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Port "Account for right operands & fix a weird error message for leftmost nullish literals in checkNullishCoalesceOperands" #1805

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Merged
merged 1 commit into from
Oct 5, 2025
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Port "Account for right operands & fix a weird error message for leftmost nullish literals in checkNullishCoalesceOperands" #1805

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29 changes: 22 additions & 7 deletions internal/checker/checker.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12399,17 +12399,32 @@ func (c *Checker) checkNullishCoalesceOperands(left *ast.Node, right *ast.Node)
if ast.IsBinaryExpression(right) && ast.IsLogicalBinaryOperator(right.AsBinaryExpression().OperatorToken.Kind) {
c.grammarErrorOnNode(right, diagnostics.X_0_and_1_operations_cannot_be_mixed_without_parentheses, scanner.TokenToString(right.AsBinaryExpression().OperatorToken.Kind), scanner.TokenToString(ast.KindQuestionQuestionToken))
}
c.checkNullishCoalesceOperandLeft(left)
c.checkNullishCoalesceOperandRight(right)
}

func (c *Checker) checkNullishCoalesceOperandLeft(left *ast.Node) {
leftTarget := ast.SkipOuterExpressions(left, ast.OEKAll)
nullishSemantics := c.getSyntacticNullishnessSemantics(leftTarget)
if nullishSemantics != PredicateSemanticsSometimes {
if left.Parent.Parent.Kind == ast.KindBinaryExpression {
c.error(leftTarget, diagnostics.This_binary_expression_is_never_nullish_Are_you_missing_parentheses)
if nullishSemantics == PredicateSemanticsAlways {
c.error(leftTarget, diagnostics.This_expression_is_always_nullish)
} else {
if nullishSemantics == PredicateSemanticsAlways {
c.error(leftTarget, diagnostics.This_expression_is_always_nullish)
} else {
c.error(leftTarget, diagnostics.Right_operand_of_is_unreachable_because_the_left_operand_is_never_nullish)
}
c.error(leftTarget, diagnostics.Right_operand_of_is_unreachable_because_the_left_operand_is_never_nullish)
}
}
}

func (c *Checker) checkNullishCoalesceOperandRight(right *ast.Node) {
binaryExpression := right.Parent
if binaryExpression.Parent != nil && ast.IsBinaryExpression(binaryExpression.Parent) && binaryExpression.Parent.AsBinaryExpression().OperatorToken.Kind == ast.KindQuestionQuestionToken {
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Is retaining isNotWithinNullishCoalesceExpression too annoying?

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it's not like super annoying, but it's a rather straightforward check and it was only used in this single place so I decided to inline it

rightTarget := ast.SkipOuterExpressions(right, ast.OEKAll)
nullishSemantics := c.getSyntacticNullishnessSemantics(rightTarget)
switch nullishSemantics {
case PredicateSemanticsAlways:
c.error(rightTarget, diagnostics.This_expression_is_always_nullish)
case PredicateSemanticsNever:
c.error(rightTarget, diagnostics.This_expression_is_never_nullish)
}
}
}
Expand Down
66 changes: 51 additions & 15 deletions testdata/baselines/reference/submodule/compiler/predicateSemantics.errors.txt
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Expand Up @@ -6,15 +6,27 @@ predicateSemantics.ts(28,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(29,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(30,13): error TS2872: This kind of expression is always truthy.
predicateSemantics.ts(31,13): error TS2872: This kind of expression is always truthy.
predicateSemantics.ts(32,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(33,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(34,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(32,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(32,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(33,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(34,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(34,22): error TS2871: This expression is always nullish.
predicateSemantics.ts(36,20): error TS2871: This expression is always nullish.
predicateSemantics.ts(37,20): error TS2871: This expression is always nullish.
predicateSemantics.ts(38,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(39,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(40,21): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(45,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(46,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(47,13): error TS2870: This binary expression is never nullish. Are you missing parentheses?
predicateSemantics.ts(40,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(40,29): error TS2871: This expression is always nullish.
predicateSemantics.ts(41,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(42,20): error TS2881: This expression is never nullish.
predicateSemantics.ts(43,21): error TS2881: This expression is never nullish.
predicateSemantics.ts(45,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(45,21): error TS2871: This expression is always nullish.
predicateSemantics.ts(45,29): error TS2871: This expression is always nullish.
predicateSemantics.ts(46,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(46,21): error TS2881: This expression is never nullish.
predicateSemantics.ts(47,13): error TS2871: This expression is always nullish.
predicateSemantics.ts(47,22): error TS2881: This expression is never nullish.
predicateSemantics.ts(50,8): error TS2872: This kind of expression is always truthy.
predicateSemantics.ts(51,11): error TS2872: This kind of expression is always truthy.
predicateSemantics.ts(52,8): error TS2872: This kind of expression is always truthy.
Expand All @@ -26,7 +38,7 @@ predicateSemantics.ts(89,1): error TS2869: Right operand of ?? is unreachable be
predicateSemantics.ts(90,1): error TS2869: Right operand of ?? is unreachable because the left operand is never nullish.


==== predicateSemantics.ts (26 errors) ====
==== predicateSemantics.ts (38 errors) ====
declare let opt: number | undefined;

// OK: One or other operand is possibly nullish
Expand Down Expand Up @@ -76,16 +88,24 @@ predicateSemantics.ts(90,1): error TS2869: Right operand of ?? is unreachable be
!!! error TS2872: This kind of expression is always truthy.
const p07 = null ?? null ?? null;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~~~~
!!! error TS2871: This expression is always nullish.
const p08 = null ?? opt ?? null;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
const p09 = null ?? (opt ? null : undefined) ?? null;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2871: This expression is always nullish.

const p10 = opt ?? null ?? 1;
~~~~
!!! error TS2871: This expression is always nullish.
const p11 = opt ?? null ?? null;
~~~~
!!! error TS2871: This expression is always nullish.
const p12 = opt ?? (null ?? 1);
~~~~
!!! error TS2871: This expression is always nullish.
Expand All @@ -94,20 +114,36 @@ predicateSemantics.ts(90,1): error TS2869: Right operand of ?? is unreachable be
!!! error TS2871: This expression is always nullish.
const p14 = opt ?? (null ?? null ?? null);
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~~~~
!!! error TS2871: This expression is always nullish.
const p15 = opt ?? (opt ? null : undefined) ?? null;
~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2871: This expression is always nullish.
const p16 = opt ?? 1 ?? 2;
~
!!! error TS2881: This expression is never nullish.
const p17 = opt ?? (opt ? 1 : 2) ?? 3;
~~~~~~~~~~~
!!! error TS2881: This expression is never nullish.

const p21 = null ?? null ?? null ?? null;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~~~~
!!! error TS2871: This expression is always nullish.
~~~~
!!! error TS2871: This expression is always nullish.
const p22 = null ?? 1 ?? 1;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~
!!! error TS2881: This expression is never nullish.
const p23 = null ?? (opt ? 1 : 2) ?? 1;
~~~~
!!! error TS2870: This binary expression is never nullish. Are you missing parentheses?
!!! error TS2871: This expression is always nullish.
~~~~~~~~~~~
!!! error TS2881: This expression is never nullish.

// Outer expression tests
while ({} as any) { }
Expand Down
115 changes: 0 additions & 115 deletions testdata/baselines/reference/submodule/compiler/predicateSemantics.errors.txt.diff
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