feat(ts/analyzer): Use never for unconditional throws (#412)

Author: Desdaemon

crates/stc_ts_file_analyzer/src/analyzer/stmt/return_type.rs

@@ -69,6 +69,14 @@ impl Analyzer<'_, '_> {
         debug!("visit_stmts_for_return()");
         debug_assert!(!self.is_builtin, "builtin: visit_stmts_for_return should not be called");
 
+        let mut unconditional_throw = None;
+        for stmt in stmts {
+            if let RStmt::Throw(throws) = stmt {
+                unconditional_throw = Some(throws.span);
+                break;
+            }
+        }
+
         let cannot_fallback_to_iterable_iterator = self.rule().strict_null_checks && {
             let mut v = YieldValueUsageFinder::default();
 
@@ -95,13 +103,7 @@ impl Analyzer<'_, '_> {
 
             {
                 //  Expand return types if no element references a type parameter
-                let can_expand = values.return_types.iter().all(|ty| {
-                    if should_preserve_ref(ty) {
-                        return false;
-                    }
-
-                    true
-                });
+                let can_expand = !values.return_types.iter().any(should_preserve_ref);
 
                 if can_expand {
                     values.return_types = values
@@ -149,6 +151,12 @@ impl Analyzer<'_, '_> {
                 }
             }
 
+            {
+                if let Some(span) = unconditional_throw {
+                    values.return_types.push(Type::never(span, Default::default()));
+                }
+            }
+
             debug!("visit_stmts_for_return: types.len() = {}", values.return_types.len());
 
             let mut actual = Vec::with_capacity(values.return_types.len());

crates/stc_ts_file_analyzer/tests/pass/fn/impl/1.swc-stderr

@@ -0,0 +1,38 @@
+
+  x Type
+   ,-[$DIR/tests/pass/fn/impl/1.ts:1:1]
+ 1 | undefined === function(): number {
+   : ^^^^^^^^^
+   `----
+
+Error: 
+  > undefined
+
+  x Type
+   ,-[$DIR/tests/pass/fn/impl/1.ts:2:3]
+ 2 | throw undefined
+   :       ^^^^^^^^^
+   `----
+
+Error: 
+  > undefined
+
+  x Type
+   ,-[$DIR/tests/pass/fn/impl/1.ts:1:1]
+ 1 | ,-> undefined === function(): number {
+ 2 | |     throw undefined
+ 3 | `-> }
+   `----
+
+Error: 
+  > () => number
+
+  x Type
+   ,-[$DIR/tests/pass/fn/impl/1.ts:1:1]
+ 1 | ,-> undefined === function(): number {
+ 2 | |     throw undefined
+ 3 | `-> }
+   `----
+
+Error: 
+  > boolean

crates/stc_ts_file_analyzer/tests/pass/fn/impl/1.ts

@@ -0,0 +1,3 @@
+undefined === function(): number {
+  throw undefined
+}

crates/stc_ts_type_checker/tests/conformance/functions/functionImplementationErrors.ts.stats.rust-debug

@@ -1,6 +1,6 @@
 Stats {
     required_error: 3,
     matched_error: 1,
-    extra_error: 1,
+    extra_error: 0,
     panic: 0,
 }

crates/stc_ts_type_checker/tests/conformance/functions/functionImplementations.ts.stats.rust-debug

@@ -1,6 +1,6 @@
 Stats {
     required_error: 1,
     matched_error: 0,
-    extra_error: 4,
+    extra_error: 3,
     panic: 0,
 }

crates/stc_ts_type_checker/tests/conformance/types/typeRelationships/typeInference/keyofInferenceLowerPriorityThanReturn.ts.stats.rust-debug

@@ -1,6 +1,6 @@
 Stats {
     required_error: 0,
     matched_error: 0,
-    extra_error: 3,
+    extra_error: 2,
     panic: 0,
 }