Eric Milles created GROOVY-8742:
-----------------------------------
Summary: Line number information for method is confusing debugger
Key: GROOVY-8742
URL:
Project: Groovy
Issue Type: Bug
Components: bytecode, class generator
Affects Versions: 2.4.15
Reporter: Eric Milles
I have been investigating a case where the IDE will not break on a line breakpoint in a test
method. This method has no parameters or local variables (this affects its line number table
in the bytecode) and the code is all on one line. When line-breaking the code or assigning
to temporary, the line numbers table changes and the line breakpoints work as expected.
{code:groovy}
package a
import org.junit.*
final class Tests {
@Test
void testSomething() { // line 29
assertSomething(instance.method(one, "two", Three.class)) // line 30
}
}
{code}
When compiled with Groovy 2.4 and normal/dynamic groovy, the method has line information:
{code}
Line numbers:
[pc: 4, line: 29]
[pc: 19, line: 30]
[pc: 68, line: 30]
Local variable table:
[pc: 0, pc: 109] local: this index: 0 type: a.Tests
{code}
I have not tried with the "fast path" optimization disabled. I think its prelude is what
bumps the PC from 0 to 4 and results in the two PC entries for line 30 (pc 19 and pc 68).
If I assign the result of {{method}} to a new local variable, the line numbers are altered:
{code}
Line numbers:
[pc: 6, line: 30]
[pc: 63, line: 30]
[pc: 100, line: 31]
Local variable table:
[pc: 0, pc: 113] local: this index: 0 type: a.Tests
[pc: 6, pc: 113] local: variable index: 2 type: java.lang.Object
{code}
If I compile with invoke dynamic on, I get this for the original code:
{code}
Line numbers:
[pc: 0, line: 30]
Local variable table:
[pc: 0, pc: 30] local: this index: 0 type: a.Tests
{code}
I'm not sure the exact outcome expected here in terms of the bytecode, but I looked at similar
methods from Java sources. For a Java test method, the line number table began with {{[pc:
0, line: whatever]}}.
I looked at GROOVY-4505, which mentions that {{AsmClassGenerator.visitBlockStatement}} should
not be writing line number information for the block statement (the source of line 29). {{StatementWriter.writeBlockStatement}}
indeed retains a note about this. However, the overload in {{OptimizingStatementWriter}}
still triggers `onLineNumber` from its `writeBlockStatement` -> {{writeGuards}}. Should
{{onLineNumber}} check for {{BlockStatement}} and exit early? I tried this quickly and it
did alter the line numbers table, but it did not help my debugger find the breakpoint on line
30.
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