sqlite: quote identifiers that would not survive a reparse

fmt dropped double quotes from identifiers: the sqlite dialect's
QuoteIdent returned every name bare, and the round-trip verification
could not see the loss because it compares case-insensitively while the
parser folds unquoted identifiers to lower case — so "EmailAddress"
reprinted as EmailAddress, which sqlc's catalog then failed to resolve.

Quote any identifier that is not a plain lower-case name, or that
collides with a keyword (meyer's table, case-insensitive), escaping
embedded quotes. The fmt endtoend case now pins quoted mixed-case and
keyword identifiers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018MTvpHqNMadH12pTtsgUq2

Author: claude

internal/endtoend/testdata/fmt/sqlite/query.sql

@@ -18,3 +18,7 @@ SELECT /* inline note */ id, name FROM authors ORDER BY name;
 -- name: ListAuthors :many
 SELECT id, name, bio FROM authors
 ORDER BY name;
+
+-- name: GetEvent :one
+SELECT "EventName", "order"
+FROM "Events" WHERE id = ? LIMIT 1;

internal/endtoend/testdata/fmt/sqlite/schema.sql

@@ -3,3 +3,9 @@ CREATE TABLE authors (
   name text NOT NULL,
   bio text
 );
+
+CREATE TABLE "Events" (
+  id integer PRIMARY KEY,
+  "EventName" text NOT NULL,
+  "order" integer NOT NULL
+);

internal/endtoend/testdata/fmt/sqlite/stdout.txt

@@ -22,11 +22,19 @@
  FROM authors
  -- soft-deleted rows are filtered
  WHERE bio IS NOT NULL
-@@ -16,5 +19,6 @@
+@@ -16,7 +19,8 @@
  SELECT /* inline note */ id, name FROM authors ORDER BY name;
 
  -- name: ListAuthors :many
 +SELECT id, name, bio
 +FROM authors
 -SELECT id, name, bio FROM authors
  ORDER BY name;
+ 
+ -- name: GetEvent :one
+@@ -23,2 +27,4 @@
+ SELECT "EventName", "order"
++FROM "Events"
++WHERE id = ?
++LIMIT 1;
+-FROM "Events" WHERE id = ? LIMIT 1;

internal/engine/sqlite/format.go

@@ -1,13 +1,35 @@
 package sqlite
 
-// QuoteIdent returns a quoted identifier if it needs quoting.
-// SQLite uses double quotes for quoting identifiers (SQL standard),
-// though backticks are also supported for MySQL compatibility.
+import "strings"
+
+// QuoteIdent quotes an identifier when printing it bare would change what it
+// names: the parser folds unquoted identifiers to lower case, so any name
+// that is not already a plain lower-case identifier — or that collides with
+// a keyword — only survives a parse round-trip inside double quotes.
 func (p *Parser) QuoteIdent(s string) string {
-	// For now, don't quote - return as-is
+	if s == "" || p.IsReservedKeyword(s) || !plainIdent(s) {
+		return `"` + strings.ReplaceAll(s, `"`, `""`) + `"`
+	}
 	return s
 }
 
+// plainIdent reports whether s parses back as itself unquoted: ASCII
+// lower-case letters, digits and underscores, not starting with a digit.
+func plainIdent(s string) bool {
+	for i, r := range s {
+		switch {
+		case r >= 'a' && r <= 'z', r == '_':
+		case r >= '0' && r <= '9':
+			if i == 0 {
+				return false
+			}
+		default:
+			return false
+		}
+	}
+	return true
+}
+
 // TypeName returns the SQL type name for the given namespace and name.
 func (p *Parser) TypeName(ns, name string) string {
 	if ns != "" {