Add -print-target-info libSwiftScan entry-points

This change adds the relevant API entry-points to `SwiftScan`.
It does not yet transition the driver's current use-sites where we shell out a `swift-frontend` process, but should make it easy to do so.

Author: artemcm

Sources/CSwiftScan/include/swiftscan_header.h

@@ -193,6 +193,10 @@ typedef struct {
   void
   (*swiftscan_scan_invocation_dispose)(swiftscan_scan_invocation_t);
 
+  //=== Target Info Functions-------- ---------------------------------------===//
+  swiftscan_string_ref_t
+  (*swiftscan_compiler_target_info_query)(swiftscan_scan_invocation_t);
+
   //=== Functionality Query Functions ---------------------------------------===//
   swiftscan_string_set_t *
   (*swiftscan_compiler_supported_arguments_query)(void);

Sources/SwiftDriver/SwiftScan/SwiftScan.swift

@@ -55,7 +55,7 @@ public enum DependencyScanningError: Error, DiagnosticData {
 }
 
 /// Wrapper for libSwiftScan, taking care of initialization, shutdown, and dispatching dependency scanning queries.
-internal final class SwiftScan {
+@_spi(Testing) public final class SwiftScan {
   /// The path to the libSwiftScan dylib.
   let path: AbsolutePath
 
@@ -246,6 +246,26 @@ internal final class SwiftScan {
       throw DependencyScanningError.argumentQueryFailed
     }
   }
+
+  @_spi(Testing) public func canQueryTargetInfo() -> Bool {
+    return api.swiftscan_compiler_target_info_query != nil &&
+           api.swiftscan_string_set_dispose != nil
+  }
+
+  @_spi(Testing) public func queryTargetInfo(invocationCommand: [String])
+  throws -> FrontendTargetInfo {
+    // Create and configure the scanner invocation
+    let invocation = api.swiftscan_scan_invocation_create()
+    defer { api.swiftscan_scan_invocation_dispose(invocation) }
+    withArrayOfCStrings(invocationCommand) { invocationStringArray in
+      api.swiftscan_scan_invocation_set_argv(invocation,
+                                             Int32(invocationCommand.count),
+                                             invocationStringArray)
+    }
+    let targetInfoString = try toSwiftString(api.swiftscan_compiler_target_info_query(invocation))
+    let targetInfoData = Data(targetInfoString.utf8)
+    return try JSONDecoder().decode(FrontendTargetInfo.self, from: targetInfoData)
+  }
 }
 
 // Used for testing purposes only
@@ -285,6 +305,10 @@ private extension swiftscan_functions_t {
     self.swiftscan_compiler_supported_features_query =
       try loadOptional("swiftscan_compiler_supported_features_query")
 
+    // Target Info query
+    self.swiftscan_compiler_target_info_query =
+      try loadOptional("swiftscan_compiler_target_info_query")
+
     // Dependency scanner serialization/deserialization features
     self.swiftscan_scanner_cache_serialize =
       try loadOptional("swiftscan_scanner_cache_serialize")

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -3840,6 +3840,22 @@ final class SwiftDriverTests: XCTestCase {
       XCTAssertTrue(job.commandLine.contains(.flag("-resource-dir")))
     }
 
+    do {
+      let targetInfoArgs = ["-print-target-info", "-target", "arm64-apple-ios12.0", "-sdk", "bar", "-resource-dir", "baz"]
+      let driver = try Driver(args: ["swift"] + targetInfoArgs)
+
+      let env = ProcessEnv.vars
+      let swiftScanLibPath = try Driver.getScanLibPath(of: driver.toolchain,
+                                                       hostTriple: driver.hostTriple,
+                                                       env: env)
+      if localFileSystem.exists(swiftScanLibPath) {
+        let libSwiftScanInstance = try SwiftScan(dylib: swiftScanLibPath)
+        if libSwiftScanInstance.canQueryTargetInfo() {
+          let _ = try libSwiftScanInstance.queryTargetInfo(invocationCommand: targetInfoArgs)
+        }
+      }
+    }
+
     do {
       struct MockExecutor: DriverExecutor {
         let resolver: ArgsResolver