When string concatenation encounters non-strings (e.g. path + '/', name + someInt32, etc.), it calls overloads of String.Concat that accept objects. These overloads then just call ToString on each of the objects, mapping to the C# spec which states that "any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object." When any of the individual items being concatenated is a value type, that object first gets boxed to be passed to String.Concat as an object, only to then have ToString called on the boxed object.

This commit changes the local rewriter for string concatenation to test whether an argument is of an appropriate type, and if it is, to call ToString on it directly, rather than first boxing it. This can then affect which overload of Concat is used, as the type of the argument has changed to be String. The primary benefit of this is saving the allocation per value-type item. There are some secondary benefits, as well; for example, as there is a four-string overload of Concat but no four-object overload of Concat, if this optimization is able to force all of the items to be strings, the four-string overload can be used rather than allocating an object array for the inputs and then another string array for the resulting strings (inside of Concat).

This commit also includes an additional optimization specific to const chars; rather than doing a ToString call at run time, we can do it at compile-time and emit a literal string instead of a literal char, saving both the boxing and the string allocation at run time.

Add skipped test for #399

Add test for string concatenation operator with mutable value types

NuGet authoring for Microsoft.DiaSymReader

VB: Remove unnecessary check for ModuleBuilderOpt during lowering phase

Exclude mscorlib from Emit test conflict checking

In the emit tests we currently check every module to see if we're
emitting an assembly with a name we've already seen. PeVerify
requires that we create a new AppDomain for every conflict we find.
However, mscorlib will always produce a conflict, so this ignores
mscorlib when checking for a conflict and doesn't create a new
AppDomain if it is found during emit.

Use AssertTheseEmitDiagnostics instead of compilation.VerifyEmitDiagnostics to keep the orignal baseline form.

do not load all diagnostic analyzers in host analyzer references

we can end up load analyzers for a language that does not even exist in current solution.

properly handle VB Global namespace in DeclaredSymbolInfo

Add *.wrn to .gitignore

Add skipped test for https://github.com/dotnet/roslyn/issues/320

Fix SimpleDiagnostic GetHashCode is more specific than Equals

These checks were required for some VB tests, not for product code.
By updating VB tests, we can remove them and simplify the lowering phase.

Add skipped test for https://github.com/dotnet/roslyn/issues/320: Possible bug in Batch Fixer merge algorithm.

Create new projects for System.Runtime.Analyzers

fix #314 - remove dead code

It is apparently possible for a test to exit with an error code, produce
no HTML file and no output.  In that case the call to Aggregate was
failing with an exception.  Change it to use ToArray +
File.WriteAllLines.

This won't fix the underlying problem but will at least identify the
test that is failing.

Substitute generic type arguments for generic frames in the Call Stack Window.

removed dead code. code I wrote long time ago for specific indenter case is left in code base when it is no longer needed.

This change also ensures that we get non-fatal Watson reports when we're in the continuation of a call to get generic type arguments or argument values from the debugee process.

Fixes #309 (Incremental build fix)

Fix #295

Review feedback from Jason

Program for running tests in parallel

These suites are failing on a number of machines without this change.
Disabling.