Possible optimization in interpolated string: inline interpolated constants

[gafter]

if an expression hole has a constant string value and no alignment or format, treat it as a literal instead of an expression. This would erase string.Format calls for scenarios like "throw new ArgumentException($"{nameof(argument)} should be something else".

Migrated from TFS/DevDiv 1097932

[AdamSpeight2008]

That should optimise down to just a string constant, not a Interpolation String.
NameOf( argument )
What about the case of multiple expression holes, one constant one not?
You can also extend it to any constant, not just strings. as well as including , alignment. As it is just padding the string with spaces. Since we are using constants, it could be worked out a compile-time.

Should this be more of an Analyser and Code-Fix? (Eg String-Format Diagnostics. Doesn't offer code-fixes yet))

[khellang]

@gafter Do you know if there's an existing issue on optimizing interpolated strings where you're basically just doing concatenation? (I couldn't find one)

So that var result = $"{a}{b}"; becomes var result = string.Concat(a, b); instead of var result = string.Format("{0}{1}", a, b);, at least for a certain amount of parameters.

See aspnet/HttpAbstractions#460 (comment) for reference.

[benaadams]

@khellang @gafter Additionally automatically calling .ToString() on valuetype params; currently:

public static string InterpolatedBox(int i)
{
    return $"? {i}";
}

boxes as

.method public hidebysig static string  InterpolatedBox(int32 i) cil managed
{
  // Code size       17 (0x11)
  .maxstack  8
  IL_0000:  ldstr      "\? {0}"
  IL_0005:  ldarg.0
  IL_0006:  box        [System.Runtime]System.Int32
  IL_000b:  call       string [System.Runtime]System.String::Format(string,
                                                                    object)
  IL_0010:  ret
} // end of method

vs adding ToString like

public static string InterpolatedToString(int i)
{
    return $"? {i.ToString()}";
}

which doesn't box

.method public hidebysig static string  InterpolatedToString(int32 i) cil managed
{
  // Code size       18 (0x12)
  .maxstack  8
  IL_0000:  ldstr      "\? {0}"
  IL_0005:  ldarga.s   i
  IL_0007:  call       instance string [System.Runtime]System.Int32::ToString()
  IL_000c:  call       string [System.Runtime]System.String::Format(string,
                                                                    object)
  IL_0011:  ret
} // end of method

As its known at compile time what is happening

[gafter]

@khellang I don't know if there is an issue for it.

[gafter]

See #6738 (comment) for why this is likely to never happen.