Use #if with ! not operator and symbols for the 'Applies to' table rows consistenly

[StipoR]

Describe the bug

When I want to test my shared project (.shproj) in my .NET Core 3.1 test project, I must also explicitly include .NET Standard 2.0 symbols (NETSTANDARD; NETSTANDARD2_0; NETSTANDARD2_0_OR_GREATER; NETSTANDARD1_6_OR_GREATER; NETSTANDARD1_5_OR_GREATER; NETSTANDARD1_4_OR_GREATER; NETSTANDARD1_3_OR_GREATER; NETSTANDARD1_2_OR_GREATER; NETSTANDARD1_1_OR_GREATER; NETSTANDARD1_0_OR_GREATER) in my test project because this shared project is part of a larger class library that targets also .NET Standard 2.0 and the code depends on these symbols being defined. This causes a build of my .NET Core 3.1 test project to fail with the following errors:

1>C:\Users\Stipo.nuget\packages\polyfill\7.5.0\contentFiles\cs\netstandard2.0\Polyfill\StringPolyfill.cs(23,16,23,20): error CS0121: The call is ambiguous between the following methods or properties: 'string.Join(char, params string?[])' and 'string.Join(string?, params string?[])'
1>C:\Users\Stipo.nuget\packages\polyfill\7.5.0\contentFiles\cs\netstandard2.0\Polyfill\StringPolyfill.cs(34,16,34,20): error CS0121: The call is ambiguous between the following methods or properties: 'string.Join(char, params object?[])' and 'string.Join(string?, params object?[])'
1>C:\Users\Stipo.nuget\packages\polyfill\7.5.0\contentFiles\cs\netstandard2.0\Polyfill\StringPolyfill.cs(45,16,45,20): error CS0121: The call is ambiguous between the following methods or properties: 'string.Join(char, string?[], int, int)' and 'string.Join(string?, string?[], int, int)'
1>C:\Users\Stipo.nuget\packages\polyfill\7.5.0\contentFiles\cs\netstandard2.0\Polyfill\StringPolyfill.cs(56,16,56,20): error CS0121: The call is ambiguous between the following methods or properties: 'string.Join(char, IEnumerable)' and 'string.Join(string?, IEnumerable)'

because .NET Core 3.1 has string.Join overloads with both string and char separator parameter.

One solution would be to use new string([separator]) instead of new([separator]) in the StringPolyfill.cs.

But the better solution would be to use the #if with the ! not operator and with the list of symbols for the 'Applies to' table rows consistently in the entire Polyfill source code.

So, #if NETSTANDARD2_0 || NETFRAMEWORK in the StringPolyfill.cs would be replaced
with #if !(NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER) because the 'Applies to' table of the string.Join(Char, String[]) method has the following rows:

.NET | Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard | 2.1

Another example is public static bool Contains(this string target, char value) from the Polyfill_String.cs.
Instead of #if NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0
use #if !(NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER) because the 'Applies to' table of the string.Contains(Char) method has the following rows:

.NET | Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Standard | 2.1

Using this approach consistently in the entire Polyfill source code aligns it better with the .NET documentation.

Minimal Repro

Extract the PolyfillSolution.zip and try building the MySharedProjectTest project.

[SimonCropp]

i though shproj were basically abandonware?

[StipoR]

Shproj are still supported but they don't get much love since since the same thing can be done with globbing.

But that is irrelevant. We have a shared code that our class library imports and we have a test project that also imports and tests that shared code. Class library also targets .NET Standard 2.0 so we have NETSTANDARD* symbols in that shared code. In our test project we test the behavior of the .NET Standard shared code by targeting .NET Core 3.1. Since NETSTANDARD* symbols are not automatically defined in the test project we define them explicitly and that breaks the build of the Polyfill code since both NETSTANDARD* and NETCOREAPP* symbols are defined.

If the ! not operator and symbols for the 'Applies to' table rows would be used consistenly in the Polyfill source code, the problem would not occur.