Emit a warning when SemVer 2.0 format version is used with explicit SemVer 1.0

Should the user explicitly set `nugetPackageVersion.semVer` to `1` but
use a SemVer 2 prerelease in their `version` (such as: `1.0.0-preview.{height})
a warning will now be displayed telling the user they are probably not
getting what they expected.

Fixes #318

Author: robmen

src/NerdBank.GitVersioning/VersionOracle.cs

@@ -385,6 +385,22 @@ public IDictionary<string, string> CloudBuildVersionVars
         /// </summary>
         public int SemVer1NumericIdentifierPadding => this.VersionOptions?.SemVer1NumericIdentifierPaddingOrDefault ?? 4;
 
+        /// <summary>
+        /// Gets the SemVer 1 format without padding or the build metadata.
+        /// </summary>
+        public string SemVer1WithoutPaddingOrBuildMetadata =>
+            $"{this.Version.ToStringSafe(3)}{MakePrereleaseSemVer1Compliant(this.PrereleaseVersion, 0)}";
+
+        /// <summary>
+        /// Determines if it was likely the user misconfigured their the prerelease version options and
+        /// their semver setting.
+        /// </summary>
+        /// <returns>False when NuGet SemVer 1 explicitly set but the prerelease does not match.</returns>
+        public bool MisconfiguredPrereleaseAndSemVer1()
+        {
+            return this.VersionOptions != null && this.VersionOptions.NuGetPackageVersion != null && this.VersionOptions.NuGetPackageVersion.SemVer == 1 && this.PrereleaseVersion != MakePrereleaseSemVer1Compliant(this.PrereleaseVersion, 0);
+        }
+
         /// <summary>
         /// Gets the build metadata, compliant to the NuGet-compatible subset of SemVer 1.0.
         /// </summary>

src/Nerdbank.GitVersioning.Tasks/GetBuildVersion.cs

@@ -202,6 +202,11 @@ protected override bool ExecuteInner()
                     oracle.BuildMetadata.AddRange(this.BuildMetadata);
                 }
 
+                if (oracle.MisconfiguredPrereleaseAndSemVer1())
+                {
+                    this.Log.LogWarning("The 'nugetPackageVersion' is explicitly set to 'semVer': 1 but the prerelease version '{0}' is not SemVer1 compliant. Change the 'nugetPackageVersion'.'semVer' value to 2 or chagne the 'version' member to follow SemVer1 (like: '{1}').", oracle.PrereleaseVersion, oracle.SemVer1WithoutPaddingOrBuildMetadata);
+                }
+
                 this.PublicRelease = oracle.PublicRelease;
                 this.Version = oracle.Version.ToString();
                 this.AssemblyVersion = oracle.AssemblyVersion.ToString();