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Better assignability errors to never-producing vacuous intersections #37618

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Better assignability errors to never-producing vacuous intersections #37618

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0d7a75e
Added test case.
DanielRosenwasser Mar 26, 2020
eedc389
Better assignability errors when the target is an intersection that g…
DanielRosenwasser Mar 26, 2020
13269b3
Accepted baselines.
DanielRosenwasser Mar 26, 2020
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12 changes: 11 additions & 1 deletion src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4102,7 +4102,9 @@ namespace ts {
return undefined!; // TODO: GH#18217
}

type = getReducedType(type);
if (!(context.flags & NodeBuilderFlags.PreserveVacuousIntersections)) {
type = getReducedType(type);
}

if (type.flags & TypeFlags.Any) {
context.approximateLength += 3;
Expand Down Expand Up @@ -15528,6 +15530,10 @@ namespace ts {
return result;
}
}
else if (getObjectFlags(originalTarget) & ObjectFlags.IsNeverIntersection) {
const intersectionString = typeToString(originalTarget, /*enclosingDeclaration*/ undefined, TypeFormatFlags.PreserveVacuousIntersections);
errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.The_type_never_was_reduced_from_the_intersection_0_Each_type_of_that_intersection_has_properties_that_conflict_so_values_of_that_type_can_never_exist, intersectionString);
}
if (!headMessage && maybeSuppress) {
lastSkippedInfo = [source, target];
// Used by, eg, missing property checking to replace the top-level message with a more informative one
Expand Down Expand Up @@ -24098,6 +24104,10 @@ namespace ts {
relatedInfo = suggestion.valueDeclaration && createDiagnosticForNode(suggestion.valueDeclaration, Diagnostics._0_is_declared_here, suggestedName);
}
else {
if (getObjectFlags(containingType) & ObjectFlags.IsNeverIntersection) {
const intersectionString = typeToString(containingType, /*enclosingDeclaration*/ undefined, TypeFormatFlags.PreserveVacuousIntersections);
errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.The_type_never_was_reduced_from_the_intersection_0_Each_type_of_that_intersection_has_properties_that_conflict_so_values_of_that_type_can_never_exist, intersectionString);
}
errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1, declarationNameToString(propNode), typeToString(containingType));
}
}
Expand Down
4 changes: 4 additions & 0 deletions src/compiler/diagnosticMessages.json
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Expand Up @@ -5653,5 +5653,9 @@
"An optional chain cannot contain private identifiers.": {
"category": "Error",
"code": 18030
},
"The type 'never' was reduced from the intersection '{0}'. Each type of that intersection has properties that conflict, so values of that type can never exist.": {
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why 'each' here? Wouldn't 'some' be correct?

If that's true, I'd just say "Types in that intersection ..."

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Good point

"category": "Error",
"code": 18031
}
}
4 changes: 3 additions & 1 deletion src/compiler/types.ts
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Expand Up @@ -3687,6 +3687,7 @@ namespace ts {
OmitParameterModifiers = 1 << 13, // Omit modifiers on parameters
UseAliasDefinedOutsideCurrentScope = 1 << 14, // Allow non-visible aliases
UseSingleQuotesForStringLiteralType = 1 << 28, // Use single quotes for string literal type
PreserveVacuousIntersections = 1 << 29, // uh oh...

// Error handling
AllowThisInObjectLiteral = 1 << 15,
Expand Down Expand Up @@ -3730,6 +3731,7 @@ namespace ts {

UseAliasDefinedOutsideCurrentScope = 1 << 14, // For a `type T = ... ` defined in a different file, write `T` instead of its value, even though `T` can't be accessed in the current scope.
UseSingleQuotesForStringLiteralType = 1 << 28, // Use single quotes for string literal type
PreserveVacuousIntersections = 1 << 29, // uh oh

// Error Handling
AllowUniqueESSymbolType = 1 << 20, // This is bit 20 to align with the same bit in `NodeBuilderFlags`
Expand All @@ -3749,7 +3751,7 @@ namespace ts {
NodeBuilderFlagsMask = NoTruncation | WriteArrayAsGenericType | UseStructuralFallback | WriteTypeArgumentsOfSignature |
UseFullyQualifiedType | SuppressAnyReturnType | MultilineObjectLiterals | WriteClassExpressionAsTypeLiteral |
UseTypeOfFunction | OmitParameterModifiers | UseAliasDefinedOutsideCurrentScope | AllowUniqueESSymbolType | InTypeAlias |
UseSingleQuotesForStringLiteralType,
UseSingleQuotesForStringLiteralType | PreserveVacuousIntersections,
}

export const enum SymbolFormatFlags {
Expand Down
4 changes: 3 additions & 1 deletion tests/baselines/reference/api/tsserverlibrary.d.ts
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Expand Up @@ -2136,6 +2136,7 @@ declare namespace ts {
OmitParameterModifiers = 8192,
UseAliasDefinedOutsideCurrentScope = 16384,
UseSingleQuotesForStringLiteralType = 268435456,
PreserveVacuousIntersections = 536870912,
AllowThisInObjectLiteral = 32768,
AllowQualifedNameInPlaceOfIdentifier = 65536,
AllowAnonymousIdentifier = 131072,
Expand Down Expand Up @@ -2164,6 +2165,7 @@ declare namespace ts {
OmitParameterModifiers = 8192,
UseAliasDefinedOutsideCurrentScope = 16384,
UseSingleQuotesForStringLiteralType = 268435456,
PreserveVacuousIntersections = 536870912,
AllowUniqueESSymbolType = 1048576,
AddUndefined = 131072,
WriteArrowStyleSignature = 262144,
Expand All @@ -2172,7 +2174,7 @@ declare namespace ts {
InFirstTypeArgument = 4194304,
InTypeAlias = 8388608,
/** @deprecated */ WriteOwnNameForAnyLike = 0,
NodeBuilderFlagsMask = 277904747
NodeBuilderFlagsMask = 814775659
}
export enum SymbolFormatFlags {
None = 0,
Expand Down
4 changes: 3 additions & 1 deletion tests/baselines/reference/api/typescript.d.ts
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Expand Up @@ -2136,6 +2136,7 @@ declare namespace ts {
OmitParameterModifiers = 8192,
UseAliasDefinedOutsideCurrentScope = 16384,
UseSingleQuotesForStringLiteralType = 268435456,
PreserveVacuousIntersections = 536870912,
AllowThisInObjectLiteral = 32768,
AllowQualifedNameInPlaceOfIdentifier = 65536,
AllowAnonymousIdentifier = 131072,
Expand Down Expand Up @@ -2164,6 +2165,7 @@ declare namespace ts {
OmitParameterModifiers = 8192,
UseAliasDefinedOutsideCurrentScope = 16384,
UseSingleQuotesForStringLiteralType = 268435456,
PreserveVacuousIntersections = 536870912,
AllowUniqueESSymbolType = 1048576,
AddUndefined = 131072,
WriteArrowStyleSignature = 262144,
Expand All @@ -2172,7 +2174,7 @@ declare namespace ts {
InFirstTypeArgument = 4194304,
InTypeAlias = 8388608,
/** @deprecated */ WriteOwnNameForAnyLike = 0,
NodeBuilderFlagsMask = 277904747
NodeBuilderFlagsMask = 814775659
}
export enum SymbolFormatFlags {
None = 0,
Expand Down
12 changes: 10 additions & 2 deletions tests/baselines/reference/intersectionReduction.errors.txt
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@@ -1,9 +1,12 @@
tests/cases/conformance/types/intersection/intersectionReduction.ts(38,4): error TS2339: Property 'kind' does not exist on type 'never'.
tests/cases/conformance/types/intersection/intersectionReduction.ts(80,1): error TS2322: Type 'any' is not assignable to type 'never'.
The type 'never' was reduced from the intersection 'A & B'. Each type of that intersection has properties that conflict, so values of that type can never exist.
tests/cases/conformance/types/intersection/intersectionReduction.ts(39,1): error TS2322: Type '42' is not assignable to type 'never'.
The type 'never' was reduced from the intersection 'A & B'. Each type of that intersection has properties that conflict, so values of that type can never exist.
tests/cases/conformance/types/intersection/intersectionReduction.ts(81,1): error TS2322: Type 'any' is not assignable to type 'never'.
tests/cases/conformance/types/intersection/intersectionReduction.ts(82,1): error TS2322: Type 'any' is not assignable to type 'never'.


==== tests/cases/conformance/types/intersection/intersectionReduction.ts (3 errors) ====
==== tests/cases/conformance/types/intersection/intersectionReduction.ts (4 errors) ====
declare const sym1: unique symbol;
declare const sym2: unique symbol;

Expand Down Expand Up @@ -44,6 +47,11 @@ tests/cases/conformance/types/intersection/intersectionReduction.ts(81,1): error
ab.kind; // Error
~~~~
!!! error TS2339: Property 'kind' does not exist on type 'never'.
!!! error TS2339: The type 'never' was reduced from the intersection 'A & B'. Each type of that intersection has properties that conflict, so values of that type can never exist.
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You should probably search for and report the properties that conflict and their respective types, no? So the error is somewhat more actionable?

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Definitely seems doable, but only if the approach in this PR seems reasonable.

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Seems OK. We could probably consider leaving behind more "breadcrumbs" like this in the future to explain how a specific type came about; but it's always about striking that balance between useful explaianation and terseness.

ab = 42;
~~
!!! error TS2322: Type '42' is not assignable to type 'never'.
!!! error TS2322: The type 'never' was reduced from the intersection 'A & B'. Each type of that intersection has properties that conflict, so values of that type can never exist.

declare let x: A | (B & C); // A
let a: A = x;
Expand Down
2 changes: 2 additions & 0 deletions tests/baselines/reference/intersectionReduction.js
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Expand Up @@ -37,6 +37,7 @@ type C = { kind: 'c', foo: number };

declare let ab: A & B;
ab.kind; // Error
ab = 42;

declare let x: A | (B & C); // A
let a: A = x;
Expand Down Expand Up @@ -111,6 +112,7 @@ const f4 = (t: number | (Container<"b"> & { dataB: boolean } & Container<"a">)):

//// [intersectionReduction.js]
ab.kind; // Error
ab = 42;
var a = x;
var r1 = f10(a1); // unknown
var r2 = f10(a2); // string
Expand Down
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