Support returning non-hierarchical symbols

If `hierarchicalDocumentSymbolSupport` is not true in the client capabilites
then it does not support the `DocumentSymbol[]` return type from the
`textDocument/documentSymbol` request and we must fall back to `SymbolInformation[]`.

This is one of the few requests that use the client capabilities to
differentiate between return types and could cause problems for clients.

See microsoft/language-server-protocol#538 (comment) for more context.

Found while looking at #144

crates/rust-analyzer/src/config.rs

@@ -69,6 +69,7 @@ pub enum RustfmtConfig {
 pub struct ClientCapsConfig {
     pub location_link: bool,
     pub line_folding_only: bool,
+    pub hierarchical_symbols: bool,
 }
 
 impl Default for Config {
@@ -214,5 +215,10 @@ impl Config {
         if let Some(value) = caps.folding_range.as_ref().and_then(|it| it.line_folding_only) {
             self.client_caps.line_folding_only = value
         }
+        if let Some(value) =
+            caps.document_symbol.as_ref().and_then(|it| it.hierarchical_document_symbol_support)
+        {
+            self.client_caps.hierarchical_symbols = value
+        }
     }
 }

crates/rust-analyzer/src/conv.rs

@@ -2,17 +2,18 @@
 //! and LSP types.
 
 use lsp_types::{
-    self, CreateFile, DiagnosticSeverity, DocumentChangeOperation, DocumentChanges, Documentation,
-    Location, LocationLink, MarkupContent, MarkupKind, ParameterInformation, ParameterLabel,
-    Position, Range, RenameFile, ResourceOp, SemanticTokenModifier, SemanticTokenType,
-    SignatureInformation, SymbolKind, TextDocumentEdit, TextDocumentIdentifier, TextDocumentItem,
-    TextDocumentPositionParams, Url, VersionedTextDocumentIdentifier, WorkspaceEdit,
+    self, CreateFile, DiagnosticSeverity, DocumentChangeOperation, DocumentChanges, DocumentSymbol,
+    Documentation, Location, LocationLink, MarkupContent, MarkupKind, ParameterInformation,
+    ParameterLabel, Position, Range, RenameFile, ResourceOp, SemanticTokenModifier,
+    SemanticTokenType, SignatureInformation, SymbolInformation, SymbolKind, TextDocumentEdit,
+    TextDocumentIdentifier, TextDocumentItem, TextDocumentPositionParams, Url,
+    VersionedTextDocumentIdentifier, WorkspaceEdit,
 };
 use ra_ide::{
     translate_offset_with_edit, CompletionItem, CompletionItemKind, CompletionScore, FileId,
     FilePosition, FileRange, FileSystemEdit, Fold, FoldKind, Highlight, HighlightModifier,
     HighlightTag, InlayHint, InlayKind, InsertTextFormat, LineCol, LineIndex, NavigationTarget,
-    RangeInfo, ReferenceAccess, Severity, SourceChange, SourceFileEdit,
+    RangeInfo, ReferenceAccess, Severity, SourceChange, SourceFileEdit, StructureNode,
 };
 use ra_syntax::{SyntaxKind, TextRange, TextUnit};
 use ra_text_edit::{AtomTextEdit, TextEdit};
@@ -334,6 +335,75 @@ impl ConvWith<&FoldConvCtx<'_>> for Fold {
     }
 }
 
+impl ConvWith<(&FileId, &WorldSnapshot, &LineIndex)> for Vec<StructureNode> {
+    type Output = lsp_types::DocumentSymbolResponse;
+
+    fn conv_with(self, ctx: (&FileId, &WorldSnapshot, &LineIndex)) -> Self::Output {
+        let file_id = ctx.0;
+        let world = ctx.1;
+        let line_index = ctx.2;
+        let supports_hierarchy = world.config.client_caps.hierarchical_symbols;
+
+        if supports_hierarchy {
+            let mut parents: Vec<(DocumentSymbol, Option<usize>)> = Vec::new();
+
+            for symbol in self.into_iter() {
+                let doc_symbol = DocumentSymbol {
+                    name: symbol.label,
+                    detail: symbol.detail,
+                    kind: symbol.kind.conv(),
+                    deprecated: Some(symbol.deprecated),
+                    range: symbol.node_range.conv_with(line_index),
+                    selection_range: symbol.navigation_range.conv_with(line_index),
+                    children: None,
+                };
+                parents.push((doc_symbol, symbol.parent));
+            }
+            let mut res = Vec::new();
+            while let Some((node, parent)) = parents.pop() {
+                match parent {
+                    None => res.push(node),
+                    Some(i) => {
+                        let children = &mut parents[i].0.children;
+                        if children.is_none() {
+                            *children = Some(Vec::new());
+                        }
+                        children.as_mut().unwrap().push(node);
+                    }
+                }
+            }
+            res.into()
+        } else {
+            let mut parents: Vec<(SymbolInformation, Option<usize>)> = Vec::new();
+            for symbol in self.into_iter() {
+                parents.push((
+                    SymbolInformation {
+                        name: symbol.label,
+                        kind: symbol.kind.conv(),
+                        deprecated: Some(symbol.deprecated),
+                        location: to_location(*file_id, symbol.navigation_range, world, line_index)
+                            .unwrap(),
+                        container_name: None,
+                    },
+                    symbol.parent,
+                ))
+            }
+            let mut res = Vec::new();
+            while let Some((mut node, parent)) = parents.pop() {
+                match parent {
+                    None => res.push(node),
+                    Some(i) => {
+                        node.container_name = Some(parents[i].0.name.clone());
+                        res.push(node)
+                    }
+                }
+            }
+
+            res.into()
+        }
+    }
+}
+
 impl ConvWith<&LineIndex> for InlayHint {
     type Output = req::InlayHint;
     fn conv_with(self, line_index: &LineIndex) -> Self::Output {

crates/rust-analyzer/src/main_loop/handlers.rs

@@ -12,11 +12,10 @@ use lsp_types::{
     CallHierarchyIncomingCall, CallHierarchyIncomingCallsParams, CallHierarchyItem,
     CallHierarchyOutgoingCall, CallHierarchyOutgoingCallsParams, CallHierarchyPrepareParams,
     CodeAction, CodeActionResponse, CodeLens, Command, CompletionItem, Diagnostic,
-    DocumentFormattingParams, DocumentHighlight, DocumentSymbol, FoldingRange, FoldingRangeParams,
-    Hover, HoverContents, Location, MarkupContent, MarkupKind, Position, PrepareRenameResponse,
-    Range, RenameParams, SemanticTokensParams, SemanticTokensRangeParams,
-    SemanticTokensRangeResult, SemanticTokensResult, SymbolInformation, TextDocumentIdentifier,
-    TextEdit, WorkspaceEdit,
+    DocumentFormattingParams, DocumentHighlight, FoldingRange, FoldingRangeParams, Hover,
+    HoverContents, Location, MarkupContent, MarkupKind, Position, PrepareRenameResponse, Range,
+    RenameParams, SemanticTokensParams, SemanticTokensRangeParams, SemanticTokensRangeResult,
+    SemanticTokensResult, SymbolInformation, TextDocumentIdentifier, TextEdit, WorkspaceEdit,
 };
 use ra_ide::{
     Assist, AssistId, FileId, FilePosition, FileRange, Query, RangeInfo, Runnable, RunnableKind,
@@ -220,35 +219,7 @@ pub fn handle_document_symbol(
     let file_id = params.text_document.try_conv_with(&world)?;
     let line_index = world.analysis().file_line_index(file_id)?;
 
-    let mut parents: Vec<(DocumentSymbol, Option<usize>)> = Vec::new();
-
-    for symbol in world.analysis().file_structure(file_id)? {
-        let doc_symbol = DocumentSymbol {
-            name: symbol.label,
-            detail: symbol.detail,
-            kind: symbol.kind.conv(),
-            deprecated: Some(symbol.deprecated),
-            range: symbol.node_range.conv_with(&line_index),
-            selection_range: symbol.navigation_range.conv_with(&line_index),
-            children: None,
-        };
-        parents.push((doc_symbol, symbol.parent));
-    }
-    let mut res = Vec::new();
-    while let Some((node, parent)) = parents.pop() {
-        match parent {
-            None => res.push(node),
-            Some(i) => {
-                let children = &mut parents[i].0.children;
-                if children.is_none() {
-                    *children = Some(Vec::new());
-                }
-                children.as_mut().unwrap().push(node);
-            }
-        }
-    }
-
-    Ok(Some(res.into()))
+    Ok(Some(world.analysis().file_structure(file_id)?.conv_with((&file_id, &world, &line_index))))
 }
 
 pub fn handle_workspace_symbol(