fix precompiling packages specifically (#4014)

Author: IanButterworth

src/REPLMode/command_declarations.jl

@@ -384,6 +384,7 @@ Create a minimal project called `pkgname` in the current folder. For more featur
 ],
 PSA[:name => "precompile",
     :api => API.precompile,
+    :should_splat => false,
     :arg_count => 0 => Inf,
     :completions => :complete_installed_packages,
     :description => "precompile all the project dependencies",

test/new.jl

@@ -2229,19 +2229,17 @@ end
 
         api, arg, opts = first(Pkg.pkg"precompile Foo")
         @test api == Pkg.precompile
-        @test arg == "Foo"
+        @test arg == ["Foo"]
         @test isempty(opts)
 
-        api, arg1, arg2, opts = first(Pkg.pkg"precompile Foo Bar")
+        api, arg, opts = first(Pkg.pkg"precompile Foo Bar")
         @test api == Pkg.precompile
-        @test arg1 == "Foo"
-        @test arg2 == "Bar"
+        @test arg == ["Foo", "Bar"]
         @test isempty(opts)
 
-        api, arg1, arg2, opts = first(Pkg.pkg"precompile Foo, Bar")
+        api, arg, opts = first(Pkg.pkg"precompile Foo, Bar")
         @test api == Pkg.precompile
-        @test arg1 == "Foo"
-        @test arg2 == "Bar"
+        @test arg == ["Foo", "Bar"]
         @test isempty(opts)
     end
 end