feat: generated and identity columns for mssql, sqlite, drizzle, typeorm, bun and gorm readers

- mssql: write computed columns (AS (expr) PERSISTED) and identity; read computed definition and identity
- sqlite: write GENERATED ALWAYS AS (expr) STORED; read generated columns via table_xinfo and parse the expression
- drizzle: generatedAlwaysAs / generated(Always|ByDefault)AsIdentity, read and write
- typeorm: asExpression/generatedType and identity decorators, read and write; decorator scan is now quote-aware
- bun, gorm readers: read generated and identity markers
- readmes updated

pkg/readers/sqlite/generated.go

@@ -0,0 +1,116 @@
+package sqlite
+
+import (
+	"regexp"
+	"strings"
+)
+
+var generatedAsRegex = regexp.MustCompile(`(?is)\bAS\s*\(`)
+
+// parseGeneratedExpression extracts the expression of a generated column from a CREATE
+// TABLE statement, e.g. `full TEXT GENERATED ALWAYS AS (a || b) STORED` yields `a || b`.
+// It returns "" when the column or its expression cannot be found.
+func parseGeneratedExpression(createSQL, columnName string) string {
+	open := strings.Index(createSQL, "(")
+	if open < 0 {
+		return ""
+	}
+
+	for _, def := range splitTopLevel(createSQL[open+1:]) {
+		if !strings.EqualFold(firstIdentifier(def), columnName) {
+			continue
+		}
+		loc := generatedAsRegex.FindStringIndex(def)
+		if loc == nil {
+			return ""
+		}
+		return balancedParens(def[loc[1]-1:])
+	}
+	return ""
+}
+
+// splitTopLevel splits a table body on commas that are outside parentheses and quotes,
+// stopping at the parenthesis that closes the body.
+func splitTopLevel(body string) []string {
+	var parts []string
+	depth := 0
+	var quote byte
+	start := 0
+	for i := 0; i < len(body); i++ {
+		ch := body[i]
+		if quote != 0 {
+			if ch == quote {
+				quote = 0
+			}
+			continue
+		}
+		switch ch {
+		case '\'', '"', '`':
+			quote = ch
+		case '[':
+			quote = ']'
+		case '(':
+			depth++
+		case ')':
+			if depth == 0 {
+				return append(parts, body[start:i])
+			}
+			depth--
+		case ',':
+			if depth == 0 {
+				parts = append(parts, body[start:i])
+				start = i + 1
+			}
+		}
+	}
+	return append(parts, body[start:])
+}
+
+// firstIdentifier returns the first (possibly quoted) identifier of a column definition.
+func firstIdentifier(def string) string {
+	def = strings.TrimSpace(def)
+	if def == "" {
+		return ""
+	}
+	switch def[0] {
+	case '"', '\'', '`':
+		if end := strings.IndexByte(def[1:], def[0]); end >= 0 {
+			return def[1 : 1+end]
+		}
+	case '[':
+		if end := strings.IndexByte(def, ']'); end >= 0 {
+			return def[1:end]
+		}
+	}
+	if end := strings.IndexAny(def, " \t\r\n"); end >= 0 {
+		return def[:end]
+	}
+	return def
+}
+
+// balancedParens returns the text inside the parenthesis group that starts at s[0].
+func balancedParens(s string) string {
+	depth := 0
+	var quote byte
+	for i := 0; i < len(s); i++ {
+		ch := s[i]
+		if quote != 0 {
+			if ch == quote {
+				quote = 0
+			}
+			continue
+		}
+		switch ch {
+		case '\'', '"':
+			quote = ch
+		case '(':
+			depth++
+		case ')':
+			depth--
+			if depth == 0 {
+				return strings.TrimSpace(s[1:i])
+			}
+		}
+	}
+	return ""
+}