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Use method entry line number for synthetic code in suspend fun.

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If no line number is emitted, the line number of the last line
in the suspend function is used. That combined with the IntelliJ
debuggers handling of breakpoint setting and the D8 dexers
reordering of blocks can lead to cases where breakpoints on
the last line of a suspend function are never hit.

See https://youtrack.jetbrains.com/issue/KT-51936 for details.

^Fixed KT-51936
This commit is contained in:
Mads Ager
2022-04-11 13:00:15 +02:00
committed by teamcity
parent a07e21d913
commit bfe8c3b263
1 changed files with 32 additions and 0 deletions
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compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/CoroutineTransformerMethodVisitor.kt
+32
View File
@@ -160,7 +160,39 @@ class CoroutineTransformerMethodVisitor(
insert(firstStateLabel, withInstructionAdapter {
generateResumeWithExceptionCheck(dataIndex)
})
// Insert throw of an IllegalStateException if the resumption point is unknown. This code does not correspond to
// anything in the input code. We give it the entry line number instead of letting it inherit the line number
// of the last branch to avoid debugger issues where reordering the blocks leads to inability to set a breakpoint
// on the last expression in a suspend function. See KT-51936 for a concrete example.
//
// The IntelliJ debugger tries to avoid stuttering by only setting a breakpoint on the first bytecode offset that
// corresponds to a line number. Therefore, if the code is generated as:
//
// line 1: switch
// line 2: case 1: ...
// line 3: ...
// line 4: case 2: ...
// line 5: ...
// default: throw IllegalStateException
//
// The default case ends up with line number 5. Now, compilers could (and the D8 dexer someties does) reorder
// the blocks for the cases to end up with:
//
// line 1: switch
// line 5: default : throw IllegalStateException
// line 2: case 1: ...
// line 3: ...
// line 4: case 2: ...
// line 5: ...
//
// This is equivalent to the original code. However, if the user tries to set a breakpoint on line 5, it will
// ONLY be set on the throw of the IllegalStateException and not in the actual user code in case 2. And therefore
// it is impossible for a developer to hit a breakpoint on the last line of a suspend function.
//
// Using line 1 for the default case limits this issue as the entry block is rarely (if ever) reordered.
insert(last, defaultLabel)
insert(last, LineNumberNode(lineNumber, defaultLabel))
insert(last, withInstructionAdapter {
AsmUtil.genThrow(this, "java/lang/IllegalStateException", ILLEGAL_STATE_ERROR_MESSAGE)