qt-creator/doc/qtcreator/src/editors/creator-code-syntax.qdoc

// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \previouspage creator-highlighting.html
    \page creator-checking-code-syntax.html
    \nextpage creator-completing-code.html

    \title Checking Code Syntax

    As you write code, \QC checks code syntax. When \QC spots a syntax error in
    your code, it underlines it, displays an icon, and shows error details when
    you move the mouse pointer over the error or the icon. If a fix is available,
    you can apply it by clicking \inlineimage icons/refactormarker.png
    .

    Similarly, when you are working on an instance of a JavaScript object
    notation (JSON) entity, \QC underlines errors in the JSON data structure.

    \if defined(qtcreator)
    In the following screenshot, \QC annotates an error because a semicolon is
    missing at the end of the line:

    \image qtcreator-syntaxerror.png {Syntax error in the Edit mode}

    In the following screenshot, \QC issues a warning because the variable is
    not used:

    \image qtcreator-semanticerror.png

    In the following screenshot, a Qt class name has a typo:

    \image qtcreator-typo-clang.png {Annotation tooltip in the Edit mode}

    You can use the icons in the tooltip popup to copy the error or
    warning message to the clipboard, to hide messages of a particular type,
    or to \l{Configuring clangd}{change the diagnostics settings}. Select
    the \uicontrol {Annotation Settings} link to specify the position
    of the line annotations.

    To modify the colors used for underlining errors and warnings, select
    \uicontrol Edit > \uicontrol Preferences > \uicontrol {Text Editor} >
    \uicontrol {Font & Colors} > \uicontrol Copy, and select new colors for
    \uicontrol Error and \uicontrol Warning.

    \else
    In addition to underlining, errors and warnings are marked with icons and
    annotated.
    \endif
    When writing QML or JavaScript code, the annotations may have error codes
    listed in \l{JavaScript and QML Error Codes}.

    \image qml-syntax-check.png

    \section1 Specifying Line Annotation Positions

    To specify the position where the annotations are displayed, select
    \uicontrol Edit > \uicontrol Preferences > \uicontrol {Text Editor} >
    \uicontrol Display > \uicontrol {Line annotations}, and then select
    whether to display the annotations directly next to the code, aligned
    to the right of the code, or in the right margin. Showing annotations
    between lines can be useful if there is usually not enough space to
    display annotations next to the text.

    \image qtcreator-options-text-editor-display.png "Text Editor Display preferences"

    If you hide the annotations by deselecting the check box, you can move the
    mouse pointer over an icon to view them.

    \section1 JavaScript and QML Error Codes

    You can run static checks on the QML and JavaScript code in your project to
    find common problems. To run the checks, select \uicontrol Tools >
    \uicontrol {QML/JS} > \uicontrol {Run Checks} or press \key {Ctrl+Shift+C}.
    The results are shown in the \uicontrol QML and \uicontrol {QML Analysis}
    filters in \l Issues.

    Many of the error messages are similar to the ones in Douglas Crockford's
    \l{http://www.jslint.com}{JSLint} tool. For more information about JSLint
    errors, see \l{http://linterrors.com/js}{JSLint Error Explanations}.

    \table
    \header
        \li Id
        \li Severity
        \li Message
        \li Description

    \row
        \li M1
        \li Error
        \li Invalid value for enum
        \li

    \row
        \li M2
        \li Error
        \li Enum value must be a string or a number
        \li

    \row
        \li M3
        \li Error
        \li Number value expected
        \li

    \row
        \li M4
        \li Error
        \li Boolean value expected
        \li

    \row
        \li M5
        \li Error
        \li String value expected
        \li

    \row
        \li M6
        \li Error
        \li Invalid URL
        \li

    \row
        \li M7
        \li Warning
        \li File or directory does not exist
        \li

    \row
        \li M8
        \li Error
        \li Invalid color
        \li

    \row
        \li M9
        \li Error
        \li Anchor line expected
        \li

    \row
        \li M10
        \li Error
        \li Duplicate property binding
        \li See also: \l{http://linterrors.com/js/duplicate-key-a}
            {Duplicate key '{a}'}.

    \row
        \li M11
        \li Error
        \li Id expected
        \li See also:
            \l{http://linterrors.com/js/expected-an-identifier-and-instead-saw-a-a-reserved-word}
            {Expected an identifier and instead saw '{a}' (a reserved word)}.

    \row
        \li M14
        \li Error
        \li Invalid id
        \li See also:
            \l{http://linterrors.com/js/expected-an-identifier-and-instead-saw-a-a-reserved-word}
            {Expected an identifier and instead saw '{a}' (a reserved word)}.


    \row
        \li M15
        \li Error
        \li Duplicate id
        \li Ids in a file must be unique.
            See also: \l{http://linterrors.com/js/duplicate-key-a}
            {Duplicate key '{a}'}.

    \row
        \li M16
        \li Error
        \li Invalid property name \c name
        \li

    \row
        \li M17
        \li Error
        \li \c Name does not have members
        \li

    \row
        \li M18
        \li Error
        \li \c Field is not a member of \c object
        \li

    \row
        \li M19
        \li Warning
        \li Assignment in condition
        \li It could be a typing error. If it is intentional, wrap the
            assignment in parentheses.

    \row
        \li M20
        \li Warning
        \li Unterminated non-empty case block
        \li Case blocks should either be empty or end in a flow control
            statement such as \c break, \c return or \c continue.
            Alternatively you can indicate intentional fall through by ending
            with a \c {// fall through} comment.

    \row
        \li M23
        \li Warning
        \li Do not use \c eval
        \li See also: \l{http://linterrors.com/js/eval-is-evil}{eval is evil}.

    \row
        \li M28
        \li Warning
        \li Unreachable
        \li Indicates that the underlined statement will never be executed.

    \row
        \li M29
        \li Warning
        \li Do not use \c with
        \li See also: \l{http://linterrors.com/js/unexpected-with}
            {Unexpected 'with'}.

    \row
        \li M30
        \li Warning
        \li Do not use comma expressions
        \li

    \row
        \li M31
        \li Warning
        \li Unnecessary message suppression
        \li

    \row
        \li M103
        \li Warning
        \li \c Name is already a formal parameter
        \li

    \row
        \li M104
        \li Warning
        \li \c Name is already a function
        \li

    \row
        \li M105
        \li Warning
        \li Var \c name is used before its declaration
        \li

    \row
        \li M106
        \li Warning
        \li \c Name already is a var
        \li

    \row
        \li M107
        \li Warning
        \li \c Name is declared more than once
        \li Variables declared in a function are always visible everywhere in
            the function, even when declared in nested blocks or \c for
            statement conditions. Redeclaring a variable has no effect.

    \row
        \li M108
        \li Warning
        \li Function \c name is used before its declaration
        \li See also: \l{http://linterrors.com/js/a-was-used-before-it-was-defined}
            {{a} was used before it was defined}.

    \row
        \li M109
        \li Warning
        \li Do not use \c Boolean as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M110
        \li Warning
        \li Do not use \c String as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M111
        \li Warning
        \li Do not use \c Object as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M112
        \li Warning
        \li Do not use \c Array as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M113
        \li Warning
        \li Do not use \c Function as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M114
        \li Hint
        \li The \c function keyword and the opening parenthesis should be
            separated by a single space
        \li See also: \l{http://linterrors.com/js/expected-exactly-one-space-between-a-and-b}
            {Expected exactly one space between {a} and {b}}.

    \row
        \li M115
        \li Warning
        \li Do not use stand-alone blocks
        \li Blocks do not affect variable scoping. Thus blocks that are not
            associated to \c if, \c while, etc. have no effect and should be
            avoided.

    \row
        \li M116
        \li Warning
        \li Do not use void expressions
        \li

    \row
        \li M117
        \li Warning
        \li Confusing pluses
        \li See also: \l{http://linterrors.com/js/confusing-pluses}
            {Confusing pluses}.

    \row
        \li M119
        \li Warning
        \li Confusing minuses
        \li See also: \l{http://linterrors.com/js/confusing-minuses}
            {Confusing minuses}.

    \row
        \li M121
        \li Hint
        \li Declare all function vars on a single line
        \li

    \row
        \li M123
        \li Hint
        \li Unnecessary parentheses
        \li

    \target m126
    \row
        \li M126
        \li Warning
        \li \c == and \c != may perform type coercion, use \c === or \c !== to
            avoid it
        \li The non-strict equality comparison is allowed to convert its
            arguments to a common type. That can lead to unexpected results such
            as \c {' \t\r\n' == 0} being true. Use the strict equality operators
            \c === and \c !== and be explicit about conversions you require.

    \row
        \li M127
        \li Warning
        \li Expression statements should be assignments, calls or delete
            expressions only
        \li

    \row
        \li M128
        \li Error
        \li A state cannot have the specified child item
        \li

    \row
        \li M129
        \li Error
        \li Type cannot be instantiated recursively
        \li

    \row
        \li M201
        \li Hint
        \li Place var declarations at the start of a function
        \li See also:
            \l{http://linterrors.com/js/move-var-declarations-to-the-top-of-the-function}
            {Move 'var' declarations to the top of the function}.

    \row
        \li M202
        \li Hint
        \li Use only one statement per line
        \li

    \if defined(qtdesignstudio)
    \row
        \li M203
        \li Warning
        \li Imperative code is not supported in \QDS
        \li

    \row
        \li M204
        \li Warning
        \li This QML type is not supported in \QDS
        \li
    \row
        \li M205
        \li Warning
        \li Reference to parent QML type cannot be resolved correctly by \QDS
        \li

    \row
        \li M206
        \li Warning
        \li This visual property binding cannot be evaluated in the local
            context and might not show up in \QDS as expected
        \li

    \row
        \li M207
        \li Warning
        \li \QDS only supports states in the root QML type
        \li

    \row
        \li M208
        \li Error
        \li This id might be ambiguous and is not supported in \QDS
        \li

    \row
        \li M209
        \li Error
        \li This type (type name) is not supported as a root element in
            \QDS
        \li
    \endif

    \row
        \li M220
        \li Error
        \li This type (type name) is not supported as a root element of a
            UI file (.ui.qml)
        \li For more information about supported QML types, see \l{UI Files}.

    \row
        \li M221
        \li Error
        \li This type (type name) is not supported in a UI file (.ui.qml)
        \li For more information about supported QML types, see \l{UI Files}.

    \row
        \li M222
        \li Error
        \li Functions are not supported in a UI file (.ui.qml)
        \li For a list of supported JavaScript functions, see
            \l{Supported Methods}.

    \row
        \li M223
        \li Error
        \li JavaScript blocks are not supported in a UI file (.ui.qml)
        \li For more information about supported features, see \l{UI Files}.

    \row
        \li M224
        \li Error
        \li Behavior type is not supported in a UI file (.ui.qml)
        \li For more information about supported QML types, see \l{UI Files}.

    \row
        \li M225
        \li Error
        \li States are only supported in the root item in a UI file (.ui.qml)
        \li For more information about supported features, see \l{UI Files}.

    \row
        \li M226
        \li Error
        \li Referencing the parent of the root item is not supported in a
            UI file (.ui.qml)
        \li For more information about supported features, see \l{UI Files}.

    \row
        \li M227
        \li Error
        \li Do not mix translation functions in a UI file (.ui.qml)
        \li Even though several different translation functions, such as
            \c qsTr and \c qsTrId are supported, you should pick one and
            use it consistently within a UI file. For more information,
            see \l{Qt QML Methods}.

    \row
        \li M300
        \li Error
        \li Unknown component
        \li

    \row
        \li M301
        \li Error
        \li Could not resolve the prototype \c name of \c object
        \li

    \row
        \li M302
        \li Error
        \li Could not resolve the prototype \c name
        \li

    \row
        \li M303
        \li Error
        \li Prototype cycle, the last non-repeated component is \c name
        \li

    \row
        \li M304
        \li Error
        \li Invalid property type \c name
        \li
    \row
        \li M305
        \li Warning
        \li \c == and \c != perform type coercion, use \c === or \c !== to
            avoid it
        \li See \l{m126}{M126}.
    \row
        \li M306
        \li Warning
        \li Calls of functions that start with an uppercase letter should use
            \c new
        \li By convention, functions that start with an uppercase letter
            are constructor functions that should only be used with \c new.

    \row
        \li M307
        \li Warning
        \li Use \c new only with functions that start with an uppercase letter
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M308
        \li Warning
        \li Do not use \c Number as a constructor
        \li See also: \l{http://linterrors.com/js/do-not-use-a-as-a-constructor}
            {Do not use {a} as a constructor}.

    \row
        \li M309
        \li Hint
        \li Use spaces around binary operators
        \li

    \row
        \li M310
        \li Warning
        \li Unintentional empty block, use ({}) for empty object literal
        \li

    \row
        \li M311
        \li Hint
        \li Use \c type instead of \c var or \c variant to improve performance
        \li

    \row
        \li M312
        \li Error
        \li Missing property \c number
        \li

    \row
        \li M313
        \li Error
        \li Object value expected
        \li

    \row
        \li M314
        \li Error
        \li Array value expected
        \li

    \row
        \li M315
        \li Error
        \li \c Value value expected
        \li

    \row
        \li M316
        \li Error
        \li Maximum number value is \c number
        \li

    \row
        \li M317
        \li Error
        \li Minimum number value is \c number
        \li

    \row
        \li M318
        \li Error
        \li Maximum number value is exclusive
        \li

    \row
        \li M319
        \li Error
        \li Minimum number value is exclusive
        \li

    \row
        \li M320
        \li Error
        \li String value does not match required pattern
        \li

    \row
        \li M321
        \li Error
        \li Minimum string value length is \c number
        \li

    \row
        \li M322
        \li Error
        \li Maximum string value length is \c number
        \li

    \row
        \li M323
        \li Error
        \li \c Number elements expected in array value
        \li See also:
            \l{http://linterrors.com/js/the-array-literal-notation-is-preferrable}
            {The array literal notation [] is preferable}.

    \row
        \li M324
        \li Error
        \li Hit maximum recursion limit visiting AST, the code model will be unreliable
            and most likely invalid
        \li

    \row
        \li M325
        \li Warning
        \li Logical value does not depend on actual values
        \li

    \row
        \li M326
        \li Error
        \li Components are only allowed to have a single child element
        \li For more information, see \l [QML] {Component}.

    \row
        \li M327
        \li Warning
        \li Components require a child element
        \li For more information, see \l [QML] {Component}.

    \row
        \li M400
        \li Warning
        \li Duplicate import
        \li An import statement has been added twice. For more information,
            see \l{Import Statements}.

    \row
        \li M401
        \li Error
        \li Do not reference the root item as alias
        \li The alias property cannot reference the root component directly.
            Create an instance of the component instead.

    \row
        \li M402
        \li Warning
        \li Avoid referencing the root item in a hierarchy
        \li The alias property cannot reference the root component in a
            hierarchy. Create an instance of the component instead.

    \endtable

    \section1 Resetting the Code Model

    If you change the build and run kit when you have QML files open in the code
    editor, the code model might become corrupt. The following error message
    indicates that this might have happened: \e{Using Qt Quick 1 code model
    instead of Qt Quick 2}.

    You can see the error message when you move the mouse pointer over code that
    \QC underlines in the code editor or when you open a QML file in \QDS.

    To reset the code model, select \uicontrol Tools > \uicontrol {QML/JS} >
    \uicontrol {Reset Code Model}.

    \if defined(qtcreator)
    If this does not help, try changing the QML emulation layer to the one that
    was built with the same Qt version as the one selected in the build and run
    kit.
    \endif

    \section1 Inspecting QML and JavaScript

    To inspect QML and JavaScript properties, methods, and enums, move the
    cursor over them and select \uicontrol Tools > \uicontrol {QML/JS} >
    \uicontrol {Inspect API for Element Under Cursor}.

    \section1 Automatically Formatting QML/JS Files

    To automatically format QML/JS files upon saving, select \uicontrol Edit >
    \uicontrol Preferences > \uicontrol {Qt Quick} > \uicontrol {QML/JS Editing} >
    \uicontrol {Enable auto format on file save}.

    \image qtcreator-qml-js-editing.png "QML/JS Editing preferences"

    \if defined(qtcreator)
    \section1 Inspecting Preprocessed C++ Code

    To analyze the causes of compile errors or errors caused by wrong includes
    pulled in by dependencies or C++ macros expanding to something unexpected,
    select \uicontrol {Show Preprocessed Source} in the editor context menu.

    This action expands all C++ macros to their actual code and removes code that
    is guarded by a currently inactive \c {#ifdef} statements. If you deselect
    the \uicontrol {Use built-in preprocessor to show pre-processed files} check
    box in \uicontrol Edit > \uicontrol Preferences > \uicontrol C++ >
    \uicontrol {Code Model}, this action also expands all
    \c {"#include <foo.h>"} statements to their actual contents.

    \image qtcreator-clang-code-model-options.png "C++ Code Model preferences"

    \endif

*/