Add Analyzer to require checking or discarding `TryGetValue`

I'm pretty sure all the existing instances were intended to use `default(T)` if
the key isn't present, except maybe the cheatcode converters but I don't care to
rewrite those at the moment

Common.ruleset

@@ -31,6 +31,9 @@
 		<!-- Don't call typeof(T).ToString(), use nameof operator or typeof(T).FullName -->
 		<Rule Id="BHI1103" Action="Error" />
 
+		<!-- Check result of IDictionary.TryGetValue, or discard it if default(T) is desired -->
+		<Rule Id="BHI1200" Action="Error" />
+
 		<!-- Call to FirstOrDefault when elements are of a value type; FirstOrNull may have been intended -->
 		<Rule Id="BHI3100" Action="Error" />
 

ExternalProjects/AnalyzersCommon/RoslynUtils.cs

@@ -26,4 +26,16 @@ public static class RoslynUtils
 
 	public static bool Matches(this ISymbol expected, ISymbol? actual)
 		=> SymbolEqualityComparer.Default.Equals(expected, actual);
+
+#if false // easier to just `.OriginalDefinition` always
+	public static bool Matches(this INamedTypeSymbol expected, INamedTypeSymbol? actual, bool degenericise)
+	{
+		if (degenericise)
+		{
+			if (expected.IsGenericType && !expected.IsUnboundGenericType) return expected.OriginalDefinition.Matches(actual, degenericise: true);
+			if (actual is not null && actual.IsGenericType && !actual.IsUnboundGenericType) return expected.Matches(actual.OriginalDefinition, degenericise: true);
+		}
+		return expected.Matches(actual as ISymbol);
+	}
+#endif
 }

ExternalProjects/BizHawk.Analyzer/TryGetValueImplicitDiscardAnalyzer.cs

@@ -0,0 +1,56 @@
+namespace BizHawk.Analyzers;
+
+using System.Collections.Immutable;
+using System.Linq;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class TryGetValueImplicitDiscardAnalyzer : DiagnosticAnalyzer
+{
+	private static readonly DiagnosticDescriptor DiagUncheckedTryGetValue = new(
+		id: "BHI1200",
+		title: "Check result of IDictionary.TryGetValue, or discard it if default(T) is desired",
+		messageFormat: "Assign the result of this TryGetValue call to a variable or discard",
+		category: "Usage",
+		defaultSeverity: DiagnosticSeverity.Error,
+		isEnabledByDefault: true);
+
+	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(DiagUncheckedTryGetValue);
+
+	public override void Initialize(AnalysisContext context)
+	{
+		context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+		context.EnableConcurrentExecution();
+		context.RegisterCompilationStartAction(static initContext =>
+		{
+			const string STR_TGV = "TryGetValue";
+			var rwDictSym = initContext.Compilation.GetTypeByMetadataName("System.Collections.Generic.IDictionary`2")!;
+			var roDictSym = initContext.Compilation.GetTypeByMetadataName("System.Collections.Generic.IReadOnlyDictionary`2")!;
+			bool IsBCLTryGetValue(IMethodSymbol calledSym)
+				=> calledSym.ContainingType.AllInterfaces.Any(intfSym =>
+					{
+						var degenericisedSym = intfSym.OriginalDefinition;
+						return rwDictSym.Matches(degenericisedSym) || roDictSym.Matches(degenericisedSym);
+					});
+			initContext.RegisterOperationAction(
+				oac =>
+				{
+					var operation = (IInvocationOperation) oac.Operation;
+					if (operation.Parent?.Kind is not OperationKind.ExpressionStatement) return;
+					var calledSym = operation.TargetMethod.ConstructedFrom;
+					if (calledSym.Name is STR_TGV) oac.ReportDiagnostic(Diagnostic.Create(
+						DiagUncheckedTryGetValue,
+						operation.Syntax.GetLocation(),
+						IsBCLTryGetValue(calledSym) ? DiagnosticSeverity.Error : DiagnosticSeverity.Warning,
+						additionalLocations: null,
+						properties: null,
+						messageArgs: null));
+				},
+				OperationKind.Invocation);
+		});
+	}
+}

src/BizHawk.Bizware.BizwareGL/Pipeline.cs

@@ -66,7 +66,7 @@ namespace BizHawk.Bizware.BizwareGL
 
 		public PipelineUniform TryGetUniform(string name)
 		{
-			Uniforms.TryGetValue(name, out var ret);
+			_ = Uniforms.TryGetValue(name, out var ret);
 			return ret;
 		}
 

src/BizHawk.Bizware.DirectX/DirectInputAdapter.cs

@@ -54,8 +54,8 @@ namespace BizHawk.Bizware.DirectX
 					continue;
 				for (int b = 0, n = pad.NumButtons; b < n; b++) handleButton(pad.InputNamePrefix + pad.ButtonName(b), pad.Pressed(b), ClientInputFocus.Pad);
 				foreach (var (axisName, f) in pad.GetAxes()) handleAxis(pad.InputNamePrefix + axisName, (int) f);
-				_lastHapticsSnapshot.TryGetValue(pad.InputNamePrefix + "Left", out var leftStrength);
-				_lastHapticsSnapshot.TryGetValue(pad.InputNamePrefix + "Right", out var rightStrength);
+				_ = _lastHapticsSnapshot.TryGetValue(pad.InputNamePrefix + "Left", out var leftStrength);
+				_ = _lastHapticsSnapshot.TryGetValue(pad.InputNamePrefix + "Right", out var rightStrength);
 				pad.SetVibration(leftStrength, rightStrength); // values will be 0 if not found
 			}
 			foreach (var pad in GamePad.EnumerateDevices())

src/BizHawk.Client.Common/DisplayManager/FilterManager.cs

@@ -47,7 +47,7 @@ namespace BizHawk.Client.Common.FilterManager
 		{
 			get
 			{
-				_filterNameIndex.TryGetValue(name, out var ret);
+				_ = _filterNameIndex.TryGetValue(name, out var ret);
 				return ret;
 			}
 		}

src/BizHawk.Client.Common/RomLoader.cs

@@ -379,7 +379,7 @@ namespace BizHawk.Client.Common
 			}
 			else
 			{
-				_config.PreferredCores.TryGetValue(cip.Game.System, out var preferredCore);
+				_ = _config.PreferredCores.TryGetValue(cip.Game.System, out var preferredCore);
 				var dbForcedCoreName = cip.Game.ForcedCore;
 				cores = CoreInventory.Instance.GetCores(cip.Game.System)
 					.OrderBy(c =>

src/BizHawk.Client.Common/cheats/GbGgGameGenieDecoder.cs

@@ -52,20 +52,20 @@ namespace BizHawk.Client.Common.cheats
 			// Getting Value
 			if (_code.Length > 0)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[0], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[0], out x);
 				result.Value = x << 4;
 			}
 
 			if (_code.Length > 1)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[1], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[1], out x);
 				result.Value |= x;
 			}
 
 			// Address
 			if (_code.Length > 2)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[2], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[2], out x);
 				result.Value = x << 8;
 			}
 			else
@@ -75,30 +75,30 @@ namespace BizHawk.Client.Common.cheats
 
 			if (_code.Length > 3)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[3], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[3], out x);
 				result.Address |= x << 4;
 			}
 
 			if (_code.Length > 4)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[4], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[4], out x);
 				result.Address |= x;
 			}
 
 			if (_code.Length > 5)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[5], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[5], out x);
 				result.Address |= (x ^ 0xF) << 12;
 			}
 
 			// compare need to be full
 			if (_code.Length > 8)
 			{
-				_gbGgGameGenieTable.TryGetValue(_code[6], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[6], out x);
 				var comp = x << 2;
 
 				// 8th character ignored
-				_gbGgGameGenieTable.TryGetValue(_code[8], out x);
+				_ = _gbGgGameGenieTable.TryGetValue(_code[8], out x);
 				comp |= (x & 0xC) >> 2;
 				comp |= (x & 0x3) << 6;
 				result.Compare = comp ^ 0xBA;

src/BizHawk.Client.Common/cheats/GenesisGameGenieDecoder.cs

@@ -65,7 +65,7 @@ namespace BizHawk.Client.Common.cheats
 			foreach (var t in code)
 			{
 				hexCode <<= 5;
-				GameGenieTable.TryGetValue(t, out var y);
+				_ = GameGenieTable.TryGetValue(t, out var y);
 				hexCode |= y;
 			}
 

src/BizHawk.Client.Common/cheats/NesGameGenieDecoder.cs

@@ -47,26 +47,26 @@ namespace BizHawk.Client.Common.cheats
 				result.Value = 0;
 				result.Address = 0x8000;
 
-				GameGenieTable.TryGetValue(code[0], out var x);
+				_ = GameGenieTable.TryGetValue(code[0], out var x);
 				result.Value |= x & 0x07;
 				result.Value |= (x & 0x08) << 4;
 
-				GameGenieTable.TryGetValue(code[1], out x);
+				_ = GameGenieTable.TryGetValue(code[1], out x);
 				result.Value |= (x & 0x07) << 4;
 				result.Address |= (x & 0x08) << 4;
 
-				GameGenieTable.TryGetValue(code[2], out x);
+				_ = GameGenieTable.TryGetValue(code[2], out x);
 				result.Address |= (x & 0x07) << 4;
 
-				GameGenieTable.TryGetValue(code[3], out x);
+				_ = GameGenieTable.TryGetValue(code[3], out x);
 				result.Address |= (x & 0x07) << 12;
 				result.Address |= x & 0x08;
 
-				GameGenieTable.TryGetValue(code[4], out x);
+				_ = GameGenieTable.TryGetValue(code[4], out x);
 				result.Address |= x & 0x07;
 				result.Address |= (x & 0x08) << 8;
 
-				GameGenieTable.TryGetValue(code[5], out x);
+				_ = GameGenieTable.TryGetValue(code[5], out x);
 				result.Address |= (x & 0x07) << 8;
 				result.Value |= x & 0x08;
 			}
@@ -79,34 +79,34 @@ namespace BizHawk.Client.Common.cheats
 				result.Address = 0x8000;
 				result.Compare = 0;
 
-				GameGenieTable.TryGetValue(code[0], out var x);
+				_ = GameGenieTable.TryGetValue(code[0], out var x);
 				result.Value |= x & 0x07;
 				result.Value |= (x & 0x08) << 4;
 
-				GameGenieTable.TryGetValue(code[1], out x);
+				_ = GameGenieTable.TryGetValue(code[1], out x);
 				result.Value |= (x & 0x07) << 4;
 				result.Address |= (x & 0x08) << 4;
 
-				GameGenieTable.TryGetValue(code[2], out x);
+				_ = GameGenieTable.TryGetValue(code[2], out x);
 				result.Address |= (x & 0x07) << 4;
 
-				GameGenieTable.TryGetValue(code[3], out x);
+				_ = GameGenieTable.TryGetValue(code[3], out x);
 				result.Address |= (x & 0x07) << 12;
 				result.Address |= x & 0x08;
 
-				GameGenieTable.TryGetValue(code[4], out x);
+				_ = GameGenieTable.TryGetValue(code[4], out x);
 				result.Address |= x & 0x07;
 				result.Address |= (x & 0x08) << 8;
 
-				GameGenieTable.TryGetValue(code[5], out x);
+				_ = GameGenieTable.TryGetValue(code[5], out x);
 				result.Address |= (x & 0x07) << 8;
 				result.Compare |= x & 0x08;
 
-				GameGenieTable.TryGetValue(code[6], out x);
+				_ = GameGenieTable.TryGetValue(code[6], out x);
 				result.Compare |= x & 0x07;
 				result.Compare |= (x & 0x08) << 4;
 
-				GameGenieTable.TryGetValue(code[7], out x);
+				_ = GameGenieTable.TryGetValue(code[7], out x);
 				result.Compare |= (x & 0x07) << 4;
 				result.Value |= x & 0x08;
 			}

src/BizHawk.Client.Common/cheats/SnesGameGenieDecoder.cs

@@ -55,53 +55,53 @@ namespace BizHawk.Client.Common.cheats
 			// Value
 			if (code.Length > 0)
 			{
-				SNESGameGenieTable.TryGetValue(code[0], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[0], out x);
 				result.Value = x << 4;
 			}
 
 			if (code.Length > 1)
 			{
-				SNESGameGenieTable.TryGetValue(code[1], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[1], out x);
 				result.Value |= x;
 			}
 
 			// Address
 			if (code.Length > 2)
 			{
-				SNESGameGenieTable.TryGetValue(code[2], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[2], out x);
 				result.Address = x << 12;
 			}
 
 			if (code.Length > 3)
 			{
-				SNESGameGenieTable.TryGetValue(code[3], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[3], out x);
 				result.Address |= x << 4;
 			}
 
 			if (code.Length > 4)
 			{
-				SNESGameGenieTable.TryGetValue(code[4], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[4], out x);
 				result.Address |= (x & 0xC) << 6;
 				result.Address |= (x & 0x3) << 22;
 			}
 
 			if (code.Length > 5)
 			{
-				SNESGameGenieTable.TryGetValue(code[5], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[5], out x);
 				result.Address |= (x & 0xC) << 18;
 				result.Address |= (x & 0x3) << 2;
 			}
 
 			if (code.Length > 6)
 			{
-				SNESGameGenieTable.TryGetValue(code[6], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[6], out x);
 				result.Address |= (x & 0xC) >> 2;
 				result.Address |= (x & 0x3) << 18;
 			}
 
 			if (code.Length > 7)
 			{
-				SNESGameGenieTable.TryGetValue(code[7], out x);
+				_ = SNESGameGenieTable.TryGetValue(code[7], out x);
 				result.Address |= (x & 0xC) << 14;
 				result.Address |= (x & 0x3) << 10;
 			}

src/BizHawk.Client.Common/config/ConfigExtensions.cs

@@ -45,7 +45,7 @@ namespace BizHawk.Client.Common
 		/// <returns>null if no settings were saved, or there was an error deserializing</returns>
 		public static object GetCoreSettings(this Config config, Type coreType, Type settingsType)
 		{
-			config.CoreSettings.TryGetValue(coreType.ToString(), out var j);
+			_ = config.CoreSettings.TryGetValue(coreType.ToString(), out var j);
 			return Deserialize(j, settingsType);
 		}
 
@@ -85,7 +85,7 @@ namespace BizHawk.Client.Common
 		/// <returns>null if no settings were saved, or there was an error deserializing</returns>
 		public static object GetCoreSyncSettings(this Config config, Type coreType, Type syncSettingsType)
 		{
-			config.CoreSyncSettings.TryGetValue(coreType.ToString(), out var j);
+			_ = config.CoreSyncSettings.TryGetValue(coreType.ToString(), out var j);
 			return Deserialize(j, syncSettingsType);
 		}
 

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -81,9 +81,9 @@ namespace BizHawk.Client.EmuHawk
 					entry.Click += ClickHandler;
 					return (ToolStripItem) entry;
 				}).ToArray());
-				submenu.DropDownOpened += (openedSender, _) =>
+				submenu.DropDownOpened += (openedSender, _1) =>
 				{
-					Config.PreferredCores.TryGetValue(groupLabel, out var preferred);
+					_ = Config.PreferredCores.TryGetValue(groupLabel, out var preferred);
 					foreach (ToolStripMenuItem entry in ((ToolStripMenuItem) openedSender).DropDownItems) entry.Checked = entry.Text == preferred;
 				};
 				CoresSubMenu.DropDownItems.Add(submenu);

src/BizHawk.Client.EmuHawk/config/ControllerConfig.cs

@@ -267,7 +267,7 @@ namespace BizHawk.Client.EmuHawk
 
 		private void SetControllerPicture(string controlName)
 		{
-			ControllerImages.TryGetValue(controlName, out var lazyBmp);
+			_ = ControllerImages.TryGetValue(controlName, out var lazyBmp);
 			if (lazyBmp != null)
 			{
 				var bmp = lazyBmp.Value;

src/BizHawk.Emulation.Common/Database/Database.cs

@@ -194,7 +194,7 @@ namespace BizHawk.Emulation.Common
 			_acquire.WaitOne();
 
 			var hashFormatted = FormatHash(hash);
-			DB.TryGetValue(hashFormatted, out var cgi);
+			_ = DB.TryGetValue(hashFormatted, out var cgi);
 			if (cgi == null)
 			{
 				Console.WriteLine($"DB: hash {hash} not in game database.");

src/BizHawk.Emulation.Cores/Consoles/Nintendo/SNES/LibsnesApi_QUERY.cs

@@ -29,7 +29,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES
 		public byte* QUERY_get_memory_data(SNES_MEMORY id)
 		{
 			string name = QUERY_MemoryNameForId(id);
-			_sharedMemoryBlocks.TryGetValue(name, out var ret);
+			_ = _sharedMemoryBlocks.TryGetValue(name, out var ret);
 			return (byte*)ret;
 		}
 

src/BizHawk.Emulation.Cores/CoreInventory.cs

@@ -151,7 +151,7 @@ namespace BizHawk.Emulation.Cores
 
 		public IEnumerable<Core> GetCores(string system)
 		{
-			_systems.TryGetValue(system, out var cores);
+			_ = _systems.TryGetValue(system, out var cores);
 			return cores ?? Enumerable.Empty<Core>();
 		}
 

src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Settings.cs

@@ -113,8 +113,8 @@ namespace BizHawk.Emulation.Cores.Waterbox
 				var possible = info.AllOverrides.Where(kvp => kvp.Value.NonSync && kvp.Value.NoRestart).Select(kvp => kvp.Key);
 				return possible.Where(key =>
 				{
-					x.MednafenValues.TryGetValue(key, out var xx);
-					y.MednafenValues.TryGetValue(key, out var yy);
+					_ = x.MednafenValues.TryGetValue(key, out var xx);
+					_ = y.MednafenValues.TryGetValue(key, out var yy);
 					return xx != yy;
 				});
 			}
@@ -124,8 +124,8 @@ namespace BizHawk.Emulation.Cores.Waterbox
 				var restarters = info.AllOverrides.Where(kvp => kvp.Value.NonSync && !kvp.Value.NoRestart).Select(kvp => kvp.Key);
 				foreach (var key in restarters)
 				{
-					x.MednafenValues.TryGetValue(key, out var xx);
-					y.MednafenValues.TryGetValue(key, out var yy);
+					_ = x.MednafenValues.TryGetValue(key, out var xx);
+					_ = y.MednafenValues.TryGetValue(key, out var yy);
 					if (xx != yy)
 						return PutSettingsDirtyBits.RebootCore;
 				}
@@ -186,8 +186,8 @@ namespace BizHawk.Emulation.Cores.Waterbox
 				var restarters = info.AllOverrides.Where(kvp => !kvp.Value.NonSync && !kvp.Value.NoRestart).Select(kvp => kvp.Key);
 				foreach (var key in restarters)
 				{
-					x.MednafenValues.TryGetValue(key, out var xx);
-					y.MednafenValues.TryGetValue(key, out var yy);
+					_ = x.MednafenValues.TryGetValue(key, out var xx);
+					_ = y.MednafenValues.TryGetValue(key, out var yy);
 					if (xx != yy)
 						return PutSettingsDirtyBits.RebootCore;
 				}
@@ -206,7 +206,7 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			{
 				// try to get actual value from settings
 				var dict = ovr.NonSync ? _settings.MednafenValues : _syncSettingsActual.MednafenValues;
-				dict.TryGetValue(name, out val);
+				_ = dict.TryGetValue(name, out val);
 			}
 			if (val == null)
 			{