Implement throw & catch statements (#6916)

* Implement throw statement

It already existed in the IR, so only parsing, checking and lowering was
missing.

* Initial catch implementation

Likely very broken.

* Error out when catch() isn't last in scope

* Prevent accessing variables from scope preceding catch

As those may actually not be available at that point.

* Add IError and use it in Result type lowering

* Add diagnostic tests

* Allow caught throws in non-throw functions

* Fix catch propagating between functions & SPIR-V merge issue

* Add test for non-trivial error types

* Fix MSVC build

* Fix invalid value type from Result lowering

* Also lower error handling in templates

* Lower result types only after specialization

* Attempt to disambiguate error enums by witness table

* Revert matching by witness, types should be distinct too

* Don't assert valueField when getting Result's error value

It may not exist if the function returns void, but getting the error
value is still legitimate.

* Update tests for new error numbers & get rid of expected.txt

* Change catch lowering to resemble breaking a loop

... To make SPIR-V happy.

* Fix dead catch blocks and invalid cached dominator tree

* More SPIR-V adjustment

* Lower catch as two nested loops

* Add defer interaction test and revert broken defer changes

* Fix enum type when throwing literals

* Cleanup and bikeshedding

* Document error handling mechanism

* Fix table of contents

* Use boolean tag in Result<T, E>

* Use anyValue storage for Result<T,E>

* Remove IError

* Fix formatting

* Eradicate success values from docs and tests

* Use parseModernParamDecl for catch parameter

* Implement do-catch syntax

* Implement catch-all

* Fix formatting

* Fix marshalling native calls that throw

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/language-feature/error-handling/throw-without-throws.slang b/tests/language-feature/error-handling/throw-without-throws.slang
new file mode 100644
index 000000000..e37198b82
--- /dev/null
+++ b/tests/language-feature/error-handling/throw-without-throws.slang
@@ -0,0 +1,19 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK):
+enum MyError
+{
+    Fail
+}
+
+int g() throws MyError
+{
+    throw MyError.Fail;
+}
+
+void f()
+{
+    let n = try g();
+    throw MyError.Fail;
+}
+
+// CHECK: error 30093
+// CHECK: error 30115