Fixes:#14600
Fixes:#11013
Fixes:#14116
Fixes:#16168

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=296550.

Variables declared within a ‘for’ condition are in scope only inside the condition, incrementors and body of the loop.
Variables declared within ‘for’ incrementors are in scope only inside the incrementors.

Related to #15630.

Also add wildcards.work.md to track outstanding work.

Rationalize behavior of GetSymbolInfo/GetTypeInfo/ClassifyConversion for DeclarationExpressionSyntax

Since DeclarationExpressionSyntax represents a declaration, all these APIs should return no information for it.

Fixes #13989.

* Implement pattern-matching in top-level scripts in which pattern variables become fields.
  Fixes #10603
* Move computation of better conversion from expression into `BetterConversionFromExpression`
* Update the out var specification to align with the implementation, and vice versa.

Fixes #13291.

Related to #12597.
Adjusted implementation of ExpressionEvaluator to handle new scoping rules. Some out and pattern variables become new EE variables.
Added unit-test for #13159.

wouldn't that be annoying to notice after we've shipped?

Similarly for TupleDeconstructionVariableDesignation.
Also found many places to handle both kinds of foreach statements.

Also update the out var syntax node to use the newly introduced
VariableComponent so it can be extended in the future to allow `out *`
or `out var (x, y)` etc without requiring any further changes to the
syntax model.
Fixes #12747, #12664, #12588, #1503

  (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

[Based on features/async-return with tests ported from that branch.]

- Feature flag.
- Syntax model changes.
- Parsing.
- Binding (for explicitly typed variables only).
- Flow analysis.
- SemanticModel – added new API GetDeclaredSymbol(ArgumentSyntax) to return symbol for the declared local.

Basic scenarios work end to end.

An ArrowExpressionClauseSyntax is special because it has an expression as its direct child. Because of that the binder was not correctly caching all nodes of the bound tree and instead was falling back to binding decendand nodes by themself when asked for them. This fails if in the decendant nodes there is a color color case.

With this change the binder does cache all of the ArrowExpressionClauseSyntax's children including the correctly resolved symbols for a color color situation.
Fixes #5362
Closes #8167

Related to #8817.

Related to #8817.

Related to #8817.

Related to #8817.

Related to #8817.

Also fix a bug in lowering of a switch statement where the target expression was not lowered.

Fixes #8815.
Related to #8817.

Fixes #9371
Related to #9284

Fixes #8810.
Related to #8816.

Fixes #9072 #9073 #9079 #9080

- Check for name conflicts for a local declared with [let <identifier> = …] statement.
- Create PatternVariableBinder for ReturnStatementSyntax.
- Create PatternVariableBinder for ThrowStatementSyntax.
- Create BlockBinder for a [let] statement used as an embedded statement.
- Add SemanticModel.GetDeclaredSymbol API for LetStatementSyntax.
- Test scope of pattern variable declared in [let], [return] and [throw] statements.

Related to # 8817.

Also add tests for scoping of variables declared within expression statements by using DeclarationPatternSyntax.

Related to #8817.