Modules are pure.

test/libsolidity/syntaxTests/imports/import_access_struct.sol

@@ -0,0 +1,14 @@
+==== Source: a ====
+struct S { uint x; }
+==== Source: b ====
+import "a" as A;
+struct T { uint x; }
+contract C {
+    function f() public pure {
+        T;
+        A.S;
+    }
+}
+// ----
+// Warning: (b:90-91): Statement has no effect.
+// Warning: (b:101-104): Statement has no effect.

test/libsolidity/syntaxTests/imports/transitive.sol

@@ -0,0 +1,15 @@
+==== Source: a ====
+struct S { uint[2] mS; }
+==== Source: b ====
+import "a" as A;
+struct T { A.S[2] mT; }
+==== Source: c ====
+pragma experimental ABIEncoderV2;
+import "b" as B;
+contract C {
+    function f(B.T memory y, B.A.S memory z) public pure returns (uint, uint) {
+        z = B.A.S([uint(2), 3]);
+        y = B.T([z, z]);
+        return (y.mT[0].mS[0], z.mS[0]);
+    }
+}