Better error messages for malformed packages

src/Squirrel/Internal/EnumerableExtensions.cs

@@ -12,6 +12,30 @@ public static IEnumerable<T> Return<T>(T value)
             yield return value;
         }
 
+        /// <summary>
+        /// Essentially just .Single() but with context aware error messages which are more helpful to a user.
+        /// Eg. "Invalid {is}. Only a single {what} expected in {in}."
+        /// </summary>
+        public static T ContextualSingle<T>(this IEnumerable<T> source, string strIs, string strWhat, string strIn = null)
+        {
+            var c = System.Linq.Enumerable.Count(source);
+            if (c == 0) {
+                throw new InvalidOperationException(
+                    $"Invalid {strIs}: One {strWhat} expected" +
+                    (strIn == null ? "." : $" in {strIn}.") +
+                    " None was found.");
+            }
+
+            if (c > 1) {
+                throw new InvalidOperationException(
+                    $"Invalid {strIs}: Only a single {strWhat} expected" +
+                    (strIn == null ? "." : $" in {strIn}.") +
+                    $" Actually found: {c}.");
+            }
+
+            return System.Linq.Enumerable.First(source);
+        }
+
         /// <summary>
         /// Enumerates the sequence and invokes the given action for each value in the sequence.
         /// </summary>

src/SquirrelCli/Program.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
@@ -190,12 +190,15 @@ static void Releasify(ReleasifyOptions options)
             }
 
             foreach (var file in toProcess) {
-                Log.Info("Creating release package: " + file.FullName);
+                Log.Info("Creating release for package: " + file.FullName);
 
                 var rp = new ReleasePackage(file.FullName);
                 rp.CreateReleasePackage(Path.Combine(di.FullName, rp.SuggestedReleaseFileName), contentsPostProcessHook: (pkgPath, zpkg) => {
-                    var nuspecPath = Directory.GetFiles(pkgPath, "*.nuspec", SearchOption.TopDirectoryOnly).First();
-                    var libDir = Directory.GetDirectories(Path.Combine(pkgPath, "lib")).First();
+                    var nuspecPath = Directory.GetFiles(pkgPath, "*.nuspec", SearchOption.TopDirectoryOnly)
+                        .ContextualSingle("package", "*.nuspec", "top level directory");
+                    var libDir = Directory.GetDirectories(Path.Combine(pkgPath, "lib"))
+                        .ContextualSingle("package", "'lib' folder");
+
                     var awareExes = SquirrelAwareExecutableDetector.GetAllSquirrelAwareApps(libDir);
 
                     // unless the validation has been disabled, do not allow the creation of packages without a SquirrelAwareApp inside
@@ -224,10 +227,10 @@ static void Releasify(ReleasifyOptions options)
                     // often supports x86 emulation, so we want to pick the least compatible architecture
                     // for the package.
                     var archOrder = new[] { /*RuntimeCpu.Arm64,*/ RuntimeCpu.X64, RuntimeCpu.X86 };
-                    var pkgarch = archOrder.First(o => pearchs.Contains(o));
+                    var pkgarch = archOrder.FirstOrDefault(o => pearchs.Contains(o));
 
                     if (pkgarch == RuntimeCpu.Unknown) {
-                        Log.Warn("Unable to detect package machine architecture. Are the SquirrelAware binaries compatible?");
+                        Log.Warn("Unable to detect package machine architecture from SquirrelAware binaries.");
                     } else {
                         Log.Info($"Package architecture: {pkgarch} (implicit, from a SquirrelAware binary)");
                     }