Don't show missing version warning for absoluteLatest (#8199)

Address #8198

Author: joelverhagen

src/NuGetGallery/Controllers/PackagesController.cs

@@ -828,6 +828,10 @@ public HttpStatusCodeResult DisplayPackage()
         [HttpGet]
         public virtual async Task<ActionResult> DisplayPackage(string id, string version)
         {
+            // Attempt to normalize the version but allow version strings that are not actually SemVer strings. For
+            // example, "absoluteLatest" is allowed as the version string as a reference to the absolute latest version
+            // including prerelease versions. In this case, the resulting normalized version will be left as the
+            // original string.
             string normalized = NuGetVersionFormatter.Normalize(version);
             if (!string.Equals(version, normalized))
             {
@@ -890,7 +894,11 @@ public virtual async Task<ActionResult> DisplayPackage(string id, string version
                 model.GitHubDependenciesInformation = _contentObjectService.GitHubUsageConfiguration.GetPackageInformation(id);
             }
 
-            if (normalized != null && !string.Equals(package.NormalizedVersion, normalized, StringComparison.OrdinalIgnoreCase))
+            // If the normalized version is actually a SemVer but does not match the resolved package version, show a
+            // warning. It's possible that the normalized version is not a SemVer string (like "absoluteLatest").
+            if (normalized != null
+                && !string.Equals(package.NormalizedVersion, normalized, StringComparison.OrdinalIgnoreCase)
+                && NuGetVersion.TryParse(normalized, out var parsed))
             {
                 model.VersionRequested = normalized;
                 model.VersionRequestedWasNotFound = true;

tests/NuGetGallery.Facts/Controllers/PackagesControllerFacts.cs

@@ -896,6 +896,7 @@ public async Task GivenAnAbsoluteLatestVersionItReturnsTheFirstLatestSemVer2()
                 // The page should select the first package that is IsLatestSemVer2
                 Assert.Equal(latestPackage.NormalizedVersion, model.Version);
                 Assert.True(model.LatestVersionSemVer2);
+                Assert.False(model.VersionRequestedWasNotFound);
 
                 deprecationService.Verify();
             }