zc: add the defer statement

defer expr; and defer { ... } register code that runs when the enclosing
block ends: at the end of the block, and at return, break and continue
that leave it. the tokens are kept at the defer and compiled again at each
exit (block_close, body, kw_return, kw_break, kw_continue), newest first,
before the block's variables are released, so the analyzer sees a deferred
rt.free(p) as the transfer of p where it runs. names mean what they meant
at the defer; values are read when it runs. return, break and continue
inside a deferred statement are errors, reported once. works in unchecked
code and closures (own base per function context).

4 files changed, 39 insertions, 0 deletions

diff --git a/tests/langerrors/defer_break.zc b/tests/langerrors/defer_break.zc
new file mode 100644
index 0000000..193f3f0
--- /dev/null
+++ b/tests/langerrors/defer_break.zc
@@ -0,0 +1,11 @@
+namespace;
+include rt;
+
+// expect: break can't leave a deferred statement
+fn main() {
+	while (1) {
+		defer { break; }
+		rt.put_n(1);
+	}
+	return 0;
+}
diff --git a/tests/langerrors/defer_continue.zc b/tests/langerrors/defer_continue.zc
new file mode 100644
index 0000000..079b02b
--- /dev/null
+++ b/tests/langerrors/defer_continue.zc
@@ -0,0 +1,11 @@
+namespace;
+include rt;
+
+// expect: continue can't leave a deferred statement
+fn main() {
+	for (let i = 0; i < 2; i++) {
+		defer { continue; }
+		rt.put_n(i);
+	}
+	return 0;
+}
diff --git a/tests/langerrors/defer_later_name.zc b/tests/langerrors/defer_later_name.zc
new file mode 100644
index 0000000..17f175d
--- /dev/null
+++ b/tests/langerrors/defer_later_name.zc
@@ -0,0 +1,9 @@
+namespace;
+include rt;
+
+// expect: y is used but never defined
+fn main() {
+	defer rt.put_n(y);
+	int y = 3;
+	return 0;
+}
diff --git a/tests/langerrors/defer_return.zc b/tests/langerrors/defer_return.zc
new file mode 100644
index 0000000..bceefe0
--- /dev/null
+++ b/tests/langerrors/defer_return.zc
@@ -0,0 +1,8 @@
+namespace;
+include rt;
+
+// expect: return can't be used in a deferred statement
+fn main() {
+	defer { rt.put_n(1); return 1; }
+	return 0;
+}