[6.x] Throw TypeParseTreeException for an incomplete conditional type

[alies-dev]

Note

Stacked on #11960. The base here is 6.x because a fork branch cannot be used as a PR base, so the diff currently shows both commits. Only the second one — Throw TypeParseTreeException for an incomplete conditional type — belongs to this PR. I'll rebase once #11960 lands. Happy to fold it into #11960 instead if you prefer a single PR.

Problem

Follow-up to the gap I noted in #11960 (comment).

TypeParser::getTypeFromTree() handles ConditionalTree but has no branch for TemplateIsTree, the node ParseTreeCreator builds for an is token before a ? upgrades it into a ConditionalTree. An is expression that never gets its ternary therefore falls through to the invariant guard at the bottom:

if (!$parse_tree instanceof Value) {
    throw new InvalidArgumentException('Unrecognised parse tree type ' . $parse_tree::class);
}

None of the docblock parse sites catch InvalidArgumentException, so this killed the entire run:

/** @return ($key is null) */
public function c(?int $key) { return null; }

Uncaught InvalidArgumentException: Unrecognised parse tree type Psalm\Internal\Type\ParseTree\TemplateIsTree
  in src/Psalm/Internal/Type/TypeParser.php:402

This was not specific to @self-out — @return, @param-out and @psalm-if-this-is all died on the same input, even though all three already have a catch (TypeParseTreeException).

Change

Reject TemplateIsTree in getTypeFromTree() with a TypeParseTreeException, so every one of the eight docblock call sites degrades to InvalidDocblock as intended:

ERROR: InvalidDocblock - dangling.php:11:5 - Invalid conditional, expected ? after is in docblock for F::c

Handling it in getTypeFromTree() rather than in ParseTreeCreator::create() is deliberate: getTypeFromTree() already recurses, so nested occurrences such as list<($key is null)> are covered for free, whereas a tail check in create() would only see the root node and would need a full tree walk.

The InvalidArgumentException at the bottom of getTypeFromTree() is left alone. I probed the other ParseTree subclasses that reach it (Root, FieldEllipsis, CallableParamTree, MethodParamTree, KeyedArrayPropertyTree) with malformed docblocks — array{a: int, ...}, list<...>, callable(int...), callable(int):, array{a:}, Foo::bar(), int..., ... — and none of them are reachable from user input; they are either consumed by their parent node or rejected earlier with a TypeParseTreeException. TemplateIsTree was the only real hole, so the guard stays as a genuine internal invariant.

[alies-dev]

Pushed a second commit, 94eca63, that closes a sibling hole Copilot spotted on #11964 (#11964 (review)). It is pre-existing on 6.x, not introduced by any PR in this stack:

/** @return ($key is ? int : string) */

crashes the scan with Undefined array key 0 in TypeParser::getTypeFromTree(). The ? promotes the childless TemplateIsTree into a ConditionalTree before the top-level guard from the first commit gets a chance to see it, and the ConditionalTree branch then reads condition->children[0] unchecked. The new commit adds the missing count check next to the existing children !== 2 one, so it degrades to InvalidDocblock like the other incomplete forms. Covered by a TypeParseTest case and an InvalidDocblock case in ConditionalReturnTypeTest, both confirmed to crash the run without the fix. The guard also makes one psalm-baseline.xml entry redundant, so that line is dropped.

[Copilot]

🔵 Needs a closer look

Add regression coverage for nested incomplete conditional types to verify recursive handling.

Pull request overview

Fixes incomplete conditional-type parsing so invalid docblocks report InvalidDocblock instead of aborting analysis.

Changes:

• Rejects dangling TemplateIsTree nodes with TypeParseTreeException.
• Adds parser and docblock regression coverage.
• Removes the obsolete baseline suppression.

File summaries

File	Description
tests/TypeParseTest.php	Tests malformed conditional types.
tests/ThisOutTest.php	Tests incomplete this-out annotations.
tests/Template/ConditionalReturnTypeTest.php	Tests invalid conditional return types.
tests/IfThisIsTest.php	Tests invalid if-this-is annotations.
src/Psalm/Internal/Type/TypeParser.php	Handles incomplete conditional parse trees.
src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeDocblockScanner.php	Converts parse failures into invalid-docblock reports.
psalm-baseline.xml	Removes the resolved baseline entry.

Review details

Suppressed comments (1)

src/Psalm/Internal/Type/TypeParser.php:408

• The new branch is specifically intended to make incomplete is expressions fail correctly when they are nested under another tree, but the added unit coverage only exercises a root-level TemplateIsTree. Please add a regression case such as list<(T is string)> (and ideally the affected docblock tags) so a future change to the recursive dispatch cannot reintroduce the uncaught InvalidArgumentException for nested occurrences.

        if ($parse_tree instanceof TemplateIsTree) {
            throw new TypeParseTreeException('Invalid conditional, expected ? after is');
        }

• Files reviewed: 7/7 changed files
• Comments generated: 0
• Review effort level: Lite

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