From 57c3f938221c427b78da7087f8a832ba4a271a7c Mon Sep 17 00:00:00 2001
From: Julius Ikkala <julius.ikkala@gmail.com>
Date: Fri, 23 May 2025 22:27:37 +0300
Subject: 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>
---
 source/slang/slang-check-expr.cpp | 69 +++++++++++++++++++++++++--------------
 1 file changed, 44 insertions(+), 25 deletions(-)

(limited to 'source/slang/slang-check-expr.cpp')

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index db507c060..75b1b7024 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -3951,45 +3951,64 @@ Expr* SemanticsExprVisitor::visitTryExpr(TryExpr* expr)
         return expr;
 
     auto parentFunc = this->m_parentFunc;
-    // TODO: check if the try clause is caught.
-    // For now we assume all `try`s are not caught (because we don't have catch yet).
-    if (!parentFunc)
+    auto base = as<InvokeExpr>(expr->base);
+    if (!base)
     {
-        getSink()->diagnose(expr, Diagnostics::uncaughtTryCallInNonThrowFunc);
+        getSink()->diagnose(expr, Diagnostics::tryClauseMustApplyToInvokeExpr);
         return expr;
     }
-    if (parentFunc->errorType->equals(m_astBuilder->getBottomType()))
+
+    auto callee = as<DeclRefExpr>(base->functionExpr);
+    if (!callee)
     {
-        getSink()->diagnose(expr, Diagnostics::uncaughtTryCallInNonThrowFunc);
+        getSink()->diagnose(expr, Diagnostics::calleeOfTryCallMustBeFunc);
         return expr;
     }
-    if (!as<InvokeExpr>(expr->base))
+
+    auto funcCallee = as<FuncDecl>(callee->declRef.getDecl());
+    Stmt* catchStmt = nullptr;
+    if (funcCallee)
     {
-        getSink()->diagnose(expr, Diagnostics::tryClauseMustApplyToInvokeExpr);
+        if (funcCallee->errorType->equals(m_astBuilder->getBottomType()))
+        {
+            getSink()->diagnose(expr, Diagnostics::tryInvokeCalleeShouldThrow, callee->declRef);
+            return expr;
+        }
+        catchStmt = findMatchingCatchStmt(funcCallee->errorType);
+    }
+
+    if (FindOuterStmt<DeferStmt>(catchStmt))
+    {
+        // 'try' may jump outside a defer statement, which isn't allowed for
+        // now.
+        getSink()->diagnose(expr, Diagnostics::uncaughtTryInsideDefer);
         return expr;
     }
-    auto base = as<InvokeExpr>(expr->base);
-    if (auto callee = as<DeclRefExpr>(base->functionExpr))
+
+    if (!catchStmt)
     {
-        if (auto funcCallee = as<FuncDecl>(callee->declRef.getDecl()))
+        // Uncaught try.
+        if (!parentFunc)
         {
-            if (funcCallee->errorType->equals(m_astBuilder->getBottomType()))
-            {
-                getSink()->diagnose(expr, Diagnostics::tryInvokeCalleeShouldThrow, callee->declRef);
-            }
-            if (!parentFunc->errorType->equals(funcCallee->errorType))
-            {
-                getSink()->diagnose(
-                    expr,
-                    Diagnostics::errorTypeOfCalleeIncompatibleWithCaller,
-                    callee->declRef,
-                    funcCallee->errorType,
-                    parentFunc->errorType);
-            }
+            getSink()->diagnose(expr, Diagnostics::uncaughtTryCallInNonThrowFunc);
+            return expr;
+        }
+        if (parentFunc->errorType->equals(m_astBuilder->getBottomType()))
+        {
+            getSink()->diagnose(expr, Diagnostics::uncaughtTryCallInNonThrowFunc);
+            return expr;
+        }
+        if (funcCallee && !parentFunc->errorType->equals(funcCallee->errorType))
+        {
+            getSink()->diagnose(
+                expr,
+                Diagnostics::errorTypeOfCalleeIncompatibleWithCaller,
+                callee->declRef,
+                funcCallee->errorType,
+                parentFunc->errorType);
             return expr;
         }
     }
-    getSink()->diagnose(expr, Diagnostics::calleeOfTryCallMustBeFunc);
     return expr;
 }
 
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