Parser: Allow inline case/when and case/in in strict mode

[marcoroth]

This pull request updates the parser to provide backwards compatibility for <% case @foo when :bar %> (case/when or case/in in a single ERB tag) by gating the ERBCaseWithConditionsError behind strict mode.

This syntax is valid Erubi and, for backwards compatibility reasons, we should also make this also work in Herb. With this change, non-strict now mode accepts this syntax and now correctly compiles it by splitting a the single ERB Node into multiple AST nodes by creating a new synthetic ERBWhenNode or ERBCaseInNode node.

The following template:

<% case count
   in 1 %>
  One
<% in 2 %>
  Two
<% end %>

Now gets parsed as this in non-strict mode:

@ DocumentNode (location: (1:0)-(7:0))
└── children: (2 items)
    ├── @ ERBCaseMatchNode (location: (1:0)-(6:9))
    │   ├── tag_opening: "<%" (location: (1:0)-(1:2))
    │   ├── content: " case count
    │      in 1 " (location: (1:2)-(2:8))
    │   ├── tag_closing: "%>" (location: (2:8)-(2:10))
    │   ├── children: []
    │   ├── conditions: (2 items)
    │   │   ├── @ ERBInNode (location: (2:10)-(4:0))
    │   │   │   ├── tag_opening: ∅
    │   │   │   ├── content: ∅
    │   │   │   ├── tag_closing: ∅
    │   │   │   ├── then_keyword: ∅
    │   │   │   └── statements: (1 item)
    │   │   │       └── @ HTMLTextNode (location: (2:10)-(4:0))
    │   │   │           └── content: "\n  One\n"
    │   │   │
    │   │   └── @ ERBInNode (location: (4:0)-(4:10))
    │   │       ├── tag_opening: "<%" (location: (4:0)-(4:2))
    │   │       ├── content: " in 2 " (location: (4:2)-(4:8))
    │   │       ├── tag_closing: "%>" (location: (4:8)-(4:10))
    │   │       ├── then_keyword: ∅
    │   │       └── statements: (1 item)
    │   │           └── @ HTMLTextNode (location: (4:10)-(6:0))
    │   │               └── content: "\n  Two\n"
    │   │
    │   ├── else_clause: ∅
    │   └── end_node:
    │       └── @ ERBEndNode (location: (6:0)-(6:9))
    │           ├── tag_opening: "<%" (location: (6:0)-(6:2))
    │           ├── content: " end " (location: (6:2)-(6:7))
    │           └── tag_closing: "%>" (location: (6:7)-(6:9))
    │
    └── @ HTMLTextNode (location: (6:9)-(7:0))
        └── content: "\n"

In strict mode it will still produce a ERBCaseWithConditionsError.

Before this change, it was parsed as:

@ DocumentNode (location: (1:0)-(7:0))
└── children: (2 items)
    ├── @ ERBCaseMatchNode (location: (1:0)-(6:9))
    │   ├── errors: (1 error)
    │   │   └── @ ERBCaseWithConditionsError (location: (1:0)-(2:10))
    │   │       └── message: "A `case` statement with `when`/`in` in a single ERB tag cannot be formatted. Use separate tags for `case` and its conditions."
    │   │
    │   ├── tag_opening: "<%" (location: (1:0)-(1:2))
    │   ├── content: " case count
    │      in 1 " (location: (1:2)-(2:8))
    │   ├── tag_closing: "%>" (location: (2:8)-(2:10))
    │   ├── children: (1 item)
    │   │   └── @ HTMLTextNode (location: (2:10)-(4:0))
    │   │       └── content: "\n  One\n"
    │   │
    │   ├── conditions: (1 item)
    │   │   └── @ ERBInNode (location: (4:0)-(4:10))
    │   │       ├── tag_opening: "<%" (location: (4:0)-(4:2))
    │   │       ├── content: " in 2 " (location: (4:2)-(4:8))
    │   │       ├── tag_closing: "%>" (location: (4:8)-(4:10))
    │   │       ├── then_keyword: ∅
    │   │       └── statements: (1 item)
    │   │           └── @ HTMLTextNode (location: (4:10)-(6:0))
    │   │               └── content: "\n  Two\n"
    │   │
    │   ├── else_clause: ∅
    │   └── end_node:
    │       └── @ ERBEndNode (location: (6:0)-(6:9))
    │           ├── tag_opening: "<%" (location: (6:0)-(6:2))
    │           ├── content: " end " (location: (6:2)-(6:7))
    │           └── tag_closing: "%>" (location: (6:7)-(6:9))
    │
    └── @ HTMLTextNode (location: (6:9)-(7:0))
        └── content: "\n"

Resolves #1252
Related #1112

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commit: 9f9a9e5

[github-actions]

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