so that there will be no conflict if they are used as netmodules
Fixes #1228

These are failing in certain build configurations.

This change takes the following steps:

- Changes EmitStreamProvider to wrap a single Stream instead of a group
of Stream.
- Changes the emit behavior to consider Analyzer errors before
attempting to write the PE / PDB Stream to disk.

Been almost a month since the code formatter was run so this change was
a bit larger than would be expected for a normal (weekly) update.  Diffs
mostly around:

- Whitespace changes
- Missing copyright headers
- Missing visibility modifiers

Fixes a crash while generating debug information for a compilation with two metadata references that represent the same assembly, first with no aliases and second with an alias.   (changeset 1412130)

Makes it easier to use the property and fixes a couple of bugs, where the code didn't check for either IsDefault or IsEmpty. Now all use-sites just need to check for IsEmpty.

Fixes 1119812. (changeset 1410494)

Changes:

To enable producing both Portable and native PDB formats we need to move the format specific imports encoding down to the PdbWriter. Instead of constructing NamespaceScope objects containing strings that encode usings/imports the C# and VB constructs that hold on to bound imports (ImportChain in C#, SourceFile in VB) now implement a new CCI-level interface IImportScope that provides an array of UsedTypeOrNamespace for each import scope. UsedTypeOrNamespace struct now doesn’t contain strings but symbols that represent the entities that re referenced in usings/Imports. IImportScope only represents imports on file level and below. Project level imports are exposed via new API on Cci.IModule (GetImports method). To represent a namespace a new CCI-level interface INamespace is introduced and implemented by NamespaceSymbol. In future we could replace usage of qualified namespace strings with this interface in other places in the compiler-CCI interface, but to minimize the impact I have not done so in this change.

Background:

Currently C# and VB compilers build a list of namespace scopes in NamespaceScopeBuilder that are then passed via MethodBody to the MetadataWriter, which then passes them to the PdbWriter. The NamespaceScopeBuilder encodes various forms of usings, extern aliases and imports in specially formatted strings that the EE understands how to decode. It constructs a list of all usings/imports/extern-aliases/etc. for each method. The PdbWriter then writes these string lists to PDB namespace scope records and implements a forwarding optimization – within a set of methods that have the same usings we designate one that we associate the strings with and the others forward to it. The forwarding is implemented differently by VB and C#. VB also defines some additional namespace scope records for default namespace, NoPia assembly names and method namespace.

The new portable PDB format has a different, simpler and more efficient representation of import scopes with the same encoding for C# and VB. Import scopes are first class entities that have parent pointer and thus form a tree. The structure of the tree is language specific. The root of the tree represents a project/compilation-wide import scope. For C# this scope contains assembly reference aliases (/r:Alias=Reference.dll). For VB this scope declares project level imports. The import scope tree for VB is 2 level deep – file level and project level. C# may define deeper trees as namespaces may define their own usings.
Also some information that Dev12 encodes in PDB namespace scopes is not used anymore by our new EEs (such as VB NoPia names, VB method namespace). These are not emitted to Portable PDB since the old EEs won’t be able to consume the new format anyways.
 (changeset 1410225)

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)

1) Change MethdCompiler.BindMethodBody to associate correct syntax with BoundBlocks it creates when binding constructor with constructor initializer call (two bound blocks are created – outer one defines a closure scope for constructor parameters, the inner one defines a closure scope for variables in the body).
2) Introduce MethodDebugId – a method ordinal and generation ordinal pair
3) Introduce LamdbaDebugInfo and ClosureDebugInfo to represent information (syntax offset) we use to figure out how to map lambdas and closures to the previous generation.
4) Adds a new PDB CDI record (#7) to store lambda and closure debug info.
5) Generalizes CalculateLocalSyntaxOffset to handle positions in field/property initializers and constructor initializers. Use it to calculate syntax offsets of lambdas and closure scopes. (TODO: rename CalculateLocalSyntaxOffset to CalculateSyntaxOffset).
6) Replace lambda and scope ordinal dispenser integers with array builders that collect LambdaDebugInfo and ClosureDebugInfo.
7) Use TryGet- pattern for all VariableSlotAllocator APIs.
8) Implements mapping of lambda method and display class names to previous generation via VariableSlotAllocator.
 (changeset 1407240)

If an assembly has "global" alias don't qualify namespace name in PDB with an extern alias. (changeset 1407218)

The compiler emits catch-all handler to all async methods. In case of async void methods we also emit the offset of the catch handler to PDB, so that the debugger can pretend that exceptions thrown by the async method are unhandled. Otherwise they are lost. Currently the compiler emits wrong offset, so the debugger is completely confused and displays "no source location" when such exception occurs.

     The fix is to remove a synthesized "nop" instruction that was incorrectly used to track the catch handler IL offset. Instead mark the synthesized BoundCatchHandler node by a flag and create the IL marker in the CodeGen when emitting instructions for such bound node.

     Affects both C# and VB.

     Fixes bug 1114809. (changeset 1405564)

Changes the 4.0+ lock statement IL pattern to improve debugging experience and to match VB compiler. Previously “restarting” the lock by dragging IP to the lock() statement header didn’t reset “lockTaken” flag and Monitor.Enter threw an exception.
Fixes bug 767299.
 (changeset 1403711)

Assembly-qualified names in custom debug info should be produced using the same code path as assembly-qualified names in emitted code.  This fixes an unhandled case (pointers as type arguments).

This also brings us closer to the native behavior: we had started emitting the assembly name for types in the current assembly, which the native compiler did not.

CR: alekseyt; tomat (changeset 1397706)