feat(lsp): add textDocument/rangeFormatting support

Advertise DocumentRangeFormattingProvider in server capabilities and
implement rangeFormat: formats the complete document, then returns an
edit covering only the minimal changed-line region that overlaps the
client's selection. Also includes gofmt alignment fixes across lint
and format packages.

pkg/format/body.go

@@ -215,13 +215,13 @@ func formatBodyStatements(text string, st config.Style) string {
 	rawLines := strings.Split(normalised, "\n")
 
 	var (
-		result       strings.Builder
-		stmt         []bline
-		parenDepth   int
-		blockDepth   int // 0=col-0 (BEGIN/END/EXCEPTION), 1=body, 2=nested…
-		inException  bool
+		result        strings.Builder
+		stmt          []bline
+		parenDepth    int
+		blockDepth    int // 0=col-0 (BEGIN/END/EXCEPTION), 1=body, 2=nested…
+		inException   bool
 		pendingBlanks int
-		depthInc     bool // increment blockDepth after next flush
+		depthInc      bool // increment blockDepth after next flush
 	)
 
 	flush := func() {

pkg/lint/rules_correctness.go

@@ -14,7 +14,7 @@ import (
 // break callers silently. Enumerate the columns you need explicitly.
 type ruleCOR001 struct{}
 
-func (ruleCOR001) ID() string                    { return "COR001" }
+func (ruleCOR001) ID() string                     { return "COR001" }
 func (ruleCOR001) Severity() diagnostics.Severity { return diagnostics.SeverityHint }
 
 func (ruleCOR001) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -71,7 +71,7 @@ func checkSelectStmt(s *pg_query.SelectStmt, src string, out *[]diagnostics.Diag
 // An UPDATE with no WHERE clause modifies every row in the table.
 type ruleCOR002 struct{}
 
-func (ruleCOR002) ID() string                    { return "COR002" }
+func (ruleCOR002) ID() string                     { return "COR002" }
 func (ruleCOR002) Severity() diagnostics.Severity { return diagnostics.SeverityWarning }
 
 func (ruleCOR002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -101,7 +101,7 @@ func (ruleCOR002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Dia
 // Use TRUNCATE if you intend a full wipe; it is faster and explicit.
 type ruleCOR003 struct{}
 
-func (ruleCOR003) ID() string                    { return "COR003" }
+func (ruleCOR003) ID() string                     { return "COR003" }
 func (ruleCOR003) Severity() diagnostics.Severity { return diagnostics.SeverityWarning }
 
 func (ruleCOR003) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {

pkg/lint/rules_migration.go

@@ -16,7 +16,7 @@ import (
 // CREATE INDEX CONCURRENTLY instead.
 type ruleMIG001 struct{}
 
-func (ruleMIG001) ID() string                    { return "MIG001" }
+func (ruleMIG001) ID() string                     { return "MIG001" }
 func (ruleMIG001) Severity() diagnostics.Severity { return diagnostics.SeverityWarning }
 
 func (ruleMIG001) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -52,7 +52,7 @@ func (ruleMIG001) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Dia
 // supplied. Use a nullable column first, backfill, then add the constraint.
 type ruleMIG002 struct{}
 
-func (ruleMIG002) ID() string                    { return "MIG002" }
+func (ruleMIG002) ID() string                     { return "MIG002" }
 func (ruleMIG002) Severity() diagnostics.Severity { return diagnostics.SeverityWarning }
 
 func (ruleMIG002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -97,7 +97,7 @@ func (ruleMIG002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Dia
 // VALIDATE CONSTRAINT to spread the lock window.
 type ruleMIG003 struct{}
 
-func (ruleMIG003) ID() string                    { return "MIG003" }
+func (ruleMIG003) ID() string                     { return "MIG003" }
 func (ruleMIG003) Severity() diagnostics.Severity { return diagnostics.SeverityWarning }
 
 func (ruleMIG003) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {

pkg/lint/rules_naming.go

@@ -22,7 +22,7 @@ func isSnakeCase(s string) bool {
 // NAM001 — table names must be snake_case.
 type ruleNAM001 struct{}
 
-func (ruleNAM001) ID() string                    { return "NAM001" }
+func (ruleNAM001) ID() string                     { return "NAM001" }
 func (ruleNAM001) Severity() diagnostics.Severity { return diagnostics.SeverityHint }
 
 func (ruleNAM001) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -51,7 +51,7 @@ func (ruleNAM001) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Dia
 // NAM002 — column names in CREATE TABLE must be snake_case.
 type ruleNAM002 struct{}
 
-func (ruleNAM002) ID() string                    { return "NAM002" }
+func (ruleNAM002) ID() string                     { return "NAM002" }
 func (ruleNAM002) Severity() diagnostics.Severity { return diagnostics.SeverityHint }
 
 func (ruleNAM002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {
@@ -86,7 +86,7 @@ func (ruleNAM002) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Dia
 // NAM003 — function/procedure names must be snake_case.
 type ruleNAM003 struct{}
 
-func (ruleNAM003) ID() string                    { return "NAM003" }
+func (ruleNAM003) ID() string                     { return "NAM003" }
 func (ruleNAM003) Severity() diagnostics.Severity { return diagnostics.SeverityHint }
 
 func (ruleNAM003) Check(stmts []*pg_query.RawStmt, src string) []diagnostics.Diagnostic {

pkg/lsp/server.go

@@ -38,8 +38,8 @@ func Serve(ctx context.Context, r io.Reader, w io.Writer, startDir string) error
 }
 
 type server struct {
-	docs  map[string]string                    // URI → current text
-	fixes map[string][]diagnostics.Diagnostic  // URI → diagnostics that have fixes
+	docs  map[string]string                   // URI → current text
+	fixes map[string][]diagnostics.Diagnostic // URI → diagnostics that have fixes
 	cfg   config.Style
 	w     io.Writer
 }
@@ -76,9 +76,10 @@ func (s *server) handle(raw []byte) bool {
 	case "initialize":
 		s.reply(req.ID, initResult{
 			Capabilities: serverCaps{
-				TextDocumentSync:           1, // full sync
-				DocumentFormattingProvider: true,
-				CodeActionProvider:         true,
+				TextDocumentSync:                1, // full sync
+				DocumentFormattingProvider:      true,
+				DocumentRangeFormattingProvider: true,
+				CodeActionProvider:              true,
 			},
 		})
 	case "initialized": // no-op notification
@@ -124,6 +125,15 @@ func (s *server) handle(raw []byte) bool {
 			return false
 		}
 		s.reply(req.ID, []textEdit{fullReplace(text, formatted)})
+	case "textDocument/rangeFormatting":
+		var p rangeFormattingParams
+		json.Unmarshal(req.Params, &p)
+		text, ok := s.docs[p.TextDocument.URI]
+		if !ok {
+			s.reply(req.ID, []textEdit{})
+			return false
+		}
+		s.reply(req.ID, s.rangeFormat(text, p.Range))
 	case "textDocument/codeAction":
 		var p codeActionParams
 		json.Unmarshal(req.Params, &p)
@@ -205,6 +215,61 @@ func (s *server) handleCodeAction(id json.RawMessage, p codeActionParams) {
 	s.reply(id, actions)
 }
 
+// rangeFormat formats the region of text that overlaps the given LSP range.
+// It formats the complete document, then returns an edit covering only the
+// minimal set of changed lines that intersects the selection. Returns nil when
+// the document is already formatted or no change falls within the selection.
+func (s *server) rangeFormat(text string, r lspRange) []textEdit {
+	formatted := format.File(parser.Parse(text), s.cfg)
+	if formatted == text {
+		return nil
+	}
+
+	// Split both versions into lines, keeping the trailing newline attached to
+	// each element so that joining them reconstructs the original string.
+	origLines := strings.SplitAfter(text, "\n")
+	fmtLines := strings.SplitAfter(formatted, "\n")
+
+	// Longest common prefix of unchanged lines.
+	pfx := 0
+	for pfx < len(origLines) && pfx < len(fmtLines) && origLines[pfx] == fmtLines[pfx] {
+		pfx++
+	}
+	// Longest common suffix (must not overlap the prefix).
+	sfx := 0
+	for sfx < len(origLines)-pfx && sfx < len(fmtLines)-pfx &&
+		origLines[len(origLines)-1-sfx] == fmtLines[len(fmtLines)-1-sfx] {
+		sfx++
+	}
+
+	// The changed region in the original spans lines [pfx, changedEnd).
+	changedStart := pfx
+	changedEnd := len(origLines) - sfx
+
+	// Only return an edit when the changed region overlaps the selection.
+	selStart := int(r.Start.Line)
+	selEnd := int(r.End.Line)
+	if changedEnd <= selStart || changedStart > selEnd {
+		return nil
+	}
+
+	// Compute byte offsets for the changed region boundary.
+	startByte := 0
+	for i := 0; i < changedStart; i++ {
+		startByte += len(origLines[i])
+	}
+	endByte := startByte
+	for i := changedStart; i < changedEnd; i++ {
+		endByte += len(origLines[i])
+	}
+
+	newText := strings.Join(fmtLines[pfx:len(fmtLines)-sfx], "")
+	return []textEdit{{
+		Range:   lspRange{Start: offsetToPosition(text, startByte), End: offsetToPosition(text, endByte)},
+		NewText: newText,
+	}}
+}
+
 // offsetToPosition converts a byte offset in text to an LSP position.
 func offsetToPosition(text string, byteOff int) position {
 	if byteOff > len(text) {
@@ -360,9 +425,10 @@ type initResult struct {
 }
 
 type serverCaps struct {
-	TextDocumentSync           int  `json:"textDocumentSync"`
-	DocumentFormattingProvider bool `json:"documentFormattingProvider"`
-	CodeActionProvider         bool `json:"codeActionProvider"`
+	TextDocumentSync                int  `json:"textDocumentSync"`
+	DocumentFormattingProvider      bool `json:"documentFormattingProvider"`
+	DocumentRangeFormattingProvider bool `json:"documentRangeFormattingProvider"`
+	CodeActionProvider              bool `json:"codeActionProvider"`
 }
 
 type textDocItem struct {
@@ -397,6 +463,15 @@ type formattingParams struct {
 	} `json:"options"`
 }
 
+type rangeFormattingParams struct {
+	TextDocument textDocID `json:"textDocument"`
+	Range        lspRange  `json:"range"`
+	Options      struct {
+		TabSize      int  `json:"tabSize"`
+		InsertSpaces bool `json:"insertSpaces"`
+	} `json:"options"`
+}
+
 type lspDiagnostic struct {
 	Range    lspRange `json:"range"`
 	Severity int      `json:"severity"`

pkg/lsp/server_test.go

@@ -156,6 +156,76 @@ func TestFormatting(t *testing.T) {
 	}
 }
 
+func TestRangeFormatting(t *testing.T) {
+	// Two statements: first is unformatted, second is already formatted.
+	// Range request covers only the first statement (line 0).
+	sql := "select a, b from t where x = 1;\nSELECT z\nFROM s;\n"
+	uri := "file:///range.sql"
+
+	var input []byte
+	input = append(input, frame(1, "initialize", map[string]interface{}{})...)
+	input = append(input, notifFrame("initialized", nil)...)
+	input = append(input, notifFrame("textDocument/didOpen", map[string]interface{}{
+		"textDocument": map[string]interface{}{
+			"uri": uri, "languageId": "sql", "version": 1, "text": sql,
+		},
+	})...)
+	input = append(input, frame(2, "textDocument/rangeFormatting", map[string]interface{}{
+		"textDocument": map[string]interface{}{"uri": uri},
+		"range": map[string]interface{}{
+			"start": map[string]interface{}{"line": 0, "character": 0},
+			"end":   map[string]interface{}{"line": 0, "character": 31},
+		},
+		"options": map[string]interface{}{"tabSize": 2, "insertSpaces": true},
+	})...)
+	input = append(input, frame(3, "shutdown", nil)...)
+	input = append(input, notifFrame("exit", nil)...)
+
+	out := runServer(t, input)
+
+	var resp map[string]interface{}
+	for i := 0; i < 10; i++ {
+		r := readResp(t, out)
+		if r == nil {
+			break
+		}
+		if id, ok := r["id"]; ok && id.(float64) == 2 {
+			resp = r
+			break
+		}
+	}
+	if resp == nil {
+		t.Fatal("no response for rangeFormatting request")
+	}
+	result, ok := resp["result"].([]interface{})
+	if !ok || len(result) == 0 {
+		t.Fatalf("expected non-empty edit array, got %v", resp["result"])
+	}
+	edit := result[0].(map[string]interface{})
+	newText, _ := edit["newText"].(string)
+	if !strings.Contains(newText, "SELECT") {
+		t.Errorf("expected formatted SELECT in edit, got: %q", newText)
+	}
+	if strings.Contains(newText, "SELECT z") {
+		t.Errorf("range formatting edited second statement unexpectedly; got: %q", newText)
+	}
+}
+
+func TestInitialize_AdvertisesRangeFormatting(t *testing.T) {
+	input := append(frame(1, "initialize", map[string]interface{}{}),
+		notifFrame("initialized", map[string]interface{}{})...)
+	input = append(input, frame(2, "shutdown", nil)...)
+	input = append(input, notifFrame("exit", nil)...)
+
+	out := runServer(t, input)
+
+	resp := readResp(t, out)
+	caps := resp["result"].(map[string]interface{})["capabilities"].(map[string]interface{})
+	if caps["documentRangeFormattingProvider"] != true {
+		t.Error("expected documentRangeFormattingProvider=true")
+	}
+}
+
 func TestDidClose_ClearsDiagnostics(t *testing.T) {
 	uri := "file:///test.sql"
 	// SQL with a lint violation (SELECT * triggers COR001)