Add tests for returning by reference

Issue #918

src/test/compile-fail/ret-by-reference-from-temporary.rs

@@ -0,0 +1,9 @@
+// error-pattern:a reference binding can't be rooted in a temporary
+
+fn f(a: {x: int}) -> &int {
+    ret a.x;
+}
+
+fn main() {
+    let &_a = f({x: 4});
+}

src/test/compile-fail/ret-by-reference-local-value.rs

@@ -0,0 +1,8 @@
+// error-pattern:can not return a reference to a function-local value
+
+fn f(a: {mutable x: int}) -> &int {
+    let x = {y: 4};
+    ret x.y;
+}
+
+fn main() {}

src/test/compile-fail/ret-by-reference-mutable-field.rs

@@ -0,0 +1,7 @@
+// error-pattern:can not return a reference to a mutable field
+
+fn f(a: {mutable x: int}) -> &int {
+    ret a.x;
+}
+
+fn main() {}

src/test/compile-fail/ret-by-reference-safety-1.rs

@@ -0,0 +1,12 @@
+// error-pattern:taking the value of x will invalidate reference a
+
+fn f(a: {mutable x: int}) -> &!int {
+    ret a.x;
+}
+
+fn main() {
+    let x = {mutable x: 4};
+    let &a = f(x);
+    x;
+    a;
+}

src/test/compile-fail/ret-by-reference-safety-2.rs

@@ -0,0 +1,12 @@
+// error-pattern:overwriting x will invalidate reference a
+
+fn f(a: {x: {mutable x: int}}) -> &{mutable x: int} {
+    ret a.x;
+}
+
+fn main() {
+    let x = {x: {mutable x: 4}};
+    let &a = f(x);
+    x = {x: {mutable x: 5}};
+    a;
+}

src/test/compile-fail/ret-by-reference-specify-param.rs

@@ -0,0 +1,7 @@
+// error-pattern:must specify referenced parameter
+
+fn f(a: int, b: int) -> &int {
+    ret a;
+}
+
+fn main() {}

src/test/compile-fail/ret-by-reference-temporary.rs

@@ -0,0 +1,7 @@
+// error-pattern:can not return a reference to a temporary
+
+fn f(a: int) -> &int {
+    ret 10;
+}
+
+fn main() {}

src/test/compile-fail/ret-by-reference-wrong-param.rs

@@ -0,0 +1,7 @@
+// error-pattern:can not return a reference to the wrong parameter
+
+fn f(a: int, b: int) -> &1 int {
+    ret a;
+}
+
+fn main() {}

src/test/run-pass/ret-by-reference.rs

@@ -0,0 +1,23 @@
+tag option<T> { some(T); none; }
+
+fn get<@T>(opt: option<T>) -> &T {
+    alt opt {
+      some(x) { ret x; }
+    }
+}
+
+fn get_mut(a: {mutable x: @int}, _b: int) -> &!0 @int {
+    ret a.x;
+}
+
+fn main() {
+    let x = some(@50);
+    let &y = get(x);
+    assert *y == 50;
+    assert get(some(10)) == 10;
+
+    let y = {mutable x: @50};
+    let &box = get_mut(y, 4);
+    assert *box == 50;
+    assert *get_mut({mutable x: @70}, 5) == 70;
+}