`codeSignatures` calculation misses changes in `lazy val` bodies and libraries

[hoangmaihuy]

Please clone https://github.com/hoangmaihuy/mill-caliban-test to reproduce this issue.

Issue 1

Step to reproduce:

1. Run mill selective.prepare __.testCached
2. Go to build.mill and change zioVersion to 2.0.16
3. Run mill selective.resolve __.testCached

Expected: Should output jvm.test.testCached
Actual: No task outputed

Observations

Changing lazy val zioVersion to val ... or def ... resolve this issue

Issue 2

Step to reproduce:

1. Run mill selective.prepare __.testCached
2. Go to build.mill and change mill-caliban version to 0.3.0-RC2
3. Run mill selective.resolve __.testCached

Expected: Should output jvm.test.testCached
Actual: No task outputed

[lihaoyi]

A more minimized repro of the first issue is

import mill.*

lazy val foo = "2.0.16"

def bar = Task{ foo }

lihaoyi mill-caliban-test$ ./mill selective.prepare bar
lihaoyi mill-caliban-test$ vim build.mill 
lihaoyi mill-caliban-test$ ./mill selective.resolve bar

Moving the code change out of lazy val foo into an upstream method also seems to resolve the problem

import mill.*

def qux = "2.0.16"
lazy val foo = qux

def bar = Task{ foo }

Seems like we must incorrectly skipping the lazy val implementation bytecode when computing its code signature

[lihaoyi]

So the problem is that we currently skip computing instruction signatures for lzyINIT methods, since those have an unstable set of instructions based on method ordering. But those methods may also include relevant implementation details, such as the "2.0.16" constant above. So we need to make our code signature computation smarter to allow it to correctly identify changes in the useful code (the 30: ldc #144 // String 2.0.15 below) while ignoreing the unstable parts surrounding it

private java.lang.Object foo$lzyINIT1();
    Code:
       0: aload_0
       1: getfield      #124                // Field foo$lzy1:Ljava/lang/Object;
       4: astore_1
       5: aload_1
       6: ifnonnull     149
       9: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
      12: aload_0
      13: getstatic     #114                // Field OFFSET$0:J
      16: aconst_null
      17: getstatic     #138                // Field scala/runtime/LazyVals$Evaluating$.MODULE$:Lscala/runtime/LazyVals$Evaluating$;
      20: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
      23: ifeq          146
      26: aconst_null
      27: astore_2
      28: aconst_null
      29: astore_3
      30: ldc           #144                // String 2.0.15
      32: astore_3
      33: aload_3
      34: ifnonnull     44
      37: getstatic     #129                // Field scala/runtime/LazyVals$NullValue$.MODULE$:Lscala/runtime/LazyVals$NullValue$;
      40: astore_2
      41: goto          46
      44: aload_3
      45: astore_2
      46: goto          99
      49: astore        4
      51: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
      54: aload_0
      55: getstatic     #114                // Field OFFSET$0:J
      58: getstatic     #138                // Field scala/runtime/LazyVals$Evaluating$.MODULE$:Lscala/runtime/LazyVals$Evaluating$;
      61: aload_2
      62: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
      65: ifne          96
      68: aload_0
      69: getfield      #124                // Field foo$lzy1:Ljava/lang/Object;
      72: checkcast     #41                 // class scala/runtime/LazyVals$Waiting
      75: astore        5
      77: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
      80: aload_0
      81: getstatic     #114                // Field OFFSET$0:J
      84: aload         5
      86: aload_2
      87: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
      90: pop
      91: aload         5
      93: invokevirtual #147                // Method scala/runtime/LazyVals$Waiting.countDown:()V
      96: aload         4
      98: athrow
      99: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
     102: aload_0
     103: getstatic     #114                // Field OFFSET$0:J
     106: getstatic     #138                // Field scala/runtime/LazyVals$Evaluating$.MODULE$:Lscala/runtime/LazyVals$Evaluating$;
     109: aload_2
     110: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
     113: ifne          144
     116: aload_0
     117: getfield      #124                // Field foo$lzy1:Ljava/lang/Object;
     120: checkcast     #41                 // class scala/runtime/LazyVals$Waiting
     123: astore        5
     125: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
     128: aload_0
     129: getstatic     #114                // Field OFFSET$0:J
     132: aload         5
     134: aload_2
     135: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
     138: pop
     139: aload         5
     141: invokevirtual #147                // Method scala/runtime/LazyVals$Waiting.countDown:()V
     144: aload_3
     145: areturn
     146: goto          0
     149: aload_1
     150: instanceof    #35                 // class scala/runtime/LazyVals$LazyValControlState
     153: ifeq          204
     156: aload_1
     157: getstatic     #138                // Field scala/runtime/LazyVals$Evaluating$.MODULE$:Lscala/runtime/LazyVals$Evaluating$;
     160: if_acmpne     185
     163: getstatic     #101                // Field scala/runtime/LazyVals$.MODULE$:Lscala/runtime/LazyVals$;
     166: aload_0
     167: getstatic     #114                // Field OFFSET$0:J
     170: aload_1
     171: new           #41                 // class scala/runtime/LazyVals$Waiting
     174: dup
     175: invokespecial #149                // Method scala/runtime/LazyVals$Waiting."<init>":()V
     178: invokevirtual #142                // Method scala/runtime/LazyVals$.objCAS:(Ljava/lang/Object;JLjava/lang/Object;Ljava/lang/Object;)Z
     181: pop
     182: goto          0
     185: aload_1
     186: instanceof    #41                 // class scala/runtime/LazyVals$Waiting
     189: ifeq          202
     192: aload_1
     193: checkcast     #41                 // class scala/runtime/LazyVals$Waiting
     196: invokevirtual #152                // Method scala/runtime/LazyVals$Waiting.await:()V
     199: goto          0
     202: aconst_null
     203: areturn
     204: aload_1
     205: areturn