Relax SemanticVersion constructors to not require minor and patch (Po…

…werShell#3696)

`$psversiontable.psversion -gt "3.0"` which is used by PowerShellGet to determine if a module is compatible with the current version of PowerShell.

Change is to allow specifying only major or major+minor where the missing segments default to zero by providing overloaded constructors and allow
the string parsing method to not require major, minor, and patch segments to all be specified (only major is required).

Based on the [response](semver/semver#368) from the maintainer of semver, there is no requirement to have strict
conformance for the inputs to the constructor and allowing "3.0" to result in a semver of 3.0.0 is reasonable.

src/System.Management.Automation/engine/PSVersionInfo.cs

@@ -465,6 +465,25 @@ public SemanticVersion(int major, int minor, int patch)
             Label = null;
         }
 
+        /// <summary>
+        /// Construct a SemanticVersion.
+        /// </summary>
+        /// <param name="major">The major version</param>
+        /// <param name="minor">The minor version</param>
+        /// <exception cref="PSArgumentException">
+        /// If <paramref name="major"/> or <paramref name="minor"/> is less than 0.
+        /// </exception>
+        public SemanticVersion(int major, int minor) : this(major, minor, 0) {}
+
+        /// <summary>
+        /// Construct a SemanticVersion.
+        /// </summary>
+        /// <param name="major">The major version</param>
+        /// <exception cref="PSArgumentException">
+        /// If <paramref name="major"/> is less than 0.
+        /// </exception>
+        public SemanticVersion(int major) : this(major, 0, 0) {}
+
         private const string LabelPropertyName = "PSSemanticVersionLabel";
 
         /// <summary>
@@ -584,24 +603,24 @@ private static bool TryParseVersion(string version, ref VersionResult result)
 
             var versionSansLabel = (dashIndex < 0) ? version : version.Substring(0, dashIndex);
             string[] parsedComponents = versionSansLabel.Split(Utils.Separators.Dot);
-            if (parsedComponents.Length != 3)
+            if (parsedComponents.Length > 3)
             {
                 result.SetFailure(ParseFailureKind.ArgumentException);
                 return false;
             }
 
-            int major, minor, patch;
+            int major = 0, minor = 0, patch = 0;
             if (!TryParseComponent(parsedComponents[0], "major", ref result, out major))
             {
                 return false;
             }
 
-            if (!TryParseComponent(parsedComponents[1], "minor", ref result, out minor))
+            if (parsedComponents.Length >= 2 && !TryParseComponent(parsedComponents[1], "minor", ref result, out minor))
             {
                 return false;
             }
 
-            if (!TryParseComponent(parsedComponents[2], "patch", ref result, out patch))
+            if (parsedComponents.Length == 3 && !TryParseComponent(parsedComponents[2], "patch", ref result, out patch))
             {
                 return false;
             }

test/powershell/engine/SemanticVersion.Tests.ps1

@@ -17,6 +17,20 @@ Describe "SemanticVersion api tests" -Tags 'CI' {
             $v.Patch | Should Be 0
             $v.Label | Should BeNullOrEmpty
             $v.ToString() | Should Be "1.0.0"
+
+            $v = [SemanticVersion]::new("3.0")
+            $v.Major | Should Be 3
+            $v.Minor | Should Be 0
+            $v.Patch | Should Be 0
+            $v.Label | Should BeNullOrEmpty
+            $v.ToString() | Should Be "3.0.0"
+
+            $v = [SemanticVersion]::new("2")
+            $v.Major | Should Be 2
+            $v.Minor | Should Be 0
+            $v.Patch | Should Be 0
+            $v.Label | Should BeNullOrEmpty
+            $v.ToString() | Should Be "2.0.0"
         }
 
 	    # After the above test, we trust the properties and rely on ToString for validation
@@ -27,6 +41,12 @@ Describe "SemanticVersion api tests" -Tags 'CI' {
 
             $v = [SemanticVersion]::new(3, 2, 0, "beta.1")
             $v.ToString() | Should Be "3.2.0-beta.1"
+
+            $v = [SemanticVersion]::new(3, 1)
+            $v.ToString() | Should Be "3.1.0"
+
+            $v = [SemanticVersion]::new(3)
+            $v.ToString() | Should Be "3.0.0"
         }
 
         It "version arg constructor" {
@@ -57,6 +77,8 @@ Describe "SemanticVersion api tests" -Tags 'CI' {
             @{ lhs = $v1_0_0_alpha; rhs = $v1_0_0_beta }
             @{ lhs = $v1_0_0_alpha; rhs = $v1_0_0 }
             @{ lhs = $v1_0_0_beta; rhs = $v1_0_0 }
+            @{ lhs = $v2_1_0; rhs = "3.0"}
+            @{ lhs = "1.5"; rhs = $v2_1_0}
         )
         It "less than" -TestCases $testCases {
             param($lhs, $rhs)
@@ -121,8 +143,8 @@ Describe "SemanticVersion api tests" -Tags 'CI' {
             @{ expectedResult = $false; version = "" }
             @{ expectedResult = $false; version = "1.0.0-" }
             @{ expectedResult = $false; version = "-" }
+            @{ expectedResult = $false; version = "." }
             @{ expectedResult = $false; version = "-alpha" }
-	        @{ expectedResult = $false; version = "1.0" }  # REVIEW - should this be allowed
 	        @{ expectedResult = $false; version = "1..0" }
 	        @{ expectedResult = $false; version = "1.0.-alpha" }
 	        @{ expectedResult = $false; version = "1.0." }
@@ -178,10 +200,6 @@ Describe "SemanticVersion api tests" -Tags 'CI' {
             # Revision isn't supported
             { [SemanticVersion]::new([Version]::new(0, 0, 0, 4)) } | Should Throw # PSArgumentException
             { [SemanticVersion]::new([Version]::new("1.2.3.4")) } | Should Throw # PSArgumentException
-
-            # Build is required
-            { [SemanticVersion]::new([Version]::new(1, 2)) } | Should Throw # PSArgumentException
-            { [SemanticVersion]::new([Version]::new("1.2")) } | Should Throw # PSArgumentException
         }
     }