RFR: 8339068: [Linux] NPE: Cannot read field "firstFont" because "<local4>" is null

[John Hendrikx]

On Tue, 27 Aug 2024 15:50:54 GMT, Jose Pereda <jpereda at openjdk.org> wrote:

> This PR adds a couple of null checks to `LogicalFont` and `FTFactory`, that make use of `FontConfigManager::getFontConfigFont`, which under certain cases, can return null.
> 
> I've tested this PR on both Linux (Ubuntu 22.04.4) and Android, just using `-Dprism.useFontConfig=false`.
> 
> On Ubuntu, I've manually added some font files to the JDK path `$JAVA_HOME/lib/fonts` (which didn't exist), and the test passes now, though this message is still printed out:
> 
> Error: JavaFX detected no fonts! Please refer to release notes for proper font configuration
> 
> which is confusing to me, because fonts where found in the JDK path after all, and even in the case that there were no fonts found, "the release notes" is an ambiguous reference for the user. 
> 
> Also, instead of adding fonts to the JDK, I tested adding a `logicalfonts.properties` file with `-Dprism.fontdir` and without `fontConfig`, but this case was already working before the patch for this PR, and still works after it.
> 
> Note that if there are no fonts in the JDK path, and `prism.fontdir` is not provided, without `fontConfig`, after this PR, there will still be an exception:
> 
> 
> Caused by: java.lang.NullPointerException: Cannot invoke "com.sun.javafx.font.FontResource.getDefaultAAMode()" because the return value of "com.sun.javafx.font.LogicalFont.getSlot0Resource()" is null
>         at javafx.graphics at 24-internal/com.sun.javafx.font.LogicalFont.getDefaultAAMode(LogicalFont.java:456)
>         at javafx.graphics at 24-internal/com.sun.javafx.font.LogicalFont.getStrike(LogicalFont.java:461)
>         at javafx.graphics at 24-internal/com.sun.javafx.font.PrismFont.getStrike(PrismFont.java:79)
>         at javafx.graphics at 24-internal/com.sun.javafx.text.PrismTextLayout.setContent(PrismTextLayout.java:139)
>         at javafx.graphics at 24-internal/javafx.scene.text.Text.getTextLayout(Text.java:303)
>         at javafx.graphics at 24-internal/javafx.scene.text.Text.needsFullTextLayout(Text.java:258)
>         at javafx.graphics at 24-internal/javafx.scene.text.Text$6.invalidated(Text.java:576)
>  ...
> 
> 
> because `LogicalFont::getSlot0Resource` will return null. Adding null checks after this point will require many changes (`LogicalFont::getSlotResource(0)` is used in many places). Shouldn't we fail gracefully after `LogicalFont::getSlot0Resource` if `slot0FontResource` is finally null?

The changes seem to deal with the case where Font Config is unavailable on Linux.  I think those changes are fine.  However, if it turns out there isn't any font at all (via an alternative source) I think it would be best to just fail.

modules/javafx.graphics/src/main/java/com/sun/javafx/font/LogicalFont.java line 180:

> 178:                 physicalFullName = fcCompFont.firstFont.fullName;
> 179:                 physicalFileName = fcCompFont.firstFont.fontFile;
> 180:             }

These changes seem okay, as it is assuming that the font is available via font config, but it may have originated from somewhere else.

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PR Comment: https://git.openjdk.org/jfx/pull/1546#issuecomment-2313223687
PR Review Comment: https://git.openjdk.org/jfx/pull/1546#discussion_r1733329665