Elaborate readonly array/tuple relation errors. Fixes microsoft#35060

src/compiler/checker.ts

@@ -14537,6 +14537,13 @@ namespace ts {
                 if (isTupleLikeType(source)) {
                     const sourceTuple: TupleType | undefined  = (source as TupleTypeReference).target;
                     if (sourceTuple && sourceTuple.readonly && isArrayOrTupleLikeType(target) &&
+                        (isReadonlyArrayType(target) || isTupleType(target) && target.target.readonly)) {
+                        if (reportErrors) {
+                            reportError(Diagnostics.The_type_0_is_readonly_and_is_incompatible_with_type_1, typeToString(source), typeToString(target));
+                        }
+                        return false;
+                    }
+                    else if (sourceTuple && sourceTuple.readonly && isArrayOrTupleLikeType(target) &&
                         (!isReadonlyArrayType(target) || isTupleType(target) && !target.target.readonly)) {
                         if (reportErrors) {
                             reportError(Diagnostics.The_type_0_is_readonly_and_cannot_be_assigned_to_the_mutable_type_1, typeToString(source), typeToString(target));
@@ -14554,6 +14561,12 @@ namespace ts {
                     }
                     return false;
                 }
+                if (isReadonlyArrayType(source) && isArrayType(target) && isReadonlyArrayType(target)) {
+                    if (reportErrors) {
+                        reportError(Diagnostics.The_type_0_is_readonly_and_is_incompatible_with_type_1, typeToString(source), typeToString(target));
+                    }
+                    return false;
+                }
                 return true;
             }
 
@@ -36260,4 +36273,4 @@ namespace ts {
         return !!(s.flags & SignatureFlags.HasLiteralTypes);
     }
 
-}
+}

src/compiler/diagnosticMessages.json

@@ -3148,6 +3148,10 @@
         "category": "Error",
         "code": 4110
     },
+    "The type '{0}' is 'readonly' and is incompatible with type '{1}'.": {
+        "category": "Error",
+        "code": 4111
+    },
 
     "The current host does not support the '{0}' option.": {
         "category": "Error",

tests/baselines/reference/readOnlyArrayAndTuplesAssignmentElaboration.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts(4,7): error TS4111: The type 'readonly [0]' is 'readonly' and is incompatible with type 'readonly []'.
+  Types of property 'length' are incompatible.
+    Type '1' is not assignable to type '0'.
+tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts(5,7): error TS4111: The type 'readonly [0]' is 'readonly' and is incompatible with type 'readonly [1]'.
+  Type '0' is not assignable to type '1'.
+
+
+==== tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts (2 errors) ====
+    // @strict
+    // #Repro from #35060
+
+    const x: readonly [] = null! as readonly [0];
+          ~
+!!! error TS4111: The type 'readonly [0]' is 'readonly' and is incompatible with type 'readonly []'.
+!!! error TS4111:   Types of property 'length' are incompatible.
+!!! error TS4111:     Type '1' is not assignable to type '0'.
+    const y: readonly [1] = null! as readonly [0];
+          ~
+!!! error TS4111: The type 'readonly [0]' is 'readonly' and is incompatible with type 'readonly [1]'.
+!!! error TS4111:   Type '0' is not assignable to type '1'.
+

tests/baselines/reference/readOnlyArrayAndTuplesAssignmentElaboration.js

@@ -0,0 +1,13 @@
+//// [readOnlyArrayAndTuplesAssignmentElaboration.ts]
+// @strict
+// #Repro from #35060
+
+const x: readonly [] = null! as readonly [0];
+const y: readonly [1] = null! as readonly [0];
+
+
+//// [readOnlyArrayAndTuplesAssignmentElaboration.js]
+// @strict
+// #Repro from #35060
+var x = null;
+var y = null;

tests/baselines/reference/readOnlyArrayAndTuplesAssignmentElaboration.symbols

@@ -0,0 +1,10 @@
+=== tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts ===
+// @strict
+// #Repro from #35060
+
+const x: readonly [] = null! as readonly [0];
+>x : Symbol(x, Decl(readOnlyArrayAndTuplesAssignmentElaboration.ts, 3, 5))
+
+const y: readonly [1] = null! as readonly [0];
+>y : Symbol(y, Decl(readOnlyArrayAndTuplesAssignmentElaboration.ts, 4, 5))
+

tests/baselines/reference/readOnlyArrayAndTuplesAssignmentElaboration.types

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts ===
+// @strict
+// #Repro from #35060
+
+const x: readonly [] = null! as readonly [0];
+>x : readonly []
+>null! as readonly [0] : readonly [0]
+>null! : null
+>null : null
+
+const y: readonly [1] = null! as readonly [0];
+>y : readonly [1]
+>null! as readonly [0] : readonly [0]
+>null! : null
+>null : null
+

tests/cases/compiler/readOnlyArrayAndTuplesAssignmentElaboration.ts

@@ -0,0 +1,5 @@
+// @strict
+// #Repro from #35060
+
+const x: readonly [] = null! as readonly [0];
+const y: readonly [1] = null! as readonly [0];