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OndrejSpanel opened this issue Apr 11, 2025 · 0 comments · Fixed by #22977
Closed

False positive warning: unused import when var symbol is used only as assignment target #22970

OndrejSpanel opened this issue Apr 11, 2025 · 0 comments · Fixed by #22977
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@som-snytt
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area:linting Linting warnings enabled with -W or -Xlint itype:bug

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@OndrejSpanel
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OndrejSpanel commented Apr 11, 2025 •
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Compiler version

3.7.0-RC1
3.7.0-RC2

Minimized code

Compile with -Wunused:imports:

object X {
  var global = 0
}

object Main {
  import X.global
  def main(args: Array[String]): Unit = {
    global = 1
  }
}

Output

unused import
  import X.global

Expectation

The warning should not be there. The code requires the import to compile.
@OndrejSpanel OndrejSpanel added itype:bug stat:needs triage Every issue needs to have an "area" and "itype" label labels Apr 11, 2025
@OndrejSpanel OndrejSpanel changed the title False position: unused import when var symbol is used only as assignment target False positive warning: unused import when var symbol is used only as assignment target Apr 11, 2025
@som-snytt som-snytt added area:linting Linting warnings enabled with -W or -Xlint and removed stat:needs triage Every issue needs to have an "area" and "itype" label labels Apr 11, 2025
@som-snytt som-snytt self-assigned this Apr 11, 2025
@som-snytt som-snytt mentioned this issue Apr 11, 2025
Merged
tgodzik pushed a commit that referenced this issue May 7, 2025
@som-snytt
Improve checking LHS of Assign (#22977)
9bee756 
Fixes #22970

Simple example showing how awkward this is compared to a traversal,
where there is more control when descending.

Previously, it "ignored" the LHS of Assign to avoid taking `x = y` as
ref to `x` instead of assignment to.

Now, "mark" the LHS as assignment, so `transformIdent` and `Select` set
a "mode" flag, such that `x` is correctly taken as either a ref or
assign to `x`.

Probably there is more complex syntax to handle as LHS, but I haven't
had coffee yet.
tgodzik pushed a commit to scala/scala3-lts that referenced this issue May 12, 2025
@som-snytt @tgodzik
Improve checking LHS of Assign (scala#22977)
fcfe738 
Fixes scala#22970

Simple example showing how awkward this is compared to a traversal,
where there is more control when descending.

Previously, it "ignored" the LHS of Assign to avoid taking `x = y` as
ref to `x` instead of assignment to.

Now, "mark" the LHS as assignment, so `transformIdent` and `Select` set
a "mode" flag, such that `x` is correctly taken as either a ref or
assign to `x`.

Probably there is more complex syntax to handle as LHS, but I haven't
had coffee yet.
[Cherry-picked 9bee756]
odersky pushed a commit to dotty-staging/dotty that referenced this issue May 12, 2025
@som-snytt @odersky
Improve checking LHS of Assign (scala#22977)
108b941 
Fixes scala#22970

Simple example showing how awkward this is compared to a traversal,
where there is more control when descending.

Previously, it "ignored" the LHS of Assign to avoid taking `x = y` as
ref to `x` instead of assignment to.

Now, "mark" the LHS as assignment, so `transformIdent` and `Select` set
a "mode" flag, such that `x` is correctly taken as either a ref or
assign to `x`.

Probably there is more complex syntax to handle as LHS, but I haven't
had coffee yet.
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Improve checking LHS of Assign som-snytt/dotty
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