Interpreter: Apply shell expansion in ldflags (#12094)

spec/compiler/data/interpreter/sum.c

@@ -25,3 +25,7 @@ long sum_int(int count, ...) {
 
   return total;
 }
+
+int simple_sum_int(int a, int b) {
+  return a + b;
+}

spec/compiler/interpreter/lib_spec.cr

@@ -54,4 +54,26 @@ describe Crystal::Repl::Interpreter do
       FileUtils.rm_rf(SPEC_CRYSTAL_LOADER_LIB_PATH)
     end
   end
+
+  context "command expansion" do
+    before_all do
+      FileUtils.mkdir_p(SPEC_CRYSTAL_LOADER_LIB_PATH)
+      build_c_dynlib(compiler_datapath("interpreter", "sum.c"))
+    end
+
+    it "expands ldflags" do
+      interpret(<<-CR).should eq 4
+        @[Link(ldflags: "-L#{SPEC_CRYSTAL_LOADER_LIB_PATH} -l`echo sum`")]
+        lib LibSum
+          fun simple_sum_int(a : Int32, b : Int32) : Int32
+        end
+
+        LibSum.simple_sum_int(2, 2)
+        CR
+    end
+
+    after_all do
+      FileUtils.rm_rf(SPEC_CRYSTAL_LOADER_LIB_PATH)
+    end
+  end
 end

src/compiler/crystal/interpreter/context.cr

@@ -357,7 +357,11 @@ class Crystal::Repl::Context
   end
 
   getter(loader : Loader) {
-    args = Process.parse_arguments(program.lib_flags)
+    lib_flags = program.lib_flags
+    # Execute and expand `subcommands`.
+    lib_flags = lib_flags.gsub(/`(.*?)`/) { `#{$1}` }
+
+    args = Process.parse_arguments(lib_flags)
     # FIXME: Part 1: This is a workaround for initial integration of the interpreter:
     # The loader can't handle the static libgc.a usually shipped with crystal and loading as a shared library conflicts
     # with the compiler's own GC.