[Macros] Verify '-load-plugin-library' precedes '-plugin-path'

Add a test case to prevent regressions.

rdar://108285056

Author: rintaro

test/Macros/macro_mixedpluginpath.swift

@@ -0,0 +1,74 @@
+// REQUIRES: swift_swift_parser
+
+// RUN: %empty-directory(%t/src)
+// RUN: %empty-directory(%t/plugins)
+// RUN: %empty-directory(%t/plugins_local)
+
+// RUN: split-file %s %t/src
+
+
+//#-- Prepare the macro dylib plugin.
+// RUN: %host-build-swift \
+// RUN:   -swift-version 5 \
+// RUN:   -emit-library -o %t/plugins/%target-library-name(MacroDefinition) \
+// RUN:   -module-name MacroDefinition \
+// RUN:   %t/src/MacroDefinition.float.swift \
+// RUN:   -g -no-toolchain-stdlib-rpath
+
+//#-- Prepare the macro dylib plugin.
+// RUN: %host-build-swift \
+// RUN:   -swift-version 5 \
+// RUN:   -emit-library -o %t/plugins_local/%target-library-name(MacroDefinition) \
+// RUN:   -module-name MacroDefinition \
+// RUN:   %t/src/MacroDefinition.int.swift \
+// RUN:   -g -no-toolchain-stdlib-rpath
+
+//#-- Check '-load-plugin-library' precedes '-plugin-path'
+// RUN: %target-swift-frontend -typecheck -verify -swift-version 5 \
+// RUN:   -plugin-path %t/plugins \
+// RUN:   -load-plugin-library %t/plugins_local/%target-library-name(MacroDefinition) \
+// RUN:   %t/src/test.swift
+
+//#-- Check '-load-plugin-library' precedes '-plugin-path'
+// RUN: %target-swift-frontend -typecheck -verify -swift-version 5 \
+// RUN:   -load-plugin-library %t/plugins_local/%target-library-name(MacroDefinition) \
+// RUN:   -plugin-path %t/plugins \
+// RUN:   %t/src/test.swift
+
+//--- test.swift
+@freestanding(expression) macro constInt() -> Int = #externalMacro(module: "MacroDefinition", type: "ConstMacro")
+
+func foo() {
+  let _: Int = #constInt
+  // If 'MacroDefinition.float.swift' is loaded, type checking this fails because it expands to '4.2' which is a float literal.
+}
+
+//--- MacroDefinition.float.swift
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public struct ConstMacro: ExpressionMacro {
+  public static func expansion(
+    of macro: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) -> ExprSyntax {
+
+    return "4.2"
+  }
+}
+
+//--- MacroDefinition.int.swift
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public struct ConstMacro: ExpressionMacro {
+  public static func expansion(
+    of macro: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) -> ExprSyntax {
+
+    return "42"
+  }
+}