[NFC] BridgeJS: Move CodeFragmentPrintetr to BridgeJSCore

So that we can use it for Swift code generation

Author: kateinoigakukun

Plugins/BridgeJS/Sources/BridgeJSLink/CodeFragmentPrinter.swift

@@ -1,6 +1,9 @@
 #if canImport(BridgeJSSkeleton)
 import BridgeJSSkeleton
 #endif
+#if canImport(BridgeJSUtilities)
+import BridgeJSUtilities
+#endif
 
 /// A scope for variables for JS glue code
 final class JSGlueVariableScope {

Plugins/BridgeJS/Sources/BridgeJSLink/JSGlueGen.swift

@@ -0,0 +1,37 @@
+#if canImport(BridgeJSUtilities)
+import BridgeJSUtilities
+#endif
+
+/// Registry for JS helper intrinsics used during code generation.
+final class JSIntrinsicRegistry {
+    private var entries: [String: [String]] = [:]
+
+    var isEmpty: Bool {
+        entries.isEmpty
+    }
+
+    func register(name: String, build: (CodeFragmentPrinter) throws -> Void) rethrows {
+        guard entries[name] == nil else { return }
+        let printer = CodeFragmentPrinter()
+        try build(printer)
+        entries[name] = printer.lines
+    }
+
+    func reset() {
+        entries.removeAll()
+    }
+
+    func emitLines() -> [String] {
+        var emitted: [String] = []
+        for key in entries.keys.sorted() {
+            if let lines = entries[key] {
+                emitted.append(contentsOf: lines)
+                emitted.append("")
+            }
+        }
+        if emitted.last == "" {
+            emitted.removeLast()
+        }
+        return emitted
+    }
+}

Plugins/BridgeJS/Sources/BridgeJSLink/JSIntrinsicRegistry.swift

@@ -27,3 +27,50 @@ public enum BridgeJSGeneratedFile {
         """
     }
 }
+
+/// A printer for code fragments.
+public final class CodeFragmentPrinter {
+    public private(set) var lines: [String] = []
+    private var indentLevel: Int = 0
+
+    public init(header: String = "") {
+        self.lines.append(contentsOf: header.split(separator: "\n").map { String($0) })
+    }
+
+    public func nextLine() {
+        lines.append("")
+    }
+
+    public func write<S: StringProtocol>(_ line: S) {
+        if line.isEmpty {
+            // Empty lines should not have trailing spaces
+            lines.append("")
+            return
+        }
+        lines.append(String(repeating: " ", count: indentLevel * 4) + String(line))
+    }
+
+    public func write(lines: [String]) {
+        for line in lines {
+            write(line)
+        }
+    }
+
+    public func write(contentsOf printer: CodeFragmentPrinter) {
+        self.write(lines: printer.lines)
+    }
+
+    public func indent() {
+        indentLevel += 1
+    }
+
+    public func unindent() {
+        indentLevel -= 1
+    }
+
+    public func indent(_ body: () throws -> Void) rethrows {
+        indentLevel += 1
+        try body()
+        indentLevel -= 1
+    }
+}