Method not found: 'System.ReadOnlySpan`1<Char> Microsoft.IO.Path.GetFileName(System.ReadOnlySpan`1<Char>)'

[mwaaas]

Failing to load project on vscode with the following error

System.MissingMethodException: Method not found: 'System.ReadOnlySpan1<Char> Microsoft.IO.Path.GetFileName(System.ReadOnlySpan1)'.
at Microsoft.Build.Shared.FileMatcher.IsFileNameMatch(String path, String pattern)
at System.Linq.Enumerable.WhereArrayIterator1.MoveNext() at System.Linq.Buffer1..ctor(IEnumerable1 source) at System.Linq.Enumerable.ToArray[TSource](IEnumerable1 source)
at Microsoft.Build.Shared.FileMatcher.GetFilesForStep(RecursiveStepResult stepResult, RecursionState recursionState, String projectDirectory, Boolean stripProjectDirectory)
at Microsoft.Build.Shared.FileMatcher.GetFilesRecursive(ConcurrentStack1 listOfFiles, RecursionState recursionState, String projectDirectory, Boolean stripProjectDirectory, IList1 searchesToExclude, Dictionary2 searchesToExcludeInSubdirs, TaskOptions taskOptions) at Microsoft.Build.Shared.FileMatcher.GetFilesImplementation(String projectDirectoryUnescaped, String filespecUnescaped, List1 excludeSpecsUnescaped)
at Microsoft.Build.Shared.FileMatcher.<>c__DisplayClass67_0.b__1(String _)
at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory)
at Microsoft.Build.Shared.FileMatcher.GetFiles(String projectDirectoryUnescaped, String filespecUnescaped, List1 excludeSpecsUnescaped) at Microsoft.Build.Internal.EngineFileUtilities.GetFileList(String directoryEscaped, String filespecEscaped, Boolean returnEscaped, Boolean forceEvaluateWildCards, IEnumerable1 excludeSpecsEscaped, FileMatcher fileMatcher, Object loggingMechanism, IElementLocation includeLocation, IElementLocation excludeLocation, IElementLocation importLocation, BuildEventContext buildEventContext, String buildEventFileInfoFullPath, Boolean disableExcludeDriveEnumerationWarning)
at Microsoft.Build.Internal.EngineFileUtilities.GetFileListEscaped(String directoryEscaped, String filespecEscaped, IEnumerable1 excludeSpecsEscaped, Boolean forceEvaluate, FileMatcher fileMatcher, Object loggingMechanism, IElementLocation includeLocation, IElementLocation excludeLocation, IElementLocation importLocation, BuildEventContext buildEventContext, String buildEventFileInfoFullPath, Boolean disableExcludeDriveEnumerationWarning) at Microsoft.Build.Evaluation.Evaluator4.ExpandAndLoadImportsFromUnescapedImportExpression(String directoryOfImportingFile, ProjectImportElement importElement, String unescapedExpression, Boolean throwOnFileNotExistsError, List1& imports) at Microsoft.Build.Evaluation.Evaluator4.ExpandAndLoadImportsFromUnescapedImportExpressionConditioned(String directoryOfImportingFile, ProjectImportElement importElement, List1& projects, SdkResult& sdkResult, Boolean throwOnFileNotExistsError) at Microsoft.Build.Evaluation.Evaluator4.ExpandAndLoadImports(String directoryOfImportingFile, ProjectImportElement importElement, SdkResult& sdkResult)
at Microsoft.Build.Evaluation.Evaluator4.EvaluateImportElement(String directoryOfImportingFile, ProjectImportElement importElement) at Microsoft.Build.Evaluation.Evaluator4.PerformDepthFirstPass(ProjectRootElement currentProjectOrImport)
at Microsoft.Build.Evaluation.Evaluator4.EvaluateImportElement(String directoryOfImportingFile, ProjectImportElement importElement) at Microsoft.Build.Evaluation.Evaluator4.PerformDepthFirstPass(ProjectRootElement currentProjectOrImport)
at Microsoft.Build.Evaluation.Evaluator4.EvaluateImportElement(String directoryOfImportingFile, ProjectImportElement importElement) at Microsoft.Build.Evaluation.Evaluator4.PerformDepthFirstPass(ProjectRootElement currentProjectOrImport)
at Microsoft.Build.Evaluation.Evaluator4.Evaluate() at Microsoft.Build.Evaluation.Evaluator4.Evaluate(IEvaluatorData4 data, Project project, ProjectRootElement root, ProjectLoadSettings loadSettings, Int32 maxNodeCount, PropertyDictionary1 environmentProperties, ILoggingService loggingService, IItemFactory2 itemFactory, IToolsetProvider toolsetProvider, ProjectRootElementCacheBase projectRootElementCache, BuildEventContext buildEventContext, ISdkResolverService sdkResolverService, Int32 submissionId, EvaluationContext evaluationContext, Boolean interactive) at Microsoft.Build.Evaluation.Project.ProjectImpl.Reevaluate(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext) at Microsoft.Build.Evaluation.Project.ProjectImpl.ReevaluateIfNecessary(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext) at Microsoft.Build.Evaluation.Project.ProjectImpl.ReevaluateIfNecessary(EvaluationContext evaluationContext) at Microsoft.Build.Evaluation.Project.ProjectImpl.Initialize(IDictionary2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext)
at Microsoft.Build.Evaluation.Project..ctor(String projectFile, IDictionary2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectCollection projectCollection, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext, IDirectoryCacheFactory directoryCacheFactory) at Microsoft.Build.Evaluation.ProjectCollection.LoadProject(String fileName, IDictionary2 globalProperties, String toolsVersion)
at OmniSharp.MSBuild.ProjectLoader.EvaluateProjectFileCore(String filePath, IReadOnlyDictionary2 projectConfigurationsInSolution, IList1 loggers) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectLoader.cs:line 160
at OmniSharp.MSBuild.ProjectLoader.BuildProject(String filePath, IReadOnlyDictionary2 configurationsInSolution) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectLoader.cs:line 84 at OmniSharp.MSBuild.ProjectFile.ProjectFileInfo.Load(String filePath, ProjectIdInfo projectIdInfo, ProjectLoader loader, Guid sessionId, DotNetInfo dotNetInfo) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectFile\ProjectFileInfo.cs:line 117 at OmniSharp.MSBuild.ProjectManager.<>c__DisplayClass32_0.<LoadProject>b__0() in D:\a\1\s\src\OmniSharp.MSBuild\ProjectManager.cs:line 305 at OmniSharp.MSBuild.ProjectManager.LoadOrReloadProject(String projectFilePath, Func1 loader) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectManager.cs:line 316

[mwaaas]

This did resolve this by changing omnisharp.json to use a different build.

The project was not using Visual studio build but a custom one and omnisharp were using visual studio build.

By adding omnisharp.json to the root of the project with the specific build I wanted it to fix my issue.

https://gist.github.com/mwaaas/dc80ac3d9e8a6abe2759c9e605120706