Publish empty diagnostics on close (#4954)

Without this, diagnostics will linger after closing a file.

This refactors towards a pattern of putting outgoing calls as methods on
`Context`. I'm mixed on this, mainly thinking it's an improvement on
using `outgoing` directly (because it shares the name and structure),
might want to move it to a side-class later that is _only_ LSP wrappers.

I could also make inheritance private on OutgoingMessages and these
kinds of methods public there, but I'm hesitant to adopt that approach
versus a type separation.

toolchain/language_server/context.cpp

@@ -61,7 +61,9 @@ class PublishDiagnosticConsumer : public DiagnosticConsumer {
   }
 
   // Returns the constructed request.
-  auto params() -> llvm::json::Value { return params_; }
+  auto params() -> const clang::clangd::PublishDiagnosticsParams& {
+    return params_;
+  }
 
  private:
   // Returns the LSP range for a diagnostic. Note that Carbon uses 1-based
@@ -151,8 +153,7 @@ auto Context::File::SetText(Context& context, std::optional<int64_t> version,
   // Note we need to publish diagnostics even when empty.
   // TODO: Consider caching previously published diagnostics and only publishing
   // when they change.
-  context.outgoing().notify("textDocument/publishDiagnostics",
-                            consumer.params());
+  context.PublishDiagnostics(consumer.params());
 }
 
 auto Context::LookupFile(llvm::StringRef filename) -> File* {

toolchain/language_server/context.h

@@ -61,12 +61,15 @@ class Context {
   // null.
   auto LookupFile(llvm::StringRef filename) -> File*;
 
+  // Wrapper for LSP notification.
+  auto PublishDiagnostics(clang::clangd::PublishDiagnosticsParams params)
+      -> void {
+    outgoing_->notify("textDocument/publishDiagnostics", params);
+  }
+
   auto vlog_stream() -> llvm::raw_ostream* { return vlog_stream_; }
   auto file_emitter() -> FileDiagnosticEmitter& { return file_emitter_; }
   auto no_loc_emitter() -> NoLocDiagnosticEmitter& { return no_loc_emitter_; }
-  auto outgoing() -> clang::clangd::LSPBinder::RawOutgoing& {
-    return *outgoing_;
-  }
 
   auto files() -> Map<std::string, File>& { return files_; }
 

toolchain/language_server/handle_text_document.cpp

@@ -58,7 +58,11 @@ auto HandleDidCloseTextDocument(
     return;
   }
 
-  if (!context.files().Erase(filename)) {
+  if (context.files().Erase(filename)) {
+    // Clear diagnostics when the document closes. Otherwise, any diagnostics
+    // will linger.
+    context.PublishDiagnostics({.uri = params.textDocument.uri});
+  } else {
     CARBON_DIAGNOSTIC(LanguageServerCloseUnknownFile, Warning,
                       "tried closing unknown file; ignoring request");
     context.file_emitter().Emit(filename, LanguageServerCloseUnknownFile);

toolchain/language_server/testdata/text_document/diagnostics.carbon

@@ -119,6 +119,15 @@
 // CHECK:STDOUT:     "uri": "file:///test.carbon",
 // CHECK:STDOUT:     "version": 2
 // CHECK:STDOUT:   }
+// CHECK:STDOUT: }Content-Length: 144{{\r}}
+// CHECK:STDOUT: {{\r}}
+// CHECK:STDOUT: {
+// CHECK:STDOUT:   "jsonrpc": "2.0",
+// CHECK:STDOUT:   "method": "textDocument/publishDiagnostics",
+// CHECK:STDOUT:   "params": {
+// CHECK:STDOUT:     "diagnostics": [],
+// CHECK:STDOUT:     "uri": "file:///test.carbon"
+// CHECK:STDOUT:   }
 // CHECK:STDOUT: }Content-Length: 51{{\r}}
 // CHECK:STDOUT: {{\r}}
 // CHECK:STDOUT: {

toolchain/language_server/testdata/text_document/open_change_close.carbon

@@ -55,6 +55,15 @@
 // CHECK:STDOUT:     "diagnostics": [],
 // CHECK:STDOUT:     "uri": "file:///test.carbon"
 // CHECK:STDOUT:   }
+// CHECK:STDOUT: }Content-Length: 144{{\r}}
+// CHECK:STDOUT: {{\r}}
+// CHECK:STDOUT: {
+// CHECK:STDOUT:   "jsonrpc": "2.0",
+// CHECK:STDOUT:   "method": "textDocument/publishDiagnostics",
+// CHECK:STDOUT:   "params": {
+// CHECK:STDOUT:     "diagnostics": [],
+// CHECK:STDOUT:     "uri": "file:///test.carbon"
+// CHECK:STDOUT:   }
 // CHECK:STDOUT: }Content-Length: 51{{\r}}
 // CHECK:STDOUT: {{\r}}
 // CHECK:STDOUT: {