Add UNT0044

doc/UNT0044.md

@@ -0,0 +1,69 @@
+# UNT0044 Avoid temporary strings when setting TextMeshPro text
+
+TextMeshPro can consume a `StringBuilder` or character array directly and can format numeric arguments into its internal buffer. These overloads can avoid constructing an intermediate string.
+
+This is an **allocation-reduction suggestion, not a guarantee of faster text updates**. It does not recommend replacing assignments of existing strings or string literals with `SetText(string)`.
+
+## Flagged code and possible alternatives
+
+Each row is an independent before/after example for a `TMP_Text`, `TextMeshPro`, or `TextMeshProUGUI` instance. The alternatives require the behavioral review described below; they are not automatic fixes.
+
+| Case | Code flagged by the analyzer (before) | Possible alternative (after) |
+| --- | --- | --- |
+| Builder assigned to `text` | `label.text = builder.ToString();` | `label.SetText(builder);` |
+| Builder passed to `SetText` | `label.SetText(builder.ToString());` | `label.SetText(builder);` |
+| Character array | `label.text = new string(characters);` | `label.SetText(characters);` |
+| Character-array slice | `label.SetText(new string(characters, start, length));` | `label.SetText(characters, start, length);` |
+| Number with a prefix | `label.text = $"Score: {score}";` | `label.SetText("Score: {0}", score);` |
+| Number without a prefix | `label.SetText(score.ToString());` | `label.SetText("{0}", score);` |
+
+The last two rows are separate cases: one displays `"Score: "` followed by the number, while the other displays only the number. `SetText(score.ToString())` is a flagged input pattern, **not** the optimization. Both numeric alternatives pass the number directly to TMP without first formatting it into a string.
+
+## Scope
+
+The analyzer recognizes direct, parameterless `StringBuilder.ToString()` calls, character-array string constructors, and simple numeric interpolation or parameterless numeric `ToString()` calls. It checks that the corresponding public `SetText` overload exists in the referenced TMP API.
+
+Numeric suggestions are limited to `byte`, `sbyte`, `short`, `ushort`, `int`, `uint`, and `float`, and the number of arguments supported by the installed API. Known constant range or precision losses are excluded. This does **not** prove that variable values or their displayed formatting will be preserved.
+
+The analyzer does not flag custom formatting, alignment, mixed string/numeric interpolation, literal braces in interpolation, `double`, `decimal`, `long`, `ulong`, or nullable numeric values. It also leaves compound/value-producing assignments, separately stored strings, explicit extra `SetText` arguments, and custom `text`/`SetText` members alone.
+
+## Applying an alternative
+
+TMP copies these buffers during the call; it does not retain the caller's buffer for later reading. The caller can reuse it after the call returns.
+
+For numeric text, select the numeric overload only when TMP's formatting, precision, and supported range meet the application's requirements. It is not a mechanical replacement for .NET interpolation or `ToString()`.
+
+**No automatic code fix is provided.** Even changing an existing `SetText(builder.ToString())` call to `SetText(builder)` can change observable behavior.
+
+## Why an automatic replacement is unsafe
+
+| Concern | Difference |
+| --- | --- |
+| Unchanged text | The `text` setter can return early for equal strings. `SetText` processes its input and marks vertices/layout dirty without that equality check. |
+| Preprocessing | String input uses `ITextPreprocessor` during `ParseInputText`. Buffer and numeric input take paths that bypass it in the inspected implementations. |
+| Numeric formatting | TMP is not a .NET composite formatter. Culture, precision, rounding, standard format strings, alignment, and escaped braces differ. Values are converted through `float`, `decimal`, and `long`; checking only the integer-to-float conversion is insufficient. |
+| Nulls and slices | A null builder's `ToString()` throws, while TMP accepts a null buffer. String constructors validate array slices; TMP uses different bounds handling. The `StringBuilder` slice overload is not public. |
+| Property behavior | `text` is virtual. Calling `SetText` can bypass an override and can change dirty callbacks. Resolving a property to the base declaration does not prove that its runtime receiver has no override. |
+| Reading text back | Reading `text` after a buffer/numeric update can materialize a string again. Code that depends on the getter needs separate review. |
+
+## Performance evidence and limitations
+
+For nonempty input, `StringBuilder.ToString()` and character-array string construction allocate and copy a string. TMP's buffer overloads instead copy directly into TMP-owned storage. Its numeric overloads write formatted characters into that storage without first producing a formatted string.
+
+That establishes an opportunity to remove an intermediate allocation, **not** a universal CPU-time improvement or a zero-allocation guarantee. TMP's buffers can grow, parsing and rendering still cost time, and reading `text` can allocate. In the inspected sources, `UNITY_EDITOR` paths also reconstruct the backing string, so Editor allocation results differ from player builds. Repeated unchanged updates can cost more after losing the property setter's early-out.
+
+This is source-level evidence, not comparative benchmark evidence. Profile the complete update in a warmed-up player build, including unchanged-text cases, before claiming an application-level speedup.
+
+## Other related candidates
+
+`SetCharArray` provides the character-buffer alternatives as well. Some TMP APIs also expose `SetText(ReadOnlySpan<char>)`, making `span.ToString()` and `new string(span)` further candidates for manual review. Availability of those span overloads depends on the referenced API; they are not covered by this diagnostic.
+
+## Sources
+
+- [Unity's TMP SetText API documentation](https://docs.unity3d.com/Packages/com.unity.textmeshpro@3.0/api/TMPro.TMP_Text.SetText.html).
+- [TMP text property and equality early-out](https://github.com/needle-mirror/com.unity.textmeshpro/blob/5671be34032f3ead7e4f94de2bfa6f7a24513cdb/Scripts/Runtime/TMP_Text.cs#L114-L134), in the public package mirror.
+- [TMP string and numeric SetText implementations](https://github.com/needle-mirror/com.unity.textmeshpro/blob/5671be34032f3ead7e4f94de2bfa6f7a24513cdb/Scripts/Runtime/TMP_Text.cs#L2290-L2568).
+- [TMP StringBuilder and character-array overloads](https://github.com/needle-mirror/com.unity.textmeshpro/blob/5671be34032f3ead7e4f94de2bfa6f7a24513cdb/Scripts/Runtime/TMP_Text.cs#L2577-L2677), including their Editor paths.
+- [TMP preprocessing paths](https://github.com/needle-mirror/com.unity.textmeshpro/blob/5671be34032f3ead7e4f94de2bfa6f7a24513cdb/Scripts/Runtime/TMP_Text.cs#L1885-L1899) and [numeric conversion/formatting](https://github.com/needle-mirror/com.unity.textmeshpro/blob/5671be34032f3ead7e4f94de2bfa6f7a24513cdb/Scripts/Runtime/TMP_Text.cs#L3531-L3595).
+- [.NET StringBuilder.ToString implementation](https://github.com/dotnet/runtime/blob/d099f075e45d2aa6007a22b71b45a08758559f80/src/libraries/System.Private.CoreLib/src/System/Text/StringBuilder.cs#L334-L369) and [character-array string constructors](https://github.com/dotnet/runtime/blob/d099f075e45d2aa6007a22b71b45a08758559f80/src/libraries/System.Private.CoreLib/src/System/String.cs#L66-L108).
+- [Unity's string SetText implementation](https://github.com/Unity-Technologies/uGUI/blob/be962f3bc3208f8df3abd8e8ddfae63ecb24f8c9/com.unity.ugui/Runtime/TMP/TMP_Text.cs#L2647-L2663) and [span overloads](https://github.com/Unity-Technologies/uGUI/blob/be962f3bc3208f8df3abd8e8ddfae63ecb24f8c9/com.unity.ugui/Runtime/TMP/TMP_Text.cs#L2930-L2962).

doc/index.md

@@ -45,6 +45,7 @@ ID | Title | Category
 [UNT0041](UNT0041.md) | Use `Animator.StringToHash` for repeated `Animator` method calls | Performance
 [UNT0042](UNT0042.md) | `Mesh` array property accessed in loop | Performance
 [UNT0043](UNT0043.md) | Possible typo in conditional compilation symbol | Correctness
+[UNT0044](UNT0044.md) | Avoid temporary strings when setting TextMeshPro text | Performance
 
 # Diagnostic Suppressors
 
@@ -73,4 +74,3 @@ ID | Suppressed ID | Justification
 [USP0021](USP0021.md) | IDE0041 | Prefer reference equality
 [USP0022](USP0022.md) | IDE0270 | Unity objects should not use if null coalescing
 [USP0023](USP0023.md) | IDE1006 | The Unity runtime invokes Unity messages
-

src/Microsoft.Unity.Analyzers.Tests/Infrastructure/DiagnosticVerifier.cs

@@ -24,6 +24,9 @@ public abstract class DiagnosticVerifier
 	private const string CSharpDefaultFileExt = "cs";
 	private const string TestProjectName = "TestProject";
 
+	private static readonly Lazy<ImmutableArray<MetadataReference>> _references = new(
+		() => [.. UnityAssemblies().Select(path => MetadataReference.CreateFromFile(path))]);
+
 	protected abstract DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer();
 
 	protected virtual IEnumerable<DiagnosticAnalyzer> GetRelatedAnalyzers(DiagnosticAnalyzer analyzer)
@@ -340,21 +343,26 @@ protected static IEnumerable<string> UnityAssemblies()
 		var managed = Path.Combine(scripting, "Managed");
 
 		yield return Path.Combine(managed, "UnityEditor.dll");
-		yield return Path.Combine(managed, "UnityEngine.dll");
 
-		var monolib = Path.Combine(scripting, "MonoBleedingEdge", "lib", "mono", "4.7.1-api");
-		yield return Path.Combine(monolib, "mscorlib.dll");
-		yield return Path.Combine(monolib, "System.dll");
+		// Package assemblies reference Unity's modules rather than the combined reference assembly.
+		foreach (var assembly in Directory.EnumerateFiles(Path.Combine(managed, "UnityEngine"), "*.dll"))
+			yield return assembly;
+
+		var netstandard = Path.Combine(scripting, "NetStandard");
+		yield return Path.Combine(netstandard, "ref", "2.1.0", "netstandard.dll");
 
-		var facades = Path.Combine(monolib, "Facades");
-		yield return Path.Combine(facades, "netstandard.dll");
+		var shims = Path.Combine(netstandard, "compat", "2.1.0", "shims", "netfx");
+		foreach (var assembly in Directory.EnumerateFiles(shims, "*.dll"))
+			yield return assembly;
 
 		// Use the 2D template to get additional assemblies, normally acquired through Package Manager
 		var libcache = Path.Combine(resources, "PackageManager", "ProjectTemplates", "libcache");
 		var template2d = Directory.GetDirectories(libcache, "com.unity.template.2d-*").Single();
 		var template2dScriptAssemblies = Path.Combine(template2d, "ScriptAssemblies");
 
 		yield return Path.Combine(template2dScriptAssemblies, "Unity.Mathematics.dll");
+		yield return Path.Combine(template2dScriptAssemblies, "UnityEngine.UI.dll");
+		yield return Path.Combine(template2dScriptAssemblies, "Unity.TextMeshPro.dll");
 	}
 
 	private static Project CreateProject(AnalyzerVerificationContext context, string[] sources)
@@ -365,7 +373,7 @@ private static Project CreateProject(AnalyzerVerificationContext context, string
 			.CurrentSolution
 			.AddProject(projectId, TestProjectName, TestProjectName, LanguageNames.CSharp);
 
-		solution = UnityAssemblies().Aggregate(solution, (current, dll) => current.AddMetadataReference(projectId, MetadataReference.CreateFromFile(dll)));
+		solution = solution.AddMetadataReferences(projectId, _references.Value);
 
 		var parseOptions = new CSharpParseOptions(context.LanguageVersion)
 			.WithPreprocessorSymbols(context.PreprocessorSymbols);