feat(es/parser): Support extends clause to infer type (#4326)

crates/swc_ecma_parser/src/lib.rs

@@ -387,6 +387,8 @@ pub struct Context {
     allow_direct_super: bool,
 
     ignore_else_clause: bool,
+
+    disallow_conditional_types: bool,
 }
 
 #[cfg(test)]

crates/swc_ecma_parser/src/parser/typescript.rs

@@ -898,29 +898,43 @@ impl<I: Tokens> Parser<I> {
 
         let start = cur_pos!(self);
 
-        let ty = self.parse_ts_non_conditional_type()?;
+        self.with_ctx(Context {
-        if self.input.had_line_break_before_cur() || !eat!(self, "extends") {
+            disallow_conditional_types: false,
-            return Ok(ty);
+            ..self.ctx()
-        }
+        })
+        .parse_with(|p| {
+            let ty = p.parse_ts_non_conditional_type()?;
+            if p.input.had_line_break_before_cur() || !eat!(p, "extends") {
+                return Ok(ty);
+            }
 
-        let check_type = ty;
+            let check_type = ty;
-        let extends_type = self.parse_ts_non_conditional_type()?;
+            let extends_type = p.parse_ts_non_conditional_type_within_ctx()?;
 
-        expect!(self, '?');
+            expect!(p, '?');
 
-        let true_type = self.parse_ts_type()?;
+            let true_type = p.parse_ts_type()?;
 
-        expect!(self, ':');
+            expect!(p, ':');
 
-        let false_type = self.parse_ts_type()?;
+            let false_type = p.parse_ts_type()?;
 
-        Ok(Box::new(TsType::TsConditionalType(TsConditionalType {
+            Ok(Box::new(TsType::TsConditionalType(TsConditionalType {
-            span: span!(self, start),
+                span: span!(p, start),
-            check_type,
+                check_type,
-            extends_type,
+                extends_type,
-            true_type,
+                true_type,
-            false_type,
+                false_type,
-        })))
+            })))
+        })
+    }
+
+    fn parse_ts_non_conditional_type_within_ctx(&mut self) -> PResult<Box<TsType>> {
+        self.with_ctx(Context {
+            disallow_conditional_types: true,
+            ..self.ctx()
+        })
+        .parse_ts_non_conditional_type()
     }
 
     /// `tsParseNonConditionalType`
@@ -2197,12 +2211,21 @@ impl<I: Tokens> Parser<I> {
         let start = cur_pos!(self);
         expect!(self, "infer");
         let type_param_name = self.parse_ident_name()?;
+        let constraint = self.try_parse_ts(|p| {
+            expect!(p, "extends");
+            let constraint = p.parse_ts_non_conditional_type();
+            if p.ctx().disallow_conditional_types || !is!(p, '?') {
+                constraint.map(Some)
+            } else {
+                Ok(None)
+            }
+        });
         let type_param = TsTypeParam {
             span: type_param_name.span(),
             name: type_param_name,
             is_in: false,
             is_out: false,
-            constraint: None,
+            constraint,
             default: None,
         };
         Ok(TsInferType {

crates/swc_ecma_parser/tests/typescript/types/conditional-infer-extends/basic/input.ts

@@ -0,0 +1,29 @@
+type X1<T extends any[]> =
+    T extends [infer U extends string] ? ["string", U] :
+    T extends [infer U extends number] ? ["number", U] :
+    never;
+
+type X2<T extends (...args: any[]) => void> =
+    T extends (a: infer U extends string) => void ? ["string", U] :
+    T extends (a: infer U extends number) => void ? ["number", U] :
+    never;
+
+type X3<T extends (...args: any[]) => any> =
+    T extends (...args: any[]) => (infer U extends string) ? ["string", U] :
+    T extends (...args: any[]) => (infer U extends number) ? ["number", U] :
+    never;
+
+type X4<T extends new (...args: any[]) => any> =
+    T extends new (...args: any[]) => (infer U extends { a: string }) ? ["string", U] :
+    T extends new (...args: any[]) => (infer U extends { a: number }) ? ["number", U] :
+    never;
+
+type X5<T> =
+    T extends Promise<infer U extends string> ? ["string", U] :
+    T extends Promise<infer U extends number> ? ["number", U] :
+    never;
+
+type X6<T> =
+    T extends { a: infer U extends string } ? ["string", U] :
+    T extends { a: infer U extends number } ? ["number", U] :
+    never;

crates/swc_ecma_parser/tests/typescript/types/conditional-infer-extends/distinguishing/input.ts

@@ -0,0 +1,9 @@
+type X10<T> = T extends (infer U extends number ? 1 : 0) ? 1 : 0; // ok, parsed as conditional
+type X11<T> = T extends ((infer U) extends number ? 1 : 0) ? 1 : 0; // ok, parsed as conditional
+type X12<T> = T extends (infer U extends number) ? 1 : 0; // ok, parsed as `infer..extends` (no trailing `?`)
+type X13<T> = T extends infer U extends number ? 1 : 0; // ok, parsed as `infer..extends` (conditional types not allowed in 'extends type')
+type X14<T> = T extends keyof infer U extends number ? 1 : 0; // ok, parsed as `infer..extends` (precedence wouldn't have parsed the `?` as part of a type operator)
+type X15<T> = T extends { [P in infer U extends keyof T ? 1 : 0]: 1; } ? 1 : 0; // ok, parsed as conditional
+type X16<T> = T extends { [P in infer U extends keyof T]: 1; } ? 1 : 0; // ok, parsed as `infer..extends` (no trailing `?`)
+type X17<T> = T extends { [P in keyof T as infer U extends P ? 1 : 0]: 1; } ? 1 : 0; // ok, parsed as conditional
+type X18<T> = T extends { [P in keyof T as infer U extends P]: 1; } ? 1 : 0; // ok, parsed as `infer..extends` (no trailing `?`)