Monday 12 March 2018

How ABAP syntax highlight is implemented in “WebIDE” launched via browser

I have introduced the step how to launch tcode SE80 by Fiori launchpad and run it in the browser with the help of SAP ITS.

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It’s cool but not that cool because the syntax highlight is missing in ABAP editor opened there.

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The syntax highlight is supported there:

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Then a question comes to my mind: how does the browser know which token(such as ABAP keyword) should be highlighted and which token not(such as normal variable). Again I managed to debug myself to find the answer.

How to debug by yourself to find the answer


1. type a keyword for example data, and it is highlighed with purple color.
The color is implemented by css class ace_keyword.

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Search “.ace_keyword” via Chrome development tool and find it is hard coded in theme-sap-cumulus.js, instead of declared in any dedicated css file.

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When the application is launched, the hard coded string contains lots of syntax color related css class is dynamically appended to document node by creating a new style node as demonstrated below.

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2. Type “.xml” as filter in Chrome network tab, and the implementation for ABAP editor in the browser could be found: it is declared in Editor.view.xml, which acts as a container.

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Scroll to the top of Editor.view.xml in order to figure out the value of reuse namespace: sap.nw.core.ext.lib.reuse.controls

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then you can find the UI5 application which implements the ABAP editor: nw_aps_ext_lib.

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You can find the complete implementation of this application in SAPGUI: it’s really worth study if you are a frontend fan:

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Open the file ABAPWrapper-dbg.js under the controls folder and set a breakpoint in line 68. This function call is responsible to fetch an important PAD file which is relevant for syntax highlight from backend server.

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Refresh the application, breakpoint is triggered, you can save the response from backend server locally and open it via a text editor:

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This is the header of PAD file which contains a list of ALL ABAP keywords and other language elements which are related to syntax highlight. This PAD file works as a kind of dictionary which guides the UI5 application to highlight each token in the source code with corresponding css class.

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3. the last step is when, where and how a given css class is assigned.

Suppose I want to type a “w” character here and according to previous analysis, a css class “ace_keyword” will be assigned.

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as soon as I typed “w”, breakpoint is triggered, the current line in the editor, line 8( index starts from 0) is determined.

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$renderLine is responsible to populate corresponding HTML source code. The string “new” is passed into getLineTokens to calculate its language type: keyword or variable?

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In AceRndTokenizer.js, the ABAP parser successfully judges “new” as a keyword, as it holds the content of PAD file loaded from backend server.

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4. The corresponding css class name ace_keyword is combined here and appended to a StringBuilder:

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finally the innerHTML attribute of DOM element for “new” token in ABAP editor is filled by the value containing css class ace_keyword:

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