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Fix: Optional pre-type won't cause a crash anymore #5442

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merged 9 commits into from
May 17, 2024
Merged

Fix: Optional pre-type won't cause a crash anymore #5442

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5906960
Add test for issue #5369
MikaelMayer May 14, 2024
a44d8b1
Fix: Optional pre-type won't cause a crash anymore
MikaelMayer May 14, 2024
79dfa4c
Merge branch 'master' into fix-5369-crash-new-resolver
MikaelMayer May 15, 2024
87aa2c5
Merge branch 'master' into fix-5369-crash-new-resolver
MikaelMayer May 15, 2024
eb0327c
Merge branch 'master' into fix-5369-crash-new-resolver
MikaelMayer May 16, 2024
cfa8acb
Added comment
MikaelMayer May 16, 2024
12310a8
Review comments
MikaelMayer May 16, 2024
0faf793
Update fix and expect file
keyboardDrummer May 17, 2024
4445b96
Merge branch 'master' into fix-5369-crash-new-resolver
MikaelMayer May 17, 2024
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3 changes: 3 additions & 0 deletions Source/DafnyCore/Resolver/PreType/PreType.cs
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Expand Up @@ -455,6 +455,9 @@ public class PreTypePlaceholderModule : PreTypePlaceholder {
public class PreTypePlaceholderType : PreTypePlaceholder {
}

/// Currently used exclusively for assigning a pre-type to MemberSelect expressions, such as "obj.method",
/// which is not considered an expression. This indicates that resolution has occurred,
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What do you mean by MemberSelect not being considered an expression? It inherits from Expression

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It weirdly is an Expression, but not a true Dafny expression: you cannot use it in a regular Dafny expression. Consider the following:

class A {
  method Test() {
  }
}
method Main() {
  var a := new A();
  var f := a.Test; // Error, expected a Dafny expression on the RHS
  f();
}

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It is also used for fields, in which case it is an expression, right?

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@keyboardDrummer keyboardDrummer May 16, 2024 •
edited
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It seems nice to conceptually consider a MemberSelectExpr that references a method still an expression, even if we don't allow it in an expression context. If we do that, then I would expect to assign some sort of callable type to it. Could we rename UnusedPreType to Method[Pre]Type?

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Yes, it's used for fields and in that case it's indeed an expression.

I did the renaming, hoping it won't break any future development.

/// even though the pre-type itself is not useful.
public class UnusedPreType : PreTypePlaceholder {
public readonly string Why;

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2 changes: 2 additions & 0 deletions Source/DafnyCore/Resolver/PreType/PreTypeConstraints.cs
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Expand Up @@ -583,6 +583,8 @@ public enum CommonConfirmationBag {
preType = preType.Normalize();
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Can you add a comment to ConfirmConstraint, or update its signature (parameter names) to make it clear what it does? I don't understand the meaning of the parameters or return value by looking at just its signature and comment.

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@MikaelMayer MikaelMayer May 16, 2024 •
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I can't, as I don't understand the code at a level high enough to do that. I don't have a mental model of what ConfirmConstraint does, nor about what code context it was called with. I'll leave it for @RustanLeino to comment on it.

if (preType is PreTypeProxy) {
return false;
} else if (preType is UnusedPreType) {
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Can you add a comment to the class UnusedPreType ?

return true;
}

var pt = (DPreType)preType;
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43 changes: 43 additions & 0 deletions Source/IntegrationTests/TestFiles/LitTests/LitTest/git-issues/git-issue-5369.dfy
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@@ -0,0 +1,43 @@
// RUN: %exits-with 2 %baredafny verify %args --type-system-refresh "%s" > "%t"
// RUN: %diff "%s.expect" "%t"

ghost function f2(items: set<nat>): (r:nat)
requires |items| > 0 {
var item :| item in items;
item
}

function f(items: set<nat>) : (r:nat)
requires |items| > 0 {
//assume exists item :: item in items && forall other <- items :: item == other || item < other;
//assert exists item Smallest()
var item :| IsSmallest(items, item);
item
}

predicate IsSmallest(s: set<nat>, item: nat)
requires item in s {
m in s && forall y: nat :: y in s ==> m <= y
}

lemma Smallest(s: set<nat>) returns (m: nat)
requires s != {}
ensures m in s && IsSmallest(s, m)
decreases s
{
m :| m in s;
if y: nat :| y in s && y < m {
ghost var s' := s - {m};
assert y in s';
m := ThereIsASmallest(s');
}
}

function smallest(items: set<nat>): (r: nat)
requires |items| > 0

method m(items: set<nat>) returns (r:nat)
requires |items| > 0 {
var item :| item in items;
return item;
}
6 changes: 6 additions & 0 deletions Source/IntegrationTests/TestFiles/LitTests/LitTest/git-issues/git-issue-5369.dfy.expect
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@@ -0,0 +1,6 @@
git-issue-5369.dfy(20,2): Error: expression is not allowed to invoke a method (m)
git-issue-5369.dfy(20,40): Error: expression is not allowed to invoke a method (m)
git-issue-5369.dfy(20,42): Error: arguments to <= must have a common supertype (got int and (unused -- call to method m))
git-issue-5369.dfy(20,4): Error: expecting element type to be assignable to nat (got (unused -- call to method m))
git-issue-5369.dfy(32,9): Error: unresolved identifier: ThereIsASmallest
5 resolution/type errors detected in git-issue-5369.dfy
1 change: 1 addition & 0 deletions docs/dev/news/5369.fix
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@@ -0,0 +1 @@
Optional pre-type won't cause a crash anymore
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