GH4471: Improve script cache hash generation algorithm

src/Cake.Tests/Infrastructure/Scripting/RoslynScriptSessionTests.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Collections.Generic;
+using Cake.Core.Configuration;
+using Cake.Core.Diagnostics;
+using Cake.Core.Reflection;
+using Cake.Core.Scripting;
+using Cake.Infrastructure;
+using Cake.Infrastructure.Scripting;
+using NSubstitute;
+using Xunit;
+
+namespace Cake.Tests.Infrastructure.Scripting
+{
+    public sealed partial class RoslynScriptSessionTests
+    {
+        [Fact]
+        public void Generates_Equal_Hash_For_Different_Directories_Equal_Files()
+        {
+            var hashes = new HashSet<string>();
+            var directories = new[]
+            {
+                "c:/source/test1",
+                "c:/source/test2",
+                "c:/source/test3"
+            };
+
+            foreach (var directory in directories)
+            {
+                var scriptHost = Substitute.For<IScriptHost>();
+                scriptHost.Context.Environment.WorkingDirectory.Returns(directory);
+
+                var assemblyLoader = Substitute.For<IAssemblyLoader>();
+                var cakeConfiguration = Substitute.For<ICakeConfiguration>();
+                var cakeLog = Substitute.For<ICakeLog>();
+
+                var scriptHostSettings = Substitute.For<IScriptHostSettings>();
+                scriptHostSettings.Script.Returns(new Core.IO.FilePath($"{directory}/build.cake"));
+
+                var scriptEngine = new RoslynScriptSession(scriptHost, assemblyLoader,
+                    cakeConfiguration, cakeLog, scriptHostSettings);
+
+                var script = GenerateScript(directory);
+
+                var hash = scriptEngine.GetScriptHash(script);
+                hashes.Add(hash);
+            }
+
+            Assert.Single(hashes);
+        }
+
+        [Fact]
+        public void Generates_Different_Hash_For_Equal_Directories_Different_Files()
+        {
+            var hashes = new HashSet<string>();
+
+            var directory = "c:/source/test1";
+
+            var randomLines = new[]
+            {
+                "random 1",
+                "random 2",
+                "random 3"
+            };
+
+            foreach (var randomLine in randomLines)
+            {
+                var scriptHost = Substitute.For<IScriptHost>();
+                scriptHost.Context.Environment.WorkingDirectory.Returns(directory);
+
+                var assemblyLoader = Substitute.For<IAssemblyLoader>();
+                var cakeConfiguration = Substitute.For<ICakeConfiguration>();
+                var cakeLog = Substitute.For<ICakeLog>();
+
+                var scriptHostSettings = Substitute.For<IScriptHostSettings>();
+                scriptHostSettings.Script.Returns(new Core.IO.FilePath($"{directory}/build.cake"));
+
+                var scriptEngine = new RoslynScriptSession(scriptHost, assemblyLoader,
+                    cakeConfiguration, cakeLog, scriptHostSettings);
+
+                var script = GenerateScript(directory, new[]
+                {
+                    randomLine
+                });
+
+                var hash = scriptEngine.GetScriptHash(script);
+                hashes.Add(hash);
+            }
+
+            Assert.Equal(randomLines.Length, hashes.Count);
+        }
+
+        private Script GenerateScript(string path, IReadOnlyList<string> additionalLines = null)
+        {
+            var lines = new List<string>
+            {
+                $"#line 1 \"{path}/build.cake\"",
+                "var x = 1;",
+                "var y = 2;",
+                "var z = x + y;"
+            };
+
+            if (additionalLines is not null)
+            {
+                lines.AddRange(additionalLines);
+            }
+
+            var script = new Script(Array.Empty<string>(), lines,
+                Array.Empty<ScriptAlias>(), Array.Empty<string>(), Array.Empty<string>(),
+                Array.Empty<string>());
+
+            return script;
+        }
+    }
+}

src/Cake/Infrastructure/Scripting/RoslynScriptSession.cs

@@ -213,9 +213,21 @@ private FilePath GetCachedAssemblyPath(Script script, FilePath scriptName)
                     '.',
                     scriptName.GetFilenameWithoutExtension().FullPath,
                     _host.GetType().Name,
-                    FastHash.GenerateHash(Encoding.UTF8.GetBytes(string.Concat(script.Lines))),
+                    GetScriptHash(script),
                     "dll"));
 
+        public string GetScriptHash(Script script)
+        {
+            // Remove specific lines that could cause the same files to generate different
+            // hashes. See https://github.com/cake-build/cake/issues/4471 for more information
+            var linesToHash = script.Lines
+                .Where(line => !line.StartsWith("#line ", StringComparison.OrdinalIgnoreCase))
+                .ToArray();
+
+            var hash = FastHash.GenerateHash(Encoding.UTF8.GetBytes(string.Concat(linesToHash)));
+            return hash;
+        }
+
         private void RunScriptAssembly(string assemblyPath)
         {
             var assembly = _loader.Load(assemblyPath, false);