Skip to content

Commit f8d80ea

Browse files
retronymretronym
committed
SI-3452 Correct Java generic signatures for mixins, static forwarders
[Parts of this patch and some of the commentary are from @paulp] This took me so long to figure out I can't even tell you. Partly because there were two different bugs, one which only arose for trait forwarders and one for mirror class forwarders, and every time I'd make one set of tests work another set would start failing. The runtime failures associated with these bugs were fairly well hidden because you usually have to go through java to encounter them: scala doesn't pay that much attention to generic signatures, so they can be wrong and scala might still generate correct code. But java is not so lucky. Bug #1) During mixin composition, classes which extend traits receive forwarders to the implementations. An attempt was made to give these the correct info (in method "cloneBeforeErasure") but it was prone to giving the wrong answer, because: the key attribute which the forwarder must capture is what the underlying method will erase to *where the implementation is*, not how it appears to the class which contains it. That means the signature of the forwarder must be no more precise than the signature of the inherited implementation unless additional measures will be taken. This subtle difference will put on an unsubtle show for you in test run/t3452.scala. trait C[T] trait Search[M] { def search(input: M): C[Int] = null } object StringSearch extends Search[String] { } StringSearch.search("test"); // java // java.lang.NoSuchMethodError: StringSearch.search(Ljava/lang/String;)LC; The principled thing to do here would be to create a pair of methods in the host class: a mixin forwarder with the erased signature `(String)C[Int]`, and a bridge method with the same erased signature as the trait interface facet. But, this turns out to be pretty hard to retrofit onto the current setup of Mixin and Erasure, mostly due to the fact that mixin happens after erasure which has already taken care of bridging. For a future, release, we should try to move all bridging after mixin, and pursue this approach. But for now, what can we do about `LinkageError`s for Java clients? This commit simply checks if the pre-erasure method signature that we generate for the trait forward erases identically to that of the interface method. If so, we can be precise. If not, we emit the erased signature as the generic signature. Bug #2) The same principle is at work, at a different location. During genjvm, objects without declared companion classes are given static forwarders in the corresponding class, e.g. object Foo { def bar = 5 } which creates these classes (taking minor liberties): class Foo$ { static val MODULE$ = new Foo$ ; def bar = 5 } class Foo { static def bar = Foo$.MODULE$.bar } In generating these, genjvm circumvented the usual process whereby one creates a symbol and gives it an info, preferring to target the bytecode directly. However generic signatures are calculated from symbol info (in this case reusing the info from the module class.) Lacking even the attempt which was being made in mixin to "clone before erasure", we would have runtime failures of this kind: abstract class Foo { type T def f(x: T): List[T] = List() } object Bar extends Foo { type T = String } Bar.f(""); // java // java.lang.NoSuchMethodError: Bar.f(Ljava/lang/String;)Lscala/collection/immutable/List; Before/after this commit: < signature f (Ljava/lang/String;)Lscala/collection/immutable/List<Ljava/lang/String;>; --- > signature f (Ljava/lang/Object;)Lscala/collection/immutable/List<Ljava/lang/Object;>; This takes the warning count for compiling collections under `-Ycheck:jvm` from 1521 to 26.
1 parent 3306967 commit f8d80ea

31 files changed

+649
-13
lines changed

‎src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1064,7 +1064,18 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
10641064
)
10651065

10661066
// TODO needed? for(ann <- m.annotations) { ann.symbol.initialize }
1067-
val jgensig = if (m.isDeferred) null else getGenericSignature(m, module); // only add generic signature if method concrete; bug #1745
1067+
val jgensig = (
1068+
// only add generic signature if method concrete; bug #1745
1069+
if (m.isDeferred) null else {
1070+
val clazz = module.linkedClassOfClass
1071+
val m1 = (
1072+
if ((clazz.info member m.name) eq NoSymbol)
1073+
enteringErasure(m.cloneSymbol(clazz, Flags.METHOD | Flags.STATIC))
1074+
else m
1075+
)
1076+
getGenericSignature(m1, clazz)
1077+
}
1078+
)
10681079
addRemoteExceptionAnnot(isRemoteClass, hasPublicBitSet(flags), m)
10691080
val (throws, others) = m.annotations partition (_.symbol == ThrowsClass)
10701081
val thrownExceptions: List[String] = getExceptions(throws)

‎src/compiler/scala/tools/nsc/transform/Mixin.scala

Lines changed: 16 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -172,18 +172,23 @@ abstract class Mixin extends InfoTransform with ast.TreeDSL {
172172
// info) as they are seen from the class. We can't use the member that we get from the
173173
// implementation class, as it's a clone that was made after erasure, and thus it does not
174174
// know its info at the beginning of erasure anymore.
175-
// Optimize: no need if mixinClass has no typeparams.
176-
mixinMember cloneSymbol clazz modifyInfo (info =>
177-
if (mixinClass.typeParams.isEmpty) info
178-
else (clazz.thisType baseType mixinClass) memberInfo mixinMember
179-
)
175+
val sym = mixinMember cloneSymbol clazz
176+
177+
val erasureMap = erasure.erasure(mixinMember)
178+
val erasedInterfaceInfo: Type = erasureMap(mixinMember.info)
179+
val specificForwardInfo = (clazz.thisType baseType mixinClass) memberInfo mixinMember
180+
val forwarderInfo =
181+
if (erasureMap(specificForwardInfo) =:= erasedInterfaceInfo)
182+
specificForwardInfo
183+
else {
184+
erasedInterfaceInfo
185+
}
186+
// Optimize: no need if mixinClass has no typeparams.
187+
// !!! JZ Really? What about the effect of abstract types, prefix?
188+
if (mixinClass.typeParams.isEmpty) sym
189+
else sym modifyInfo (_ => forwarderInfo)
180190
}
181-
// clone before erasure got rid of type info we'll need to generate a javaSig
182-
// now we'll have the type info at (the beginning of) erasure in our history,
183-
// and now newSym has the info that's been transformed to fit this period
184-
// (no need for asSeenFrom as phase.erasedTypes)
185-
// TODO: verify we need the updateInfo and document why
186-
newSym updateInfo (mixinMember.info cloneInfo newSym)
191+
newSym
187192
}
188193

189194
/** Add getters and setters for all non-module fields of an implementation

‎test/files/neg/t4749.check

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -25,6 +25,10 @@ t4749.scala:26: warning: Fail6 has a main method with parameter type Array[Strin
2525

2626
object Fail6 {
2727
^
28+
t4749.scala:42: warning: Win3 has a main method with parameter type Array[String], but bippy.Win3 will not be a runnable program.
29+
Reason: main method must have exact signature (Array[String])Unit
30+
object Win3 extends WinBippy[Unit] { }
31+
^
2832
error: No warnings can be incurred under -Xfatal-warnings.
29-
6 warnings found
33+
7 warnings found
3034
one error found

‎test/files/pos/t3452f.scala

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,10 @@
1+
class Base[Coll] {
2+
trait Transformed[S] {
3+
lazy val underlying: Coll = ???
4+
}
5+
}
6+
7+
class Derived extends Base[String] {
8+
class C extends Transformed[Any]
9+
}
10+

‎test/files/run/mixin-signatures.check

Lines changed: 59 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,59 @@
1+
class Test$bar1$ {
2+
public java.lang.String Test$bar1$.f(java.lang.Object)
3+
public java.lang.Object Test$bar1$.f(java.lang.Object) <bridge> <synthetic>
4+
public java.lang.String Test$bar1$.g(java.lang.String)
5+
public java.lang.Object Test$bar1$.g(java.lang.Object) <bridge> <synthetic>
6+
public java.lang.String Test$bar1$.g(java.lang.Object) <bridge> <synthetic>
7+
public java.lang.Object Test$bar1$.h(java.lang.Object)
8+
}
9+
10+
class Test$bar2$ {
11+
public java.lang.Object Test$bar2$.f(java.lang.String)
12+
public java.lang.Object Test$bar2$.f(java.lang.Object) <bridge> <synthetic>
13+
public java.lang.String Test$bar2$.g(java.lang.String)
14+
public java.lang.Object Test$bar2$.g(java.lang.Object) <bridge> <synthetic>
15+
public java.lang.Object Test$bar2$.g(java.lang.String) <bridge> <synthetic>
16+
public java.lang.Object Test$bar2$.h(java.lang.Object)
17+
}
18+
19+
class Test$bar3$ {
20+
public java.lang.String Foo3.f(java.lang.Object)
21+
generic: public java.lang.String Foo3.f(T)
22+
public java.lang.Object Foo3.f(java.lang.Object) <bridge> <synthetic>
23+
public java.lang.String Test$bar3$.g(java.lang.String)
24+
public java.lang.Object Test$bar3$.g(java.lang.Object) <bridge> <synthetic>
25+
public java.lang.String Test$bar3$.g(java.lang.Object) <bridge> <synthetic>
26+
public java.lang.Object Foo3.h(java.lang.Object)
27+
}
28+
29+
class Test$bar4$ {
30+
public java.lang.Object Foo4.f(java.lang.String)
31+
generic: public R Foo4.f(java.lang.String)
32+
public java.lang.Object Foo4.f(java.lang.Object) <bridge> <synthetic>
33+
public java.lang.String Test$bar4$.g(java.lang.String)
34+
public java.lang.Object Test$bar4$.g(java.lang.Object) <bridge> <synthetic>
35+
public java.lang.Object Test$bar4$.g(java.lang.String) <bridge> <synthetic>
36+
public java.lang.Object Foo4.h(java.lang.Object)
37+
}
38+
39+
class Test$bar5$ {
40+
public java.lang.String Test$bar5$.f(java.lang.String)
41+
public java.lang.Object Test$bar5$.f(java.lang.Object) <bridge> <synthetic>
42+
public java.lang.Object Test$bar5$.f(java.lang.String) <bridge> <synthetic>
43+
public java.lang.String Test$bar5$.f(java.lang.Object) <bridge> <synthetic>
44+
public java.lang.String Test$bar5$.g(java.lang.String)
45+
public java.lang.Object Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
46+
public java.lang.Object Test$bar5$.g(java.lang.String) <bridge> <synthetic>
47+
public java.lang.String Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
48+
public java.lang.Object Test$bar5$.h(java.lang.Object)
49+
}
50+
51+
class Foo1$class {
52+
public static java.lang.String Foo1$class.f(Foo1,java.lang.Object)
53+
}
54+
55+
class Foo2$class {
56+
public static java.lang.Object Foo2$class.f(Foo2,java.lang.String)
57+
}
58+
59+
000000000000000000000000000000000000

‎test/files/run/mixin-signatures.scala

Lines changed: 105 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,105 @@
1+
trait Base[T, R] {
2+
def f(x: T): R
3+
def g(x: T): R
4+
def h(x: T): R = null.asInstanceOf[R]
5+
}
6+
7+
trait Foo1[T] extends Base[T, String] {
8+
def f(x: T): String = null
9+
def g(x: T): String
10+
}
11+
trait Foo2[R] extends Base[String, R] {
12+
def f(x: String): R = { print(x.length) ; null.asInstanceOf[R] }
13+
def g(x: String): R
14+
}
15+
abstract class Foo3[T] extends Base[T, String] {
16+
def f(x: T): String = ""
17+
def g(x: T): String
18+
}
19+
abstract class Foo4[R] extends Base[String, R] {
20+
def f(x: String): R = { print(x.length) ; null.asInstanceOf[R] }
21+
def g(x: String): R
22+
}
23+
24+
object Test {
25+
object bar1 extends Foo1[String] { def g(x: String): String = { print(x.length) ; "" } }
26+
object bar2 extends Foo2[String] { def g(x: String): String = { print(x.length) ; "" } }
27+
object bar3 extends Foo3[String] { def g(x: String): String = { print(x.length) ; "" } }
28+
object bar4 extends Foo4[String] { def g(x: String): String = { print(x.length) ; "" } }
29+
30+
// Notice that in bar5, f and g require THREE bridges, because the final
31+
// implementation is (String)String, but:
32+
//
33+
// inherited abstract signatures: T(R), (T)String, and (String)R
34+
// which erase to: (Object)Object, (Object)String, and (String)Object
35+
//
36+
// each of which must be bridged to the actual (String)String implementation.
37+
//
38+
// public java.lang.String Test$bar5$.g(java.lang.String)
39+
// public java.lang.Object Test$bar5$.g(java.lang.String) <bridge> <synthetic>
40+
// public java.lang.Object Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
41+
// public java.lang.String Test$bar5$.g(java.lang.Object) <bridge> <synthetic>
42+
object bar5 extends Foo1[String] with Foo2[String] {
43+
override def f(x: String): String = { print(x.length) ; x }
44+
def g(x: String): String = { print(x.length) ; x }
45+
}
46+
47+
final def m1[T, R](x: Base[T, R], y: T) = { x.f(y) ; x.g(y) ; x.h(y) }
48+
final def m2[T](x: Base[T, String], y: T) = { x.f(y) ; x.g(y) ; x.h(y) }
49+
final def m3[R](x: Base[String, R]) = { x.f("") ; x.g("") ; x.h("") }
50+
final def m4(x: Base[String, String]) = { x.f("") ; x.g("") ; x.h("") }
51+
52+
final def m11[T](x: Foo1[T], y: T) = { x.f(y) ; x.g(y) ; x.h(y) }
53+
final def m12(x: Foo1[String]) = { x.f("") ; x.g("") ; x.h("") }
54+
final def m21[T](x: Foo2[T], y: T) = { x.f("") ; x.g("") ; x.h("") }
55+
final def m22(x: Foo2[String]) = { x.f("") ; x.g("") ; x.h("") }
56+
final def m31[T](x: Foo3[T], y: T) = { x.f(y) ; x.g(y) ; x.h(y) }
57+
final def m32(x: Foo3[String]) = { x.f("") ; x.g("") ; x.h("") }
58+
final def m41[T](x: Foo4[T], y: T) = { x.f("") ; x.g("") ; x.h("") }
59+
final def m42(x: Foo4[String]) = { x.f("") ; x.g("") ; x.h("") }
60+
61+
def go = {
62+
m1(bar1, "") ; m2(bar1, "") ; m3(bar1) ; m4(bar1)
63+
m1(bar2, "") ; m2(bar2, "") ; m3(bar2) ; m4(bar2)
64+
m1(bar3, "") ; m2(bar3, "") ; m3(bar3) ; m4(bar3)
65+
m1(bar4, "") ; m2(bar4, "") ; m3(bar4) ; m4(bar4)
66+
67+
m11(bar1, "") ; m12(bar1)
68+
m21(bar2, "") ; m22(bar2)
69+
m31(bar3, "") ; m32(bar3)
70+
m41(bar4, "") ; m42(bar4)
71+
""
72+
}
73+
74+
def flagsString(m: java.lang.reflect.Method) = {
75+
val str = List(
76+
if (m.isBridge) "<bridge>" else "",
77+
if (m.isSynthetic) "<synthetic>" else ""
78+
) filterNot (_ == "") mkString " "
79+
80+
if (str == "") "" else " " + str
81+
//
82+
// val flags = scala.reflect.internal.ClassfileConstants.toScalaMethodFlags(m.getModifiers())
83+
// scala.tools.nsc.symtab.Flags.flagsToString(flags)
84+
}
85+
86+
def show(clazz: Class[_]) {
87+
print(clazz + " {")
88+
clazz.getMethods.sortBy(x => (x.getName, x.isBridge, x.toString)) filter (_.getName.length == 1) foreach { m =>
89+
print("\n " + m + flagsString(m))
90+
if ("" + m != "" + m.toGenericString) {
91+
print("\n generic: " + m.toGenericString)
92+
}
93+
}
94+
println("\n}")
95+
println("")
96+
}
97+
def show(x: AnyRef) { show(x.getClass) }
98+
def show(x: String) { show(Class.forName(x)) }
99+
100+
def main(args: Array[String]): Unit = {
101+
List(bar1, bar2, bar3, bar4, bar5) foreach show
102+
List("Foo1$class", "Foo2$class") foreach show
103+
println(go)
104+
}
105+
}

‎test/files/run/t3452.check

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
4

‎test/files/run/t3452.scala

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
trait IStringPair[T] {
2+
def a : String
3+
def b : String
4+
def build(a : String, b : String) : T
5+
def cat(that : IStringPair[T]) = build(this.a + that.a, this.b + that.b)
6+
override def toString = a + b
7+
}
8+
9+
class StringPair(val a : String, val b : String) extends IStringPair[StringPair] {
10+
def build(a : String, b : String) = new StringPair(a, b)
11+
def len = a.length + b.length
12+
}
13+
14+
object Test {
15+
def main(args: Array[String]): Unit = {
16+
val a = new StringPair("A", "B")
17+
val b = new StringPair("1", "2")
18+
val c = a cat b
19+
println(c.len)
20+
}
21+
}

‎test/files/run/t3452a.check

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
BulkSearch.searchFor called.

‎test/files/run/t3452a/J_2.java

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
public class J_2 {
2+
public static void main(String[] args) {
3+
BulkSearchInstance.searchFor(new UpRelation());
4+
}
5+
}

‎test/files/run/t3452a/S_1.scala

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,24 @@
1+
abstract class BulkSearch {
2+
type R <: Row
3+
type Rel <: Relation [R]
4+
type Corr <: Correspondence[R]
5+
6+
def searchFor(input: Rel): Mapping[Corr] = { println("BulkSearch.searchFor called.") ; null }
7+
}
8+
9+
object BulkSearchInstance extends BulkSearch {
10+
type R = UpRow
11+
type Rel = UpRelation
12+
type Corr = UpCorrespondence
13+
}
14+
15+
class Row
16+
class UpRow extends Row
17+
18+
class Relation [R <: Row]
19+
class UpRelation extends Relation [UpRow]
20+
21+
class Correspondence [R <: Row]
22+
class UpCorrespondence extends Correspondence [UpRow]
23+
24+
class Mapping[MC <: Correspondence[_]]

‎test/files/run/t3452a/S_3.scala

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
object Test {
2+
def main(args: Array[String]): Unit = {
3+
J_2.main(args)
4+
}
5+
}

‎test/files/run/t3452b.check

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
Search received: test

‎test/files/run/t3452b/J_2.java

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
public class J_2 {
2+
public static void j() {
3+
StringSearch.search("test");
4+
}
5+
}

‎test/files/run/t3452b/S_1.scala

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,10 @@
1+
trait Search[M] {
2+
def search(input: M): C[Int] = {
3+
println("Search received: " + input)
4+
null
5+
}
6+
}
7+
8+
object StringSearch extends Search[String]
9+
10+
trait C[T]

‎test/files/run/t3452b/S_3.scala

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
object Test {
2+
def main(args: Array[String]): Unit = {
3+
J_2.j()
4+
}
5+
}

‎test/files/run/t3452c.check

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
3
2+
3
3+
3
4+
3
5+
3
6+
3
7+
3
8+
3

0 commit comments

Comments
 (0)