Merge pull request dotnet#60855 from jasonmalinowski/provide-parse-op…

…tions-immediately

Provide parse options to the language service more quickly

src/Compilers/Core/MSBuildTask/Microsoft.CSharp.Core.targets

@@ -165,4 +165,26 @@
 
     <CallTarget Targets="$(TargetsTriggeredByCompilation)" Condition="'$(TargetsTriggeredByCompilation)' != ''" />
   </Target>
+
+  <!-- When we load a project in Visual Studio, the project system first does an evaluation pass of the
+       project, and hands the resulting list of <Compile> items to the language service. It then does an
+       execution pass executing CoreCompile passing SkipCompilerExecution=true and ProvideCommandLineArgs=true,
+       that resulting command line string is where we get our compiler switches. The execution pass is much
+       slower than the evaluation pass, so there's a window of time where we have a list of files, but not
+       any options yet.
+
+       Because there's a gap, that means there's a time where we are parsing source files with the default
+       parse options. We'll then have to reparse them a second time which isn't great. It also means any
+       cache lookups we do won't have the right options either, so the cache lookups might miss.
+
+       To help this, we'll have a property for the evaluation pass which is an "approximation" of the
+       options that would come out of CoreCompile, but only the ones that matter for parsing. It's acceptable
+       for this to be imperfect: once the execution pass is complete we'll use those options instead,
+       so any behaviors here that don't match the real command line generation will only be temporary, and
+       probably won't be any worse than having no options at all. -->
+
+  <PropertyGroup>
+    <CommandLineArgsForDesignTimeEvaluation>-langversion:$(LangVersion)</CommandLineArgsForDesignTimeEvaluation>
+    <CommandLineArgsForDesignTimeEvaluation Condition="'$(DefineConstants)' != ''">$(CommandLineArgsForDesignTimeEvaluation) -define:$(DefineConstants)</CommandLineArgsForDesignTimeEvaluation>
+  </PropertyGroup>
 </Project>

src/Compilers/Core/MSBuildTask/Microsoft.VisualBasic.Core.targets

@@ -134,4 +134,26 @@
 
     <CallTarget Targets="$(TargetsTriggeredByCompilation)" Condition="'$(TargetsTriggeredByCompilation)' != ''" />
   </Target>
+
+  <!-- When we load a project in Visual Studio, the project system first does an evaluation pass of the
+       project, and hands the resulting list of <Compile> items to the language service. It then does an
+       execution pass executing CoreCompile passing SkipCompilerExecution=true and ProvideCommandLineArgs=true,
+       that resulting command line string is where we get our compiler switches. The execution pass is much
+       slower than the evaluation pass, so there's a window of time where we have a list of files, but not
+       any options yet.
+
+       Because there's a gap, that means there's a time where we are parsing source files with the default
+       parse options. We'll then have to reparse them a second time which isn't great. It also means any
+       cache lookups we do won't have the right options either, so the cache lookups might miss.
+
+       To help this, we'll have a property for the evaluation pass which is an "approximation" of the
+       options that would come out of CoreCompile, but only the ones that matter for parsing. It's acceptable
+       for this to be imperfect: once the execution pass is complete we'll use those options instead,
+       so any behaviors here that don't match the real command line generation will only be temporary, and
+       probably won't be any worse than having no options at all. -->
+
+  <PropertyGroup>
+    <CommandLineArgsForDesignTimeEvaluation>-langversion:$(LangVersion)</CommandLineArgsForDesignTimeEvaluation>
+    <CommandLineArgsForDesignTimeEvaluation Condition="'$(FinalDefineConstants)' != ''">$(CommandLineArgsForDesignTimeEvaluation) -define:$(FinalDefineConstants)</CommandLineArgsForDesignTimeEvaluation>
+  </PropertyGroup>
 </Project>

src/VisualStudio/Core/Def/ProjectSystem/CPS/IWorkspaceProjectContext.cs

@@ -40,7 +40,6 @@ internal interface IWorkspaceProjectContext : IDisposable
 
         // Options.
 
-        [Obsolete("To avoid contributing to the large object heap, use SetOptions(ImmutableArray<string>). This API will be removed in the future.")]
         void SetOptions(string commandLineForOptions);
         void SetOptions(ImmutableArray<string> arguments);
 

src/VisualStudio/Core/Def/ProjectSystem/VisualStudioProjectOptionsProcessor.cs

@@ -86,7 +86,6 @@ private bool ReparseCommandLineIfChanged_NoLock(ImmutableArray<string> arguments
             return true;
         }
 
-        [Obsolete("To avoid contributing to the large object heap, use SetOptions(ImmutableArray<string>). This API will be removed in the future.")]
         public void SetCommandLine(string commandLine)
         {
             if (commandLine == null)

src/VisualStudio/Core/Impl/ProjectSystem/CPS/CPSProject_IWorkspaceProjectContext.cs

@@ -129,7 +129,6 @@ internal string? CompilationOutputAssemblyFilePath
 
         public ProjectId Id => _visualStudioProject.Id;
 
-        [Obsolete("To avoid contributing to the large object heap, use SetOptions(ImmutableArray<string>). This API will be removed in the future.")]
         public void SetOptions(string commandLineForOptions)
             => _visualStudioProjectOptionsProcessor?.SetCommandLine(commandLineForOptions);