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29 lines
2.6 KiB
Markdown
29 lines
2.6 KiB
Markdown
[//]: # (title: Syntax Errors)
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<!-- Copyright 2000-2022 JetBrains s.r.o. and other contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file. -->
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The IntelliJ Platform provides a mechanism for analyzing the PSI tree and highlighting syntax errors out of the box.
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While the PSI tree for the code is being built, a parser tries to consume tokens according to language grammar. When it encounters a syntax error, like an unexpected token, a [`PsiErrorElement`](upsource:///platform/core-api/src/com/intellij/psi/PsiErrorElement.java) is created and added to the PSI tree with an appropriate error description.
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In the code analysis daemon, the IntelliJ Platform visits every PSI element in the tree, and when a `PsiErrorElement` is encountered, information about it is collected and used while highlighting the code in the editor.
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## Controlling Syntax Errors Highlighting
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In some cases highlighting syntax errors is insufficient or even unnecessary:
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- An error can be presented to the user in an easier-to-understand way.
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- The actual error cause is in a different location in the code, which is not easily visible when looking at the syntax error.
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- An error can be safely ignored in a given context, e.g. incomplete code fragment injected in a Markdown code block.
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- A syntax error is not critical and can be considered as a warning or even information.
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The IntelliJ Platform allows plugins to disable highlighting particular syntax errors. These errors can be optionally handled by additional Annotators or [Inspections](code_inspections.md) if needed.
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To control which `PsiErrorElement`s should be reported and which can be ignored, a plugin has to provide implementation of [`HighlightErrorFilter`](upsource:///platform/analysis-api/src/com/intellij/codeInsight/highlighting/HighlightErrorFilter.java) and register it in the `com.intellij.highlightErrorFilter` extension point.
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The `HighlightErrorFilter` class contains a single abstract method `shouldHighlightErrorElement()` which should return false if a given `PsiErrorElement` should not be highlighted in the editor.
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**Examples:**
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- [`HtmlClosingTagErrorFilter`](upsource:///xml/xml-analysis-impl/src/com/intellij/codeInsight/highlighting/HtmlClosingTagErrorFilter.java) ignoring unmatched closing tag in HTML files
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- [`CodeFenceHighlightErrorFilter`](upsource:///plugins/markdown/src/org/intellij/plugins/markdown/injection/MarkdownCodeFenceErrorHighlightingIntention.kt) ignoring all syntax errors in a code injected into a Markdown code blocks
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**See also:**
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- [Controlling Highlighting](controlling_highlighting.md)
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