Bail on unwrapping conditional constraints on the source side when th…

…e source conditional is already known to be spooling out of control
microsoft · Apr 1, 2021 · b81c98b · b81c98b
1 parent 363e392
commit b81c98b
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Showing 2 changed files with 15 additions and 11 deletions.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -18390,13 +18390,19 @@ namespace ts {
                             }
                         }
                     }
-                    // conditionals _can_ be related to one another via normal constraint, as, eg, `A extends B ? O : never` should be assignable to `O`
-                    // when `O` is a conditional (`never` is trivially aissgnable to `O`, as is `O`!).
-                    const defaultConstraint = getDefaultConstraintOfConditionalType(<ConditionalType>source);
-                    if (defaultConstraint) {
-                        if (result = isRelatedTo(defaultConstraint, target, reportErrors)) {
-                            resetErrorInfo(saveErrorInfo);
-                            return result;
+
+
+                    // We'll repeatedly decompose source side conditionals if they're recursive - check if we've already recured on the constraint a lot and, if so, bail
+                    // on the comparison.
+                    if (!isDeeplyNestedType(source, sourceStack, sourceDepth)) {
+                        // conditionals _can_ be related to one another via normal constraint, as, eg, `A extends B ? O : never` should be assignable to `O`
+                        // when `O` is a conditional (`never` is trivially aissgnable to `O`, as is `O`!).
+                        const defaultConstraint = getDefaultConstraintOfConditionalType(<ConditionalType>source);
+                        if (defaultConstraint) {
+                            if (result = isRelatedTo(defaultConstraint, target, reportErrors)) {
+                                resetErrorInfo(saveErrorInfo);
+                                return result;
+                            }
                         }
                     }
                 }

diff --git a/.../reference/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.errors.txt b/.../reference/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.errors.txt
@@ -8,8 +8,7 @@ tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcre
               Type 'ReturnType<T[number]>' is not assignable to type 'A'.
                 Type 'unknown' is not assignable to type 'A'.
                   Type 'ReturnType<FunctionsObj<T>[number]>' is not assignable to type 'A'.
-                    Type 'unknown' is not assignable to type 'A'.
-                      Property 'x' is missing in type '{}' but required in type 'A'.
+                    Property 'x' is missing in type '{}' but required in type 'A'.
 
 
 ==== tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.ts (1 errors) ====
@@ -37,8 +36,7 @@ tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcre
 !!! error TS2322:               Type 'ReturnType<T[number]>' is not assignable to type 'A'.
 !!! error TS2322:                 Type 'unknown' is not assignable to type 'A'.
 !!! error TS2322:                   Type 'ReturnType<FunctionsObj<T>[number]>' is not assignable to type 'A'.
-!!! error TS2322:                     Type 'unknown' is not assignable to type 'A'.
-!!! error TS2322:                       Property 'x' is missing in type '{}' but required in type 'A'.
+!!! error TS2322:                     Property 'x' is missing in type '{}' but required in type 'A'.
 !!! related TS2728 tests/cases/compiler/genericConditionalConstrainedToUnknownNotAssignableToConcreteObject.ts:1:15: 'x' is declared here.
     }