[fpellet]

Closes #4485

Since #4457, paket install no longer warns about missing redirects: force for FSharp.Core in a project that declares net10.0, but it still warned for an SDK project that takes its framework from Directory.Build.props, a common way to set the framework of every project in one place. Binding redirects don't apply to such a project, so the warning was a false positive.

Cause

Paket only reads the properties of the project file: it doesn't read Directory.Build.props.

• A project that inherits its framework declares none, and ProjectFile.getTargetProfiles falls back to net40, which shouldWarnAboutFSharpCoreRedirects (InstallProcess.fs) takes for .NET Framework.
• A TargetFramework set to a property defined there, as $(DefaultTargetFramework), expands to an empty string, which FrameworkDetection reads as net10, .NET Framework 1.0. The same goes for an empty entry of TargetFrameworks, as in net8.0; .

Fix

• ProjectFile.getDeclaredTargetProfiles (GetDeclaredTargetProfiles()) returns the profiles that the project file declares, without the net40 fallback. getTargetProfiles is defined on top of it and keeps the fallback.
• Empty framework values are ignored, so such a project declares no framework. Where Paket needs the framework of the project, as for framework: auto-detect, paket pack or binding redirects, it falls back to net40 like for a project without framework, instead of net10.
• The warning checks the declared profiles: when the project file declares none, Paket can't tell and doesn't warn.

As suggested in the issue, Paket keeps reading the XML of the project only, since evaluating each project with MSBuild costs about 0.8 s. A project that inherits net48 from Directory.Build.props is therefore no longer warned, and one with net$(Version) still is, as before.

Tests

• TargetFrameworkSpecs: the declared profiles of an SDK project without framework (none, while GetTargetProfiles keeps net40), with $(DefaultTargetFramework), with net8.0; and with net48.
• BindingRedirect: the i004485-fsharp-core-warning-inherited-framework scenario has a project that inherits its framework from Directory.Build.props, one that sets it through a property defined there, and one that declares net48. paket install warns about the net48 project only; without the fix, it warned about all three.