Improve error when missing a comma in Apply args

[hugo-vrijswijk]

Compiler version

3.3.1

Minimized example

case class Foo(a: Int, b: Int)

object Bar:
  Foo(1 2) 

  // Or
  Foo(
    a = 1
    b = 2
  )

Output Error/Warning message

-- [E040] Syntax Error: /Users/hvanrijswijk1/ws/explore/Foo.scala:4:8 ----------
4 |  Foo(1 2) 
  |        ^
  |        ')' expected, but integer literal found

When using named arguments the error is even more confusing:

-- [E018] Syntax Error: /Users/hvanrijswijk1/ws/explore/Foo.scala:8:6 ----------
8 |    b = 2
  |      ^
  |      expression expected but = found
  |
  | longer explanation available when compiling with `-explain`
-- [E008] Not Found Error: /Users/hvanrijswijk1/ws/explore/Foo.scala:8:4 -------
7 |    a = 1
8 |    b = 2
  |        ^
  |        value b is not a member of Int.
  |        Note that `b` is treated as an infix operator in Scala 3.
  |        If you do not want that, insert a `;` or empty line in front
  |        or drop any spaces behind the operator.

Why this Error/Warning was not helpful

Following the compiler suggestion and adding a ) would just lead to another compile error, as it is expecting more arguments. It's much more likely that a , is missing.

For named arguments the first error is similar to the first when not using named arguments, but the second one is more confusing, as the suggestion of a ; does not work, nor does adding an empty line (it is already there!)

Suggested improvement

Something similar to what TypeScript does:

foo(1 2)

Error:

',' expected.

This should also work for named arguments:

Foo(
  a = 1
  b = 2
)

[nicolasstucki]

Compiling with -Xprint:parser

-- [E018] Syntax Error: t/Test.scala:9:6 ---------------------------------------
9 |    b = 2
  |      ^
  |      expression expected but = found
  |
  | longer explanation available when compiling with `-explain`
[[syntax trees at end of                    parser]] // t/Test.scala
package <empty> {
  case class Foo(val a: Int, val b: Int) {}
  module object Bar {
    Foo(1)
    Foo(a = 1 b null)
  }
}