Correct parsing of 'Format Version' header in sln files

Prior to this change the exception on line 138 could not
be thrown, as far as I can tell. The reason for this
is that`HeaderPrefix` contained a trailing space, and we
had verified that `line` (trimmed) started with
`HeaderPrefix`. Hence `line` must contain something more
than `HeaderPrefix` otherwise the tailing space would
have been removed, so the length of `line` could not be
less than or equal to the length of `HeaderPrefix`.

Added and changed tests to ensure that both exceptions
regarding `FormatVersion` are thrown.

Fixes #5978

src/Microsoft.DotNet.Cli.Sln.Internal/LocalizableStrings.cs

@@ -17,7 +17,9 @@ internal class LocalizableStrings
 
         public const string GlobalSectionNotClosedError = "Global section not closed";
 
-        public const string FileHeaderMissingError = "File header is missing";
+        public const string FileHeaderMissingVersionError = "File header is missing version";
+
+        public const string FileHeaderMissingError = "Expected file header not found";
 
         public const string ProjectSectionNotClosedError = "Project section not closed";
 

src/Microsoft.DotNet.Cli.Sln.Internal/SlnFile.cs

@@ -120,7 +120,7 @@ public static SlnFile Read(string file)
 
         private void Read(TextReader reader)
         {
-            const string HeaderPrefix = "Microsoft Visual Studio Solution File, Format Version ";
+            const string HeaderPrefix = "Microsoft Visual Studio Solution File, Format Version";
 
             string line;
             int curLineNum = 0;
@@ -137,10 +137,10 @@ private void Read(TextReader reader)
                     {
                         throw new InvalidSolutionFormatException(
                             curLineNum,
-                            LocalizableStrings.FileHeaderMissingError);
+                            LocalizableStrings.FileHeaderMissingVersionError);
                     }
 
-                    FormatVersion = line.Substring(HeaderPrefix.Length);
+                    FormatVersion = line.Substring(HeaderPrefix.Length).Trim();
                     _prefixBlankLines = curLineNum - 1;
                 }
                 if (line.StartsWith("# ", StringComparison.Ordinal))
@@ -199,9 +199,7 @@ private void Read(TextReader reader)
             }
             if (FormatVersion == null)
             {
-                throw new InvalidSolutionFormatException(
-                    curLineNum,
-                    LocalizableStrings.FileHeaderMissingError);
+                throw new InvalidSolutionFormatException(LocalizableStrings.FileHeaderMissingError);
             }
         }
 
@@ -1167,6 +1165,11 @@ protected override void ClearItems()
 
     public class InvalidSolutionFormatException : Exception
     {
+        public InvalidSolutionFormatException(string details)
+            : base(details)
+        {
+        }
+
         public InvalidSolutionFormatException(int line, string details)
             : base(string.Format(LocalizableStrings.ErrorMessageFormatString, line, details))
         {

test/Microsoft.DotNet.Cli.Sln.Internal.Tests/Microsoft.DotNet.Cli.Sln.Internal.Tests.cs

@@ -287,9 +287,29 @@ public void WhenGivenAValidSlnFileItModifiesSavesAndVerifiesContents()
                 .Should().Be(SolutionModified);
         }
 
+        [Theory]
+        [InlineData("Microsoft Visual Studio Solution File, Format Version ", 1)]
+        [InlineData("First Line\nMicrosoft Visual Studio Solution File, Format Version ", 2)]
+        [InlineData("First Line\nMicrosoft Visual Studio Solution File, Format Version \nThird Line", 2)]
+        [InlineData("First Line\nSecondLine\nMicrosoft Visual Studio Solution File, Format Version \nFourth Line", 3)]
+        public void WhenGivenASolutionWithMissingHeaderVersionItThrows(string fileContents, int lineNum)
+        {
+            var tmpFile = Temp.CreateFile();
+            tmpFile.WriteAllText(fileContents);
+
+            Action action = () =>
+            {
+                SlnFile.Read(tmpFile.Path);
+            };
+
+            action.ShouldThrow<InvalidSolutionFormatException>()
+                .WithMessage($"Invalid format in line {lineNum}: File header is missing version");
+        }
+
         [Theory]
         [InlineData("Invalid Solution")]
-        [InlineData("Microsoft Visual Studio Solution File, Format Version ")]
+        [InlineData("Invalid Solution\nSpanning Multiple Lines")]
+        [InlineData("Microsoft Visual\nStudio Solution File,\nFormat Version ")]
         public void WhenGivenASolutionWithMissingHeaderItThrows(string fileContents)
         {
             var tmpFile = Temp.CreateFile();
@@ -301,7 +321,7 @@ public void WhenGivenASolutionWithMissingHeaderItThrows(string fileContents)
             };
 
             action.ShouldThrow<InvalidSolutionFormatException>()
-                .WithMessage("Invalid format in line 1: File header is missing");
+                .WithMessage("Expected file header not found");
         }
 
         [Fact]