false warning from rust-analyzer about "Failed to load workspaces" when linkedProjects is set

[ksqsf]

I'm using Emacs with Eglot as its LSP client. My project structure is fairly complex:

+ project/
  + src/
  + include/
  + plugins/
    + rust/
      + Cargo.toml   workspace
      + crate1/
      + crate2/
      + ...

I set rust-analyzer.linkedProjects through .dir-locals.el

((nil . ((eglot-workspace-configuration . (:rust-analyzer (:linkedProjects ["$PROJECT/plugins/rust/Cargo.toml"]))))))

This works well: I have perfectly working completion and inlay hints and others. But the problem is: whenever I start the lsp client, there will be a false warning:

[eglot] Server reports (type=1): Failed to load workspaces.`rust-analyzer.linkedProjects` have been specified, which may be incorrect. Specified project paths:
    $PROJECT/plugins/rust/Cargo.toml

This is quite annoying and misleading if it actually works. And I'm baffled why rust-analyzer complains this when it actually knows the path.

VSCode does not report this warning, so I reported this to Eglot first, and one of the Eglot contributors suggested that Eglot is unlikely to be incorrect here, so I forwarded the issue here.

Eglot debug logs (until the error message):

[jsonrpc] D[12:06:54.935] Running language server: rust-analyzer
[jsonrpc] e[12:06:54.935] --> initialize[1] {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"processId":1596439,"clientInfo":{"name":"Eglot","version":"1.17.30"},"rootPath":"$PROJECT/","rootUri":"file://$PROJECT","initializationOptions":{},"capabilities":{"workspace":{"applyEdit":true,"executeCommand":{"dynamicRegistration":false},"workspaceEdit":{"documentChanges":true},"didChangeWatchedFiles":{"dynamicRegistration":true},"symbol":{"dynamicRegistration":false},"configuration":true,"workspaceFolders":true},"textDocument":{"synchronization":{"dynamicRegistration":false,"willSave":true,"willSaveWaitUntil":true,"didSave":true},"completion":{"dynamicRegistration":false,"completionItem":{"snippetSupport":true,"deprecatedSupport":true,"resolveSupport":{"properties":["documentation","details","additionalTextEdits"]},"tagSupport":{"valueSet":[1]}},"contextSupport":true},"hover":{"dynamicRegistration":false,"contentFormat":["markdown","plaintext"]},"signatureHelp":{"dynamicRegistration":false,"signatureInformation":{"parameterInformation":{"labelOffsetSupport":true},"documentationFormat":["markdown","plaintext"],"activeParameterSupport":true}},"references":{"dynamicRegistration":false},"definition":{"dynamicRegistration":false,"linkSupport":true},"declaration":{"dynamicRegistration":false,"linkSupport":true},"implementation":{"dynamicRegistration":false,"linkSupport":true},"typeDefinition":{"dynamicRegistration":false,"linkSupport":true},"documentSymbol":{"dynamicRegistration":false,"hierarchicalDocumentSymbolSupport":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]}},"documentHighlight":{"dynamicRegistration":false},"codeAction":{"dynamicRegistration":false,"resolveSupport":{"properties":["edit","command"]},"dataSupport":true,"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}},"isPreferredSupport":true},"formatting":{"dynamicRegistration":false},"rangeFormatting":{"dynamicRegistration":false},"rename":{"dynamicRegistration":false},"inlayHint":{"dynamicRegistration":false},"publishDiagnostics":{"relatedInformation":false,"codeDescriptionSupport":false,"tagSupport":{"valueSet":[1,2]}}},"window":{"showDocument":{"support":true},"workDoneProgress":true},"general":{"positionEncodings":["utf-32","utf-8","utf-16"]},"experimental":{}},"workspaceFolders":[{"uri":"file://$PROJECT","name":"$PROJECT/"}]}}
[jsonrpc] e[12:06:54.972] <-- initialize[1] {"jsonrpc":"2.0","id":1,"result":{"capabilities":{"positionEncoding":"utf-32","textDocumentSync":{"openClose":true,"change":2,"save":{}},"selectionRangeProvider":true,"hoverProvider":true,"completionProvider":{"resolveProvider":true,"triggerCharacters":[":",".","'","("],"completionItem":{"labelDetailsSupport":false}},"signatureHelpProvider":{"triggerCharacters":["(",",","<"]},"definitionProvider":true,"typeDefinitionProvider":true,"implementationProvider":true,"referencesProvider":true,"documentHighlightProvider":true,"documentSymbolProvider":true,"workspaceSymbolProvider":true,"codeActionProvider":{"codeActionKinds":["","quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite"],"resolveProvider":true},"codeLensProvider":{"resolveProvider":true},"documentFormattingProvider":true,"documentRangeFormattingProvider":false,"documentOnTypeFormattingProvider":{"firstTriggerCharacter":"=","moreTriggerCharacter":[".",">","{","("]},"renameProvider":{"prepareProvider":true},"foldingRangeProvider":true,"declarationProvider":true,"workspace":{"workspaceFolders":{"supported":true,"changeNotifications":true},"fileOperations":{"willRename":{"filters":[{"scheme":"file","pattern":{"glob":"**/*.rs","matches":"file"}},{"scheme":"file","pattern":{"glob":"**","matches":"folder"}}]}}},"callHierarchyProvider":true,"semanticTokensProvider":{"legend":{"tokenTypes":["comment","decorator","enumMember","enum","function","interface","keyword","macro","method","namespace","number","operator","parameter","property","string","struct","typeParameter","variable","angle","arithmetic","attributeBracket","attribute","bitwise","boolean","brace","bracket","builtinAttribute","builtinType","character","colon","comma","comparison","constParameter","const","deriveHelper","derive","dot","escapeSequence","formatSpecifier","generic","invalidEscapeSequence","label","lifetime","logical","macroBang","parenthesis","procMacro","punctuation","selfKeyword","selfTypeKeyword","semicolon","static","toolModule","typeAlias","union","unresolvedReference"],"tokenModifiers":["async","documentation","declaration","static","defaultLibrary","associated","attribute","callable","constant","consuming","controlFlow","crateRoot","injected","intraDocLink","library","macro","mutable","procMacro","public","reference","trait","unsafe"]},"range":true,"full":{"delta":true}},"inlayHintProvider":{"resolveProvider":true},"diagnosticProvider":{"interFileDependencies":true,"workspaceDiagnostics":false},"experimental":{"externalDocs":true,"hoverRange":true,"joinLines":true,"matchingBrace":true,"moveItem":true,"onEnter":true,"openCargoToml":true,"parentModule":true,"runnables":{"kinds":["cargo"]},"ssr":true,"workspaceSymbolScopeKindFiltering":true}},"serverInfo":{"name":"rust-analyzer","version":"1.84.0 (9fc6b43 2025-01-07)"}}}
[jsonrpc] e[12:06:54.972] --> initialized {"jsonrpc":"2.0","method":"initialized","params":{}}
[jsonrpc] e[12:06:54.973] --> textDocument/didOpen {"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"file://$PROJECT/plugins/rust/lib/rinflex/src/rec_inflex.rs","version":0,"languageId":"rust","text":"$SKIPPED"}}}
[jsonrpc] e[12:06:54.974] --> workspace/didChangeConfiguration {"jsonrpc":"2.0","method":"workspace/didChangeConfiguration","params":{"settings":{"rust-analyzer":{"linkedProjects":["$PROJECT/plugins/rust/Cargo.toml"]}}}}
[stderr]  2025-04-10T12:06:54.973365031+02:00 ERROR failed to find any projects in [AbsPathBuf("$PROJECT")]
[stderr]  2025-04-10T12:06:54.976596661+02:00 ERROR FetchWorkspaceError: rust-analyzer failed to fetch workspace
[stderr]  2025-04-10T12:06:54.97695733+02:00 ERROR FetchWorkspaceError: rust-analyzer failed to fetch workspace
[jsonrpc] e[12:06:54.984] <-- window/showMessage {"jsonrpc":"2.0","method":"window/showMessage","params":{"type":2,"message":"Failed to discover workspace.\nConsider adding the `Cargo.toml` of the workspace to the [`linkedProjects`](https://rust-analyzer.github.io/manual.html#rust-analyzer.linkedProjects) setting."}}

The problem can be reproduced with the latest nightly version rust-analyzer 1.88.0-nightly (934880f 2025-04-09) as well.

edit: $PROJECT are not really envvars here. I used them to make the paths more clear.

[davidbarsky]

The response here nailed the problem. rust-analyzer-the-language-server will not do shell/env expansion of variables like $PROJECT; it considers the string literally. rust-analyzer’s VS Code extension will for items like a ~.

What’s happening here is that rust-analyzer first scans child directories for Cargo.toml(s), successfully finds one, and loads your project. It then looks for a file whose absolute or relative path is literally $PROJECT/plugins/rust/Cargo.toml, fails to find one, and reports the error that you see.

[ksqsf]

Sorry, I didn't specify it clearly enough. The real paths are absolute paths, and I replaced them by $PROJECT in the issue for clarity. I will edit to add this to the issue.

What’s happening here is that rust-analyzer first scans child directories for Cargo.toml(s), successfully finds one, and loads your project. It then looks for a file whose absolute or relative path is literally $PROJECT/plugins/rust/Cargo.toml, fails to find one, and reports the error that you see.

My understanding is that rust-analyzer will scan recursively for Cargo.toml regardless of any settings, and then selects only those in linkedProjects. (But it should have found it because rust-analyzer works for me.)

Does this mean that rust-analyzer currently doesn't really have a way to "select a folder NOT at the top-level directory", and linkedProjects is just a workaround in this case?

[snprajwal]

Is your project nested more than one level deep? rust-analyzer currently searches for Cargo.toml in the active dir and all subdirs, but does not recursively search past that (this is to prevent the search space from growing exponentially for larger projects).

[ksqsf]

@snprajwal Yes, it's under /plugins/rust.