On Wed, 26 May 2021 17:52:36 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
>> This is a preview of a patch implementing JEP 406: Pattern Matching for >> switch (Preview): >> https://bugs.openjdk.java.net/browse/JDK-8213076 >> >> The current draft of the specification is here: >> http://cr.openjdk.java.net/~gbierman/jep406/jep406-20210430/specs/patterns-switch-jls.html >> >> A summary of notable parts of the patch: >> -to support cases expressions and patterns in cases, there is a new common >> superinterface for expressions and patterns, `CaseLabelTree`, which >> expressions and patterns implement, and a list of case labels is returned >> from `CaseTree.getLabels()`. >> -to support `case default`, there is an implementation of `CaseLabelTree` >> that represents it (`DefaultCaseLabelTree`). It is used also to represent >> the conventional `default` internally and in the newly added methods. >> -in the parser, parenthesized patterns and expressions need to be >> disambiguated when parsing case labels. >> -Lower has been enhanced to handle `case null` for ordinary >> (boxed-primitive, String, enum) switches. This is a bit tricky for boxed >> primitives, as there is no value that is not part of the input domain so >> that could be used to represent `case null`. Requires a bit shuffling with >> values. >> -TransPatterns has been enhanced to handle the pattern matching switch. It >> produces code that delegates to a new bootstrap method, that will classify >> the input value to the switch and return the case number, to which the >> switch then jumps. To support guards, the switches (and the bootstrap >> method) are restartable. The bootstrap method as such is written very simply >> so far, but could be much more optimized later. >> -nullable type patterns are `case String s, null`/`case null, String >> s`/`case null: case String s:`/`case String s: case null:`, handling of >> these required a few tricks in `Attr`, `Flow` and `TransPatterns`. >> >> The specdiff for the change is here (to be updated): >> http://cr.openjdk.java.net/~jlahoda/8265981/specdiff.preview.01/overview-summary.html > > Jan Lahoda has updated the pull request with a new target base due to a merge > or a rebase. The pull request now contains 12 commits: > > - Post-merge fix - need to include jdk.internal.javac in the list of > packages used by jdk.compiler again, as we now (again) have a preview feature > in javac. > - Correcting LineNumberTable for rule switches. > - Merging master into JDK-8262891 > - Fixing various error-related bugs. > - Avoiding fall-through from the total case to a synthetic default but > changing total patterns to default. > - Reflecting recent spec changes. > - Reflecting review comments. > - Reflecting review comments on SwitchBootstraps. > - Trailing whitespaces. > - Cleanup, reflecting review comments. > - ... and 2 more: > https://git.openjdk.java.net/jdk/compare/083416d3...fd748501 > I've updated the code to produce better/more useful LineNumberTable for rule > switches. @lahodaj I re-tested previous example and tested few others. Now everything seems to be good with `LineNumberTable` entries 👍 ---- However I also noticed that for class Example { void example(String s) { switch (s) { case "a": System.out.println("a"); } } } there is difference in frames before and after this PR javap -v -p Example.class diff is line 3: 0 line 5: 60 line 7: 68 - StackMapTable: number_of_entries = 4 + StackMapTable: number_of_entries = 5 frame_type = 253 /* append */ - offset_delta = 28 + offset_delta = 4 locals = [ class java/lang/String, int ] + frame_type = 23 /* same */ frame_type = 10 /* same */ frame_type = 20 /* same */ frame_type = 249 /* chop */ and java -cp asm-util-9.1.jar:asm-9.1.jar org.objectweb.asm.util.Textifier Example.class diff is + L1 + FRAME APPEND [java/lang/String I] ALOAD 2 INVOKEVIRTUAL java/lang/String.hashCode ()I LOOKUPSWITCH - 97: L1 - default: L2 - L1 - FRAME APPEND [java/lang/String I] + 97: L2 + default: L3 + L2 + FRAME SAME Don't know about importance of this, and whether this was expected, but decided to mention. ------------- Marked as reviewed by godin (Author). PR: https://git.openjdk.java.net/jdk/pull/3863
