Pull Request Description

Most sequences of operator characters are lexed as a single operator; however, there is a special case when the last character is - in order to accept expressions such as x+-1 and x=-1, which use a binary operator followed by a unary operator, in an unspaced subexpression.

Due to this lexical special case, special handling is needed in the parser to reject some related invalid syntaxes, such as x +- 1 and x =- 1. This special handling was absent, resulting in reaching a debug assertion when such syntax errors were encountered (#7335). This PR corrects the assumption in parts of the parser that multiple consecutive operators cannot occur in unspaced subexpressions. See the newly-added test cases for examples of the rejected expressions.

Important Notes

• Note to QA tester: I have tested that, for every .enso file in the repo, this PR does not change the parser's AST. If there are any regressions, they would relate to inputs that are poor style or syntax errors, both of which are not as thoroughly covered by .enso tests and library files.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.