fix(compiler-core): adjacent v-else should cause a compiler error

[linzhe141]

close #13698

Summary by CodeRabbit

• Bug Fixes

  • Improved error handling for templates with consecutive v-else branches by displaying a clear error when two v-else directives are placed adjacent to each other without an intervening v-if.

• Tests

  • Added a new test case to verify that an appropriate error is triggered for adjacent v-else branches.

[coderabbitai]

Walkthrough

A validation check was added to the compiler's processIf function to detect and report an error when multiple adjacent v-else directives follow a v-if. A corresponding test case was introduced to verify that the error is triggered with the correct code and location when this invalid syntax is encountered.

Changes

File(s)	Change Summary
packages/compiler-core/src/transforms/vIf.ts	Added logic to detect consecutive v-else branches and emit a specific compiler error.
packages/compiler-core/tests/transforms/vIf.spec.ts	Added a test case to assert that an error is reported for adjacent v-else directives.

Sequence Diagram(s)

sequenceDiagram
    participant Template as Template Parser
    participant Compiler as Compiler (processIf)
    participant ErrorHandler as Error Handler

    Template->>Compiler: Parse nodes with v-if, v-else, v-else
    Compiler->>Compiler: Detects adjacent v-else branches
    Compiler->>ErrorHandler: Emit X_V_ELSE_NO_ADJACENT_IF error

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested labels

ready to merge, scope: compiler

Poem

🐇
In the garden of code, where logic does dwell,
Two v-else in a row now trigger a bell.
The compiler alerts, no more silent surprise,
With tests to ensure that no bug hides or lies.
Hop, hop, hooray—clean templates prevail!

Note

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📥 Commits

Reviewing files that changed from the base of the PR and between 28f135f and cc15a67.

📒 Files selected for processing (1)

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

🚧 Files skipped from review as they are similar to previous changes (1)

• packages/compiler-core/src/transforms/vIf.ts

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[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB	38.4 kB	34.6 kB
vue.global.prod.js	159 kB (+19 B)	58.6 kB (+6 B)	52.1 kB (-47 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.6 kB	18.2 kB	16.7 kB
createApp	54.6 kB	21.2 kB	19.4 kB
createSSRApp	58.8 kB	23 kB	20.9 kB
defineCustomElement	59.6 kB	22.8 kB	20.8 kB
overall	68.7 kB	26.4 kB	24.1 kB

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commit: cc15a67