The error message doesn’t make sense when installing a ‘Packages.config’ format package which does not meet the existing package source mappings

[v-luzh]

NuGet Product Used

Visual Studio Package Management UI

Product Version

VS Main/11316.25 + NuGet Client Dev/7.3.0.45

Worked before?

It is not a regression.

Impact

It bothers me. A fix would be nice

Repro Steps & Context

Notes:

1. Repro rate: 100%.

Repro Steps:

1. Create a C# Console App (.NET Framework) in VS and click the menu ‘Tools->Options->NuGet Package Manager->Package Source Mapping’.
2. Add a package pattern ‘Microsoft.*’ with source ‘nuget.org’ and open the project-level PM UI.
3. Click the ‘Browse’ tab and select ‘nuget.org’ in the ‘Package source’ dropdown list.
4. Search for the package ‘EntityFramework’, select the searched package in the package list and click ‘Install’ button.
5. Select ‘Packages.config’ format and click OK button.

Expected Result:

The error message should make sense. It should tell user the package doesn't meet the existing package source mapping.

Actual Result:

The error message doesn’t make sense as the screenshot below. The package can be found in the source actually.

[martinrrm]

The error message is not clear, we should update it