Use other tree for actual symbol of Assign #22869

som-snytt · 2025-03-25T08:19:23Z

Find a name for the error message.

hamzaremmal · 2025-03-28T13:24:49Z

compiler/src/dotty/tools/dotc/reporting/messages.scala

+        |Also, assignment syntax can be used if there is a corresponding setter:
+        |  ${hl("def")} ${name}${hl("_=(x: Int): Unit = _v = x")}


I wouldn't add this one here. The sugaring for setters is very very scope specific and fragile. It cannot be summarized into the assignment syntax can be used if there is a corresponding setter...

I think some words are necessary for user who needs an explanation; I restricted it to class members.

hamzaremmal · 2025-03-28T13:27:17Z

compiler/src/dotty/tools/dotc/reporting/messages.scala

 class ReassignmentToVal(name: Name)(using Context)
  extends TypeMsg(ReassignmentToValID) {
-  def msg(using Context) = i"""Reassignment to val $name"""
+  def msg(using Context) = i"""Reassignment to value $name"""


We could actually pass the symbol instead of the name and we would either get val, def,... depending on the actual symbol.

som-snytt · 2025-03-28T16:20:39Z

I started down the long tail of polishing words.

Let the symbol say what it is, and restrict setter explanation to class-owned symbols. (Need to check class params.)

som-snytt · 2025-07-24T20:05:19Z

Updated the branch from March, which had the spree contributors.

Improved to include the pathology from neg/assignments: x_= = 42. Some words for the user, and also don't try to format a message such as var x_=_= or similar, which throws in the formatter.

That test also suggested providing the args, which I took to mean show x_=(42).

I ran out of steam and did not add the scala 2 explanation, that x += 1 "does not convert to assignment" because the x is not mutable. The existing message that "it doesn't have a += member" is confusing, not only to beginners.

hamzaremmal · 2025-09-22T20:14:21Z

tests/neg/i22671.check

+-- [E052] Type Error: tests/neg/i22671.scala:20:4 ----------------------------------------------------------------------
+20 |  y = 27 // error
+   |  ^^^^^^
+   |  Assignment to method x


Seems like the renaming isn't taken into account here.

I think that was intentional, though it could be improved

Assignment to y which is a renaming of method x

or

Assignment to method x imported as y // closer to user syntax

odersky

I think this PR would profit from a discussion on concrete test cases what the error message should be. Concentrate in common test cases not obscure ones. Obscure code does not warrant much work to make clear error messages.

So, can we break out the test files into a comment, show what the current message is, and what the suggested error message should be?

odersky · 2025-10-15T08:49:55Z

tests/neg/assignments.check

+-- [E052] Type Error: tests/neg/assignments.scala:17:8 -----------------------------------------------------------------
+17 |    x_= = 2  // error should give missing arguments, was: Reassignment to val x_=
+   |    ^^^^^^^
+   |    Bad assignment to setter should use x_=(2)


Sorry, I don't see how this is an improvement. Who in their right minds would write x_= =? That's just not what I see, and we should not special case it.

That was an existing test. And little cost to cover the case.

odersky · 2025-10-15T08:50:44Z

tests/neg/i11561.check

 3 |  val updateText2 = copy(text = (_: String)) // error
  |                         ^^^^^^^^^^^^^^^^^^
-  |                         Reassignment to val text
+  |                         Assignment to value text


I find "Reassignment to val" much clearer than "Assignment to value".

Co-authored-by: Jan-Pieter van den Heuvel <[email protected]> Co-authored-by: Seth Tisue <[email protected]> Co-authored-by: Lucas Nouguier <[email protected]> Co-authored-by: Prince <[email protected]>

som-snytt · 2025-10-15T14:45:05Z

The PR includes only the fix for the issue and not the semester project in psychology of programming.

I think "reassignment to val" is merely familiar and corresponds to a certain mental model (that initialization or definition is one assignment, and a subsequent use of = is a "reassignment"). If only we had :=.

The goal was parity with Scala 2, where errors in assignment operators += can be obscure, especially because it may be "not a member" or it may be that the rewrite failed for some other reason.

som-snytt mentioned this pull request Mar 25, 2025

Better selection of name for ReassignmentToVal error message #22823

Closed

som-snytt force-pushed the issue/22671-assignment-error branch from cbdcdd5 to ef97824 Compare March 25, 2025 14:57

ajafri2001 mentioned this pull request Mar 28, 2025

bugfix : Show correct error message when mutating def #22880

Closed

hamzaremmal reviewed Mar 28, 2025

View reviewed changes

som-snytt force-pushed the issue/22671-assignment-error branch from ef97824 to 76c6790 Compare March 28, 2025 16:09

som-snytt force-pushed the issue/22671-assignment-error branch 2 times, most recently from 7785a12 to 21d48c8 Compare March 29, 2025 21:37

som-snytt force-pushed the issue/22671-assignment-error branch from 21d48c8 to 1187728 Compare July 24, 2025 19:55

som-snytt force-pushed the issue/22671-assignment-error branch from 1187728 to fb79c19 Compare July 24, 2025 20:16

som-snytt marked this pull request as ready for review July 24, 2025 20:17

Gedochao requested a review from hamzaremmal July 25, 2025 05:31

Gedochao assigned hamzaremmal Jul 25, 2025

hamzaremmal requested changes Sep 22, 2025

View reviewed changes

som-snytt force-pushed the issue/22671-assignment-error branch from fb79c19 to a9a08b4 Compare September 22, 2025 22:06

som-snytt mentioned this pull request Oct 15, 2025

Better error message: reassignment to val #24184

Open

odersky reviewed Oct 15, 2025

View reviewed changes

Use other tree for actual symbol of Assign

b40dc93

Co-authored-by: Jan-Pieter van den Heuvel <[email protected]> Co-authored-by: Seth Tisue <[email protected]> Co-authored-by: Lucas Nouguier <[email protected]> Co-authored-by: Prince <[email protected]>

som-snytt force-pushed the issue/22671-assignment-error branch from a9a08b4 to b40dc93 Compare October 15, 2025 14:39

		\|Also, assignment syntax can be used if there is a corresponding setter:
		\| ${hl("def")} ${name}${hl("_=(x: Int): Unit = _v = x")}

Use other tree for actual symbol of Assign #22869

Are you sure you want to change the base?

Use other tree for actual symbol of Assign #22869

Conversation

som-snytt commented Mar 25, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

som-snytt commented Mar 28, 2025

Uh oh!

som-snytt commented Jul 24, 2025

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

odersky left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

odersky Oct 15, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

som-snytt commented Oct 15, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

som-snytt commented Mar 25, 2025 •

edited

Loading

odersky Oct 15, 2025 •

edited

Loading

som-snytt commented Oct 15, 2025 •

edited

Loading