Make generated code compile without implicit usings

[bernardnormier]

Fixes #4791.

The Slice generators emit fully qualified names for BCL types — except in two spots that relied on the consuming project enabling ImplicitUsings: the Span<byte> local emitted in every Request.Encode*/Response.Encode* helper, and the .Count() call emitted for tagged fixed-size collection fields. A consuming project without implicit usings — the SDK default — failed to compile the generated code.

Both emissions are now fully qualified, like everything else the generators emit: global::System.Span<byte>, and global::System.Linq.Enumerable.Count(...) in its static form — which also works when a cs::type attribute maps a sequence to an array, and drops a redundant nullable dereference by counting the non-null pattern variable.

To keep this from regressing, the Slice, Ice and Protobuf generator test projects (including the IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies projects) now build with <ImplicitUsings>disable</ImplicitUsings>, and their handwritten test files declare their usings explicitly. This also verifies that the slice2cs and protoc-gen-icerpc-csharp outputs compile without implicit usings — both already qualify all their references.

The new Sequence<int32>? and Dictionary<int32, int32>? tagged fields in TaggedTests.slice cover the previously untested fixed-size tagged collection encoding.

cs::type text is passed through verbatim: in a project that doesn't enable implicit usings, qualify the C# type names you write in cs::type — the test corpora now do (cs::type("global::System.Collections.Generic.List<bool>")).

The checked-in src/ZeroC.Slice.Symbols/Compiler files are deliberately not regenerated here: regenerating them is blocked by #4896.

What's Changed entry

The Slice compiler now generates code that compiles in projects that don't enable ImplicitUsings.

[Copilot]

Pull request overview

Updates generated Slice code to compile when consumers disable implicit usings.

Changes:

• Adds required framework namespaces to Slice generator preambles.
• Disables implicit usings across generator test projects and adds explicit test imports.
• Covers fixed-size tagged sequence and dictionary encoding.

Reviewed changes

Copilot reviewed 67 out of 67 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/ZeroC.Slice.Generator/Program.cs	Adds collection and LINQ preamble imports.
src/IceRpc.Slice.Generator/Program.cs	Adds required framework preamble imports.
tests/ZeroC.Slice.Generator.Tests/ZeroC.Slice.Generator.Tests.csproj	Disables implicit usings.
tests/ZeroC.Slice.Generator.Tests/WellKnownTypesTests.cs	Adds explicit framework imports.
tests/ZeroC.Slice.Generator.Tests/VariantEnumTests.cs	Adds explicit System import.
tests/ZeroC.Slice.Generator.Tests/TaggedTests.slice	Adds fixed-size tagged collections.
tests/ZeroC.Slice.Generator.Tests/TaggedTests.cs	Tests tagged collection encoding and decoding.
tests/ZeroC.Slice.Generator.Tests/StructTests.cs	Adds explicit LINQ import.
tests/ZeroC.Slice.Generator.Tests/SequenceDecodingTests.cs	Adds explicit IO import.
tests/ZeroC.Slice.Generator.Tests/EnumTests.cs	Adds explicit framework imports.
tests/ZeroC.Slice.Generator.Tests/DictionaryEncodingTests.cs	Adds explicit collection and LINQ imports.
tests/ZeroC.Slice.Generator.Tests/DictionaryDecodingTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/TypeNameQualificationTests.cs	Adds threading imports.
tests/IceRpc.Slice.Generator.Tests/StructTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/StreamTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/ServiceTests.cs	Adds threading imports.
tests/IceRpc.Slice.Generator.Tests/SequenceMappingTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/ProxyTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/OperationTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/OperationEncodingTests.cs	Adds task import.
tests/IceRpc.Slice.Generator.Tests/ModuleIdentifierTests.cs	Adds threading imports.
tests/IceRpc.Slice.Generator.Tests/InvokeOperationAsyncTests.cs	Adds IO and task imports.
tests/IceRpc.Slice.Generator.Tests/InvalidProxy.cs	Adds explicit System import.
tests/IceRpc.Slice.Generator.Tests/InterfaceTests.cs	Adds explicit System import.
tests/IceRpc.Slice.Generator.Tests/IdentifierAttributeTests.cs	Adds threading imports.
tests/IceRpc.Slice.Generator.Tests/IceRpc.Slice.Generator.Tests.csproj	Disables implicit usings.
tests/IceRpc.Slice.Generator.Tests/EnumTests.cs	Adds explicit System import.
tests/IceRpc.Slice.Generator.Tests/DictionaryMappingTests.cs	Adds explicit framework imports.
tests/IceRpc.Slice.Generator.Tests/CustomSequence.cs	Adds generic collections import.
tests/IceRpc.Slice.Generator.Tests/CustomDictionary.cs	Adds collection and LINQ imports.
tests/IceRpc.Protobuf.Tests/StreamTests.cs	Adds explicit framework imports.
tests/IceRpc.Protobuf.Tests/ServiceTests.cs	Adds explicit framework imports.
tests/IceRpc.Protobuf.Tests/PipeReaderExtensionsTests.cs	Adds explicit framework imports.
tests/IceRpc.Protobuf.Tests/OperationTests.cs	Adds explicit framework imports.
tests/IceRpc.Protobuf.Tests/IceRpc.Protobuf.Tests.csproj	Disables implicit usings.
tests/IceRpc.Protobuf.Tests/AsyncStreamTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/TypeNameQualificationTests.cs	Adds threading imports.
tests/IceRpc.Ice.Generator.Tests/StructTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/ServiceTests.cs	Adds threading imports.
tests/IceRpc.Ice.Generator.Tests/SequenceMappingTests.cs	Adds collection and task imports.
tests/IceRpc.Ice.Generator.Tests/ProxyTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/OperationTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/InvokeOperationAsyncTests.cs	Adds IO and task imports.
tests/IceRpc.Ice.Generator.Tests/InvalidProxy.cs	Adds explicit System import.
tests/IceRpc.Ice.Generator.Tests/InterfaceTests.cs	Adds explicit System import.
tests/IceRpc.Ice.Generator.Tests/IdentifierAttributeTests.cs	Adds threading imports.
tests/IceRpc.Ice.Generator.Tests/IceRpc.Ice.Generator.Tests.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Tests/ExceptionTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/DictionaryMappingTests.cs	Adds collection and task imports.
tests/IceRpc.Ice.Generator.Tests/CustomSequence.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Tests/CsIdentifierOnModuleTests.cs	Adds threading imports.
tests/IceRpc.Ice.Generator.Tests/ClassTests.cs	Adds explicit System import.
tests/IceRpc.Ice.Generator.Base.Tests/TypeIdAttributeTests.cs	Adds explicit System import.
tests/IceRpc.Ice.Generator.Base.Tests/TaggedTests.cs	Adds generic collections import.
tests/IceRpc.Ice.Generator.Base.Tests/SlicingTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Base.Tests/SequenceMappingTests.cs	Adds generic collections import.
tests/IceRpc.Ice.Generator.Base.Tests/SequenceDecodingTests.cs	Adds explicit IO import.
tests/IceRpc.Ice.Generator.Base.Tests/IceRpc.Ice.Generator.Base.Tests.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Base.Tests/EnumTests.cs	Adds explicit System import.
tests/IceRpc.Ice.Generator.Base.Tests/CustomSequence.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Base.Tests/ClassTests.cs	Adds explicit IO import.
tests/IceRpc.Ice.Generator.Base.Tests/ActivatorTests.cs	Adds explicit framework imports.
tests/IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies/DPrime/DPrime.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies/D/D.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies/C/C.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies/B/B.csproj	Disables implicit usings.
tests/IceRpc.Ice.Generator.Base.Tests.ReferencedAssemblies/A/A.csproj	Disables implicit usings.

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[InsertCreativityHere]

I think all the changes to the tests are awesome and good and we should keep them. But I'm not sure about the changes to the 2 generators. Our original philosophy was to always qualify our own type-emissions, instead of injecting usings, and it's clear that in 2 places, we weren't careful enough.

That philosophy isn't set in stone of course, but this PR seems like a weak reason to deviate. The bugs in question could be fixed by just slightly tweaking 2 lines of code in our generators, with 0 side-effects to any users.

Adding 2 or 3 new usings to every generated file (possibly breaking some user's Slice in a patch release)... it just feels like a worse solution to the problem here.

[InsertCreativityHere]

This PR claims that we emit unqualified collection types, but as far as I can tell, that's simply incorrect. Every IList, Dictionary, IEnumerable, etc. that we emit, is always fully qualified. Adding this using doesn't fix any bug.

I do see a use-case in making the cs::type attribute slightly more ergonomic.
I'm not completely against that, but I definitely think it should be in a different PR, since "making cs::type more friendly" is a completely unrelated to the implicit-usings.

[bernardnormier]

You're right — I checked: the generated corpora contain 541 fully qualified System.Collections.Generic references and zero unqualified generator-emitted collection types. The PR now takes the direction your comment points to: no preamble usings at all. The two emissions that relied on implicit usings are now fully qualified like everything else (global::System.Span, and global::System.Linq.Enumerable.Count(...) in its static form), and the corpora's cs::type texts qualify their collection types since those projects now disable implicit usings — with implicit usings enabled, cs::type("List") keeps working as before.

[Copilot]

Pull request overview

Copilot reviewed 69 out of 69 changed files in this pull request and generated no new comments.

[externl]

Looks good.

[InsertCreativityHere]

Looks good to me!