Suggest file names Windows accepts on every platform [patch]

ImageDescriber.Test/ScanTests.cs

@@ -87,6 +87,44 @@ public void SanitizeFileNameHandlesSimpleName()
 		Assert.AreEqual("sunset-over-ocean.webp", result.WeakString);
 	}
 
+	[TestMethod]
+	public void SanitizeFileNameReplacesCharactersWindowsRejectsOnEveryPlatform()
+	{
+		// Path.GetInvalidFileNameChars() is only "\0" and "/" on Linux and macOS, so this used to
+		// come back unchanged there and produce a name Windows cannot hold
+		FileName result = Scan.SanitizeFileName("sunset at 5:30pm? <draft>", ".jpg".As<FileExtension>());
+
+		Assert.AreEqual("sunset at 5-30pm- -draft.jpg", result.WeakString);
+	}
+
+	[TestMethod]
+	public void SanitizeFileNameReplacesEveryWindowsReservedCharacterAndControlCharacter()
+	{
+		FileName result = Scan.SanitizeFileName("a<b>c:d\"e|f?g*h\\i\tj\u0001k", ".jpg".As<FileExtension>());
+
+		Assert.AreEqual("a-b-c-d-e-f-g-h-i-j-k.jpg", result.WeakString);
+	}
+
+	[TestMethod]
+	[DataRow("con")]
+	[DataRow("NUL")]
+	[DataRow("Com1")]
+	[DataRow("lpt9")]
+	public void SanitizeFileNameAvoidsWindowsDeviceNames(string suggestion)
+	{
+		FileName result = Scan.SanitizeFileName(suggestion, ".jpg".As<FileExtension>());
+
+		Assert.AreEqual($"{suggestion}-image.jpg", result.WeakString);
+	}
+
+	[TestMethod]
+	public void SanitizeFileNameKeepsNamesThatOnlyStartWithADeviceName()
+	{
+		FileName result = Scan.SanitizeFileName("console-on-desk", ".jpg".As<FileExtension>());
+
+		Assert.AreEqual("console-on-desk.jpg", result.WeakString);
+	}
+
 	[TestMethod]
 	public void SanitizeFileNameTakesNameFromInsideCodeFence()
 	{

ImageDescriber/Verbs/Scan.cs

@@ -267,11 +267,10 @@ internal static FileName SanitizeFileName(string rawSuggestion, FileExtension ex
 			name = System.IO.Path.GetFileNameWithoutExtension(name);
 		}
 
-		// Remove invalid filename characters
-		foreach (char c in System.IO.Path.GetInvalidFileNameChars())
-		{
-			name = name.Replace(c, '-');
-		}
+		// Remove characters Windows rejects. Path.GetInvalidFileNameChars() is only "\0" and "/" on
+		// Linux and macOS, and a suggestion is stored once per hash and meant for renaming, so a name
+		// suggested there has to be legal on Windows, NTFS, SMB and exFAT as well
+		name = string.Concat(name.Select(c => IsPortableFileNameChar(c) ? c : '-'));
 
 		// Collapse multiple hyphens and trim
 		while (name.Contains("--", StringComparison.Ordinal))
@@ -286,9 +285,26 @@ internal static FileName SanitizeFileName(string rawSuggestion, FileExtension ex
 			name = "unnamed";
 		}
 
+		// Windows refuses a device name as a file name whatever extension follows it ("con.jpg")
+		if (WindowsReservedNames.Contains(name))
+		{
+			name = $"{name}-image";
+		}
+
 		return $"{name}{extension}".As<FileName>();
 	}
 
+	private static readonly HashSet<string> WindowsReservedNames = new(
+		[
+			"CON", "PRN", "AUX", "NUL",
+			"COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8", "COM9",
+			"LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9",
+		],
+		StringComparer.OrdinalIgnoreCase);
+
+	private static bool IsPortableFileNameChar(char c) =>
+		c is >= ' ' and not ('<' or '>' or ':' or '"' or '/' or '\\' or '|' or '?' or '*');
+
 	// An opening or closing fence ("```" or "```text"), as opposed to a name written inline
 	// between two fences on one line ("```sunset```")
 	private static bool IsCodeFence(string line) =>