Stop SpiClient soundness from regressing

...by adding a regression test with trybuild!
Adds ui tests using trybuild's test runner.

pgrx-tests/Cargo.toml

@@ -61,6 +61,7 @@ rand = "0.8.5"
 
 [dev-dependencies]
 eyre = "0.6.8"  # testing functions that return `eyre::Result`
+trybuild = "1"
 
 [dependencies.pgrx]
 path = "../pgrx"

pgrx-tests/tests/ui.rs

@@ -0,0 +1,8 @@
+use trybuild::TestCases;
+
+#[test]
+fn ui() {
+    let t = TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+}
+

pgrx-tests/tests/ui/escaping-spiclient-1209-cursor.rs

@@ -0,0 +1,27 @@
+use pgrx::prelude::*;
+use std::error::Error;
+
+#[pg_test]
+fn issue1209() -> Result<Option<String>, Box<dyn Error>> {
+    // create the cursor we actually care about
+    let mut res = Spi::connect(|c| {
+        c.open_cursor("select 'hello' from generate_series(1, 10000)", None)
+            .fetch(10000)
+            .unwrap()
+    });
+
+    // here we just perform some allocations to make sure that the previous cursor gets invalidated
+    for _ in 0..1000 {
+        Spi::connect(|c| c.open_cursor("select 1", None).fetch(1).unwrap());
+    }
+
+    // later elements are probably more likely to point to deallocated memory
+    for _ in 0..1000 {
+        res.next();
+    }
+
+    // segfault
+    Ok(res.next().unwrap().get::<String>(1)?)
+}
+
+fn main() {}

pgrx-tests/tests/ui/escaping-spiclient-1209-cursor.stderr

@@ -0,0 +1,45 @@
+error: lifetime may not live long enough
+  --> tests/ui/escaping-spiclient-1209-cursor.rs:8:9
+   |
+7  |       let mut res = Spi::connect(|c| {
+   |                                   -- return type of closure is SpiTupleTable<'2>
+   |                                   |
+   |                                   has type `SpiClient<'1>`
+8  | /         c.open_cursor("select 'hello' from generate_series(1, 10000)", None)
+9  | |             .fetch(10000)
+10 | |             .unwrap()
+   | |_____________________^ returning this value requires that `'1` must outlive `'2`
+
+error[E0515]: cannot return value referencing temporary value
+  --> tests/ui/escaping-spiclient-1209-cursor.rs:8:9
+   |
+8  |           c.open_cursor("select 'hello' from generate_series(1, 10000)", None)
+   |           ^-------------------------------------------------------------------
+   |           |
+   |  _________temporary value created here
+   | |
+9  | |             .fetch(10000)
+10 | |             .unwrap()
+   | |_____________________^ returns a value referencing data owned by the current function
+   |
+   = help: use `.collect()` to allocate the iterator
+
+error: lifetime may not live long enough
+  --> tests/ui/escaping-spiclient-1209-cursor.rs:15:26
+   |
+15 |         Spi::connect(|c| c.open_cursor("select 1", None).fetch(1).unwrap());
+   |                       -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'2`
+   |                       ||
+   |                       |return type of closure is SpiTupleTable<'2>
+   |                       has type `SpiClient<'1>`
+
+error[E0515]: cannot return value referencing temporary value
+  --> tests/ui/escaping-spiclient-1209-cursor.rs:15:26
+   |
+15 |         Spi::connect(|c| c.open_cursor("select 1", None).fetch(1).unwrap());
+   |                          -------------------------------^^^^^^^^^^^^^^^^^^
+   |                          |
+   |                          returns a value referencing data owned by the current function
+   |                          temporary value created here
+   |
+   = help: use `.collect()` to allocate the iterator

pgrx-tests/tests/ui/escaping-spiclient-1209-prep-stmt.rs

@@ -0,0 +1,13 @@
+use pgrx::prelude::*;
+use std::error::Error;
+
+#[pg_extern]
+fn issue1209_prepared_stmt(q: &str) -> Result<Option<String>, Box<dyn Error>> {
+    use pgrx::spi::Query;
+
+    let prepared = { Spi::connect(|c| c.prepare(q, None))? };
+
+    Ok(Spi::connect(|c| prepared.execute(&c, Some(1), None)?.first().get(1))?)
+}
+
+fn main() {}

pgrx-tests/tests/ui/escaping-spiclient-1209-prep-stmt.stderr

@@ -0,0 +1,8 @@
+error: lifetime may not live long enough
+ --> tests/ui/escaping-spiclient-1209-prep-stmt.rs:8:39
+  |
+8 |     let prepared = { Spi::connect(|c| c.prepare(q, None))? };
+  |                                    -- ^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'2`
+  |                                    ||
+  |                                    |return type of closure is std::result::Result<PreparedStatement<'2>, pgrx::spi::Error>
+  |                                    has type `SpiClient<'1>`