Add tags to diagnostics

Also removes the diagnostic.Data from the new diagnostics, which AFAICS
is unused; we can save ourselves the json marshaling.

As a part of this, added a first pass at adding tests for diagnostics;
we don't currently have any. These are a bit different because we
haven't implemented [PullDiagnostics][1] (we can add this, but we'd need
a custom implementation, or wait until [go.lsp.dev upgrades to
3.17][2]). Instead, we intercept the notifications from the
server. Lastly, since we don't actually want the tests to wait around,
adds synctest and only runs the tests on Go 1.25 for now (1.26 should be
released next month and we'll be able to upgrade to 1.25 as our
minimum).

This is in preparation to eventually landing relatedInformation (other
spans) in diagnostics, from bufbuild/protocompile#659.

Also pulls in the latest protocompile@main to bring in the new
deprecated tag.

[1]: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_pullDiagnostics
[2]: go-language-server/protocol#52

Author: stefanvanburen

go.mod

@@ -16,7 +16,7 @@ require (
 	buf.build/go/standard v0.1.0
 	connectrpc.com/connect v1.19.1
 	connectrpc.com/otelconnect v0.9.0
-	github.com/bufbuild/protocompile v0.14.2-0.20260121154354-91940cd2bca3
+	github.com/bufbuild/protocompile v0.14.2-0.20260130195850-5c64bed4577e
 	github.com/bufbuild/protoplugin v0.0.0-20250218205857-750e09ce93e1
 	github.com/cli/browser v1.3.0
 	github.com/docker/docker v28.5.2+incompatible

go.sum

@@ -40,10 +40,13 @@ github.com/antlr4-go/antlr/v4 v4.13.1 h1:SqQKkuVZ+zWkMMNkjy5FZe5mr5WURWnlpmOuzYW
 github.com/antlr4-go/antlr/v4 v4.13.1/go.mod h1:GKmUxMtwp6ZgGwZSva4eWPC5mS6vUAmOABFgjdkM7Nw=
 github.com/bmatcuk/doublestar/v4 v4.9.2 h1:b0mc6WyRSYLjzofB2v/0cuDUZ+MqoGyH3r0dVij35GI=
 github.com/bmatcuk/doublestar/v4 v4.9.2/go.mod h1:xBQ8jztBU6kakFMg+8WGxn0c6z1fTSPVIjEY1Wr7jzc=
+github.com/bmatcuk/doublestar/v4 v4.10.0 h1:zU9WiOla1YA122oLM6i4EXvGW62DvKZVxIe6TYWexEs=
 github.com/brianvoe/gofakeit/v6 v6.28.0 h1:Xib46XXuQfmlLS2EXRuJpqcw8St6qSZz75OUo0tgAW4=
 github.com/brianvoe/gofakeit/v6 v6.28.0/go.mod h1:Xj58BMSnFqcn/fAQeSK+/PLtC5kSb7FJIq4JyGa8vEs=
 github.com/bufbuild/protocompile v0.14.2-0.20260121154354-91940cd2bca3 h1:7wRdWMBC4bFiS66NRJtMWRimxYik53CKtcU8KPP1EMg=
 github.com/bufbuild/protocompile v0.14.2-0.20260121154354-91940cd2bca3/go.mod h1:H51HpPHpeLddOIg/OZAuZsPmlKvP8pyXKXAkOUin9ZM=
+github.com/bufbuild/protocompile v0.14.2-0.20260130195850-5c64bed4577e h1:emH16Bf1w4C0cJ3ge4QtBAl4sIYJe23EfpWH0SpA9co=
+github.com/bufbuild/protocompile v0.14.2-0.20260130195850-5c64bed4577e/go.mod h1:cxhE8h+14t0Yxq2H9MV/UggzQ1L0gh0t2tJobITWsBE=
 github.com/bufbuild/protoplugin v0.0.0-20250218205857-750e09ce93e1 h1:V1xulAoqLqVg44rY97xOR+mQpD2N+GzhMHVwJ030WEU=
 github.com/bufbuild/protoplugin v0.0.0-20250218205857-750e09ce93e1/go.mod h1:c5D8gWRIZ2HLWO3gXYTtUfw/hbJyD8xikv2ooPxnklQ=
 github.com/cenkalti/backoff/v4 v4.3.0 h1:MyRJ/UdXutAwSAT+s3wNd7MfTIcy71VQueUuFK343L8=

private/buf/buflsp/buflsp_test.go

@@ -121,26 +121,20 @@ func setupLSPServer(
 
 	stream := jsonrpc2.NewStream(serverConn)
 
-	go func() {
-		conn, err := buflsp.Serve(
-			ctx,
-			"test",
-			wktBucket,
-			appextContainer,
-			controller,
-			wasmRuntime,
-			stream,
-			queryExecutor,
-		)
-		if err != nil {
-			t.Errorf("Failed to start server: %v", err)
-			return
-		}
-		t.Cleanup(func() {
-			require.NoError(t, conn.Close())
-		})
-		<-ctx.Done()
-	}()
+	conn, err := buflsp.Serve(
+		ctx,
+		"test",
+		wktBucket,
+		appextContainer,
+		controller,
+		wasmRuntime,
+		stream,
+		queryExecutor,
+	)
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		require.NoError(t, conn.Close())
+	})
 
 	clientStream := jsonrpc2.NewStream(clientConn)
 	clientJSONConn := jsonrpc2.NewConn(clientStream)

private/buf/buflsp/diagnostic.go

@@ -17,10 +17,8 @@
 package buflsp
 
 import (
-	"encoding/json"
-	"strings"
-
 	"github.com/bufbuild/protocompile/experimental/report"
+	"github.com/bufbuild/protocompile/experimental/report/tags"
 	"github.com/bufbuild/protocompile/experimental/source/length"
 	"go.lsp.dev/protocol"
 )
@@ -30,14 +28,6 @@ import (
 // https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#position
 const positionalEncoding = length.UTF16
 
-// diagnosticData is a structure to hold the [report.Diagnostic] notes, help, and debug
-// messages, to marshal into JSON for the [protocol.Diagnostic].Data field.
-type diagnosticData struct {
-	Notes string `json:"notes,omitempty"`
-	Help  string `json:"help,omitempty"`
-	Debug string `json:"debug,omitempty"`
-}
-
 // reportLevelToDiagnosticSeverity is a mapping of [report.Level] to [protocol.DiagnosticSeverity].
 var reportLevelToDiagnosticSeverity = map[report.Level]protocol.DiagnosticSeverity{
 	report.ICE:     protocol.DiagnosticSeverityError,
@@ -70,20 +60,15 @@ func reportDiagnosticToProtocolDiagnostic(
 			},
 		}
 	}
-	data := diagnosticData{
-		Notes: strings.Join(reportDiagnostic.Notes(), "\n"),
-		Help:  strings.Join(reportDiagnostic.Help(), "\n"),
-		Debug: strings.Join(reportDiagnostic.Debug(), "\n"),
-	}
-	bytes, err := json.Marshal(data)
-	if err != nil {
-		return protocol.Diagnostic{}, err
-	}
-	if bytes != nil {
-		// We serialize the bytes into a string before providing the structure to diagnostic.Data
-		// because diagnostic.Data is an interface{}, which is treated as a JSON "any", which
-		// will not cleanly deserialize.
-		diagnostic.Data = string(bytes)
+	switch reportDiagnostic.Tag() {
+	case tags.UnusedImport:
+		diagnostic.Tags = []protocol.DiagnosticTag{
+			protocol.DiagnosticTagUnnecessary,
+		}
+	case tags.Deprecated:
+		diagnostic.Tags = []protocol.DiagnosticTag{
+			protocol.DiagnosticTagDeprecated,
+		}
 	}
 	return diagnostic, nil
 }