Hard fail to prevent IndentSize of <= 0 to avoid any issues.

closes #1736

Author: belav

Src/CSharpier.Cli.Tests/CliTests.cs

@@ -743,6 +743,19 @@ public async Task Format_Should_Reformat_When_Options_Change_With_Cache()
         result.Should().Contain("\n\t// break\n");
     }
 
+    [Test]
+    public async Task Format_Should_Throw_With_IndentSize_Zero()
+    {
+        var unformattedContent = "public class ClassName { \n// break\n }\n";
+
+        await WriteFileAsync("Unformatted.cs", unformattedContent);
+        await WriteFileAsync(".csharpierrc", "indentSize: 0");
+        var result = await new CsharpierProcess().WithArguments("format .").ExecuteAsync();
+
+        result.ExitCode.Should().Be(1);
+        result.ErrorOutput.Should().Contain("An indent size of 0 is not valid");
+    }
+
     [Test]
     public void Format_Should_Handle_Concurrent_Processes()
     {

Src/CSharpier.Core/PrinterOptions.cs

@@ -4,10 +4,24 @@ namespace CSharpier.Core;
 
 internal class PrinterOptions(Formatter formatter)
 {
+    private int indentSize = formatter == Formatter.XML ? 2 : 4;
     public bool IncludeAST { get; init; }
     public bool IncludeDocTree { get; init; }
     public bool UseTabs { get; set; }
-    public int IndentSize { get; set; } = formatter == Formatter.XML ? 2 : 4;
+
+    public int IndentSize
+    {
+        get => this.indentSize;
+        set
+        {
+            if (value <= 0)
+            {
+                throw new ArgumentException("An indent size of 0 is not valid");
+            }
+            this.indentSize = value;
+        }
+    }
+
     public int Width { get; set; } = 100;
     public EndOfLine EndOfLine { get; set; } = EndOfLine.Auto;
     public bool TrimInitialLines { get; init; } = true;