File-scoped namespace statements

[cgranade]

Suggestion

Allow namespace statements to end with a semicolon instead of a block, indicating that the namespace declaration applies to the entire file.

Considerations

Most Q# source files declare exactly one namespace, such that the extra level of indenting is unnecessary in most common cases. Allowing namespace declarations to be file-scoped would cut down on the amount of boilerplate and nesting, making Q# source files easier to read (esp. for newer users).

A similar discussion has led to the proposal and likely adoption of a similar feature into C# 10 (https://github.com/dotnet/csharplang/blob/main/proposals/csharp-10.0/file-scoped-namespaces.md).

Context

This proposal would not change any Q# semantics, but would provide a useful shorthand for existing features and semantics.

Examples

Example 1:
Using file-scoped namespaces to apply a namespace to all declarations in a file.

namespace Microsoft.Quantum.Foo;

// This function is declared with the fully
// qualified name Microsoft.Quantum.Foo.A.
function A() : String {
    return "aaaaaa";
}

Example 2: Mixing file- and block-scoped namespaces is forbidden.

namespace Microsoft.Quantum.Foo;

namespace Bar { // 💣: can't mix file- and block-scope namespace declarations.

}

Affidavit (please fill out)

Please add ticks by placing a cross in the box:

• [x] I have searched both open and closed suggestions and proposals on this site and believe this is not a duplicate.
• [x] I believe that the spirit of this suggestion is aligned with the design principles and general vision for Q#.

Please tick all that apply:

• [x] This is not a breaking change to the Q# language design
• [x] I or my organization would be willing to help implement and/or test this