fix(compiler): using guard instead of non-nullish assertion

[ShenQingchuan]

Description

core/packages/compiler-core/src/transforms/transformVBindShorthand.ts

Line 20 in 079010a

const arg = prop.arg!

This non-nullish assertion is harmful that it will be broken on language service when user has only typed : on an element, in that case we shouldn't treat the single : as a VBindShorthand

We got error thrown below

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'type')
    at Array.yX (index-C2PqwR5h.js:108:3591)
    at bS (index-C2PqwR5h.js:91:9055)
    at iRe (index-C2PqwR5h.js:91:8941)
    at bS (index-C2PqwR5h.js:91:9320)

How to reproduce

https://play.vuejs.org/#eNp9UbFOwzAQ/ZXDS5cmGWCKIiRAHWAoCDp6CcnRpCS2ZV/SoCoDCz/Awsa/8QV8AudEbTqgDrZ8997zvWfvxJUxYdugiEXiMlsaAofUmEupogiWmopSrcMwhN/vr3epkmgkMcwFYW2qlJArgOQsCODn4xNWbwYhBcfCCmEWz+AZK72F1EFKZCEIJj6sClSgDW+ZVk6zwCECFX5ZvcUc0Fo9ifKyhRgiLpLoaLyYC3J8w0u5DjdOK46z83wpMl2bskJ7b6jkCVLEMCAeSyv2dTf0yDY43/ezArPXf/ob1/meFA8WHdoWpThglNo10ggvnpbY8fkA1jpvKmafAB+R0zfe40i7blTOto94g9vb2mhL/LQrt+gIlduH8kY9sx/4UvCf3pyIPtk9Dy8GnVS96P8Ayt+tIA==

Summary by CodeRabbit

• Bug Fixes

  • Corrected handling of v-bind same-name shorthand to require a non-empty argument, preventing accidental matches and reducing false positives.
  • Improved compile-time stability by safely processing arguments only when present.
  • Aligned error reporting for invalid shorthand arguments with existing behaviors for clearer, consistent messages.

• Developer Experience

  • More predictable template compilation in edge cases involving v-bind shorthand, reducing confusion and unexpected warnings.

[coderabbitai]

Walkthrough

Tightens v-bind shorthand processing in transformVBindShorthand by requiring a non-empty directive argument when handling same-name shorthand. The condition now checks both missing expression and presence of arg, and uses arg directly when present, aligning invalid-arg error reporting with existing logic.

Changes

Cohort / File(s)	Summary of Edits
Compiler v-bind shorthand handling packages/compiler-core/src/transforms/transformVBindShorthand.ts	Updated condition to require both no expression and a present arg for same-name shorthand; replaced non-null assertion on arg with direct access; relies on existing error path for invalid arg types.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor Dev as Template Author
  participant P as Parser
  participant T as transformVBindShorthand
  participant E as ErrorReporter

  Dev->>P: Uses v-bind shorthand (e.g., :foo or :)
  P->>T: Directive node (prop) with arg/exp
  T->>T: Check: !prop.exp AND prop.arg
  alt arg present and exp missing
    T->>T: Treat as same-name shorthand using arg
  else arg missing or invalid
    T->>E: Report X_V_BIND_INVALID_SAME_NAME_ARGUMENT
  end

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• refactor(compiler): add separate transform for vbind shorthand #13438 — Previously moved v-bind shorthand handling into transformVBindShorthand and removed the older path; this PR further tightens that logic.

Suggested labels

scope: compiler, :hammer: p3-minor-bug

Suggested reviewers

• sxzz
• baiwusanyu-c
• KazariEX

Poem

I nibble at args with careful delight,
A colon’s whisper, now parsed just right.
When exp is empty and names align,
I hop to the shorthand, a tidy sign.
If arg goes missing—thump!—I warn,
Then bound I am to code well-worn. 🐇✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title succinctly and accurately describes the main change—replacing the non-nullish assertion with a guard in the compiler transform—and follows the conventional commit style used in the repository.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 079010a and 5f4825e.

📒 Files selected for processing (1)

• packages/compiler-core/src/transforms/transformVBindShorthand.ts (1 hunks)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (3)

• GitHub Check: Redirect rules
• GitHub Check: Header rules
• GitHub Check: Pages changed

🔇 Additional comments (2)

packages/compiler-core/src/transforms/transformVBindShorthand.ts (2)

18-19: LGTM! Guard prevents runtime error on malformed input.

Adding prop.arg to the condition correctly ensures the argument exists before processing. This prevents the "Cannot read properties of undefined (reading 'type')" error when a user types only ":" in the template, as described in the PR.

---

21-21: LGTM! Assertion removal is safe with the guard.

Removing the non-null assertion operator is correct since the guard on line 19 ensures prop.arg is truthy before reaching this line. TypeScript's control flow analysis will narrow the type automatically.

---

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[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	102 kB	38.6 kB	34.8 kB
vue.global.prod.js	160 kB (+7 B)	58.7 kB (+4 B)	52.2 kB (-9 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.7 kB	18.3 kB	16.7 kB
createApp	54.7 kB	21.3 kB	19.5 kB
createSSRApp	58.9 kB	23 kB	21 kB
defineCustomElement	60 kB	23 kB	21 kB
overall	68.8 kB	26.5 kB	24.2 kB

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commit: 5f4825e