialization)
Also improve the diagnostic for local functions.
Fixes #12749, #12580