ERB injection for other source languages (#113)

ERB can be used to template any kind of source file — not just HTML.
However, it’s most commonly used for generating HTML, YAML and Ruby
source.

This PR updates the `ERB` language to be more generic, treating `.erb`
files as plain text with Ruby injections within the ERB template tags.

It then introduces two new languages: `HTML/ERB` and `YAML/ERB`, which
handle switching between HTML and Ruby and YAML and Ruby respectively.

I attempted to make a specialised language for `Ruby/ERB`, but couldn’t
get past some basic syntax highlighting issues. I think it’s quite
reasonable to highlight `.rb.erb` files as plain text with Ruby inside
the ERB tags since it would be very difficult to guess at how the
generated Ruby will look structurally. It’s certainly an improvement on
treating it like HTML.

I’ve configured mappings from `ERB`, `HTML/ERB` and `YAML/ERB` for Ruby
LSP, which will handle them all as `erb`. I’ve also updated the Herb LSP
to handle `HTML/ERB` files specifically.

### Next steps

I would be nice if the YAML language server was configured to run on
`YAML/ERB` files. I believe this can be done by updating [this
file](https://github.com/zed-industries/zed/blob/a067c16c823354da63966273ac15d1aa93c0e922/crates/languages/src/lib.rs).

However, I don’t think this is a blocker as most YAML/ERB files are
actually named `.yml` not `.yml.erb` and so will be treated as regular
old YAML files.

Author: joeldrapper

extension.toml

@@ -12,7 +12,13 @@ languages = ["Ruby"]
 
 [language_servers.ruby-lsp]
 name = "Ruby LSP"
-languages = ["Ruby", "ERB"]
+languages = ["Ruby", "ERB", "HTML/ERB", "YAML/ERB"]
+
+[language_servers.ruby-lsp.language_ids]
+"Ruby" = "ruby"
+"ERB" = "erb"
+"HTML/ERB" = "erb"
+"YAML/ERB" = "erb"
 
 [language_servers.rubocop]
 name = "Rubocop"
@@ -28,7 +34,7 @@ languages = ["Ruby"]
 
 [language_servers.herb]
 name = "Herb"
-languages = ["ERB"]
+languages = ["HTML/ERB"]
 
 [grammars.ruby]
 repository = "https://github.com/tree-sitter/tree-sitter-ruby"

languages/erb/config.toml

@@ -1,7 +1,3 @@
 name = "ERB"
 grammar = "embedded_template"
 path_suffixes = ["erb"]
-autoclose_before = ">})"
-brackets = [{ start = "<", end = ">", close = true, newline = true }]
-block_comment = ["<%#", "%>"]
-word_characters = ["?", "!"]

languages/erb/injections.scm

@@ -3,5 +3,5 @@
   (#set! "combined"))
 
 ((content) @content
-  (#set! "language" "html")
+  (#set! "language" "plaintext")
   (#set! "combined"))

languages/html-erb/config.toml

@@ -0,0 +1,7 @@
+name = "HTML/ERB"
+grammar = "embedded_template"
+path_suffixes = ["html.erb"]
+autoclose_before = ">})"
+brackets = [{ start = "<", end = ">", close = true, newline = true }]
+block_comment = ["<%#", "%>"]
+word_characters = ["?", "!"]

languages/html-erb/highlights.scm

@@ -0,0 +1,12 @@
+(comment_directive) @comment
+
+[
+  "<%#"
+  "<%"
+  "<%="
+  "<%_"
+  "<%-"
+  "%>"
+  "-%>"
+  "_%>"
+] @keyword

languages/html-erb/injections.scm

@@ -0,0 +1,7 @@
+((code) @content
+  (#set! "language" "ruby")
+  (#set! "combined"))
+
+((content) @content
+  (#set! "language" "html")
+  (#set! "combined"))

languages/yaml-erb/config.toml

@@ -0,0 +1,3 @@
+name = "YAML/ERB"
+grammar = "embedded_template"
+path_suffixes = ["yml.erb", "yaml.erb"]

languages/yaml-erb/highlights.scm

@@ -0,0 +1,12 @@
+(comment_directive) @comment
+
+[
+  "<%#"
+  "<%"
+  "<%="
+  "<%_"
+  "<%-"
+  "%>"
+  "-%>"
+  "_%>"
+] @keyword

languages/yaml-erb/injections.scm

@@ -0,0 +1,7 @@
+((code) @content
+  (#set! "language" "ruby")
+  (#set! "combined"))
+
+((content) @content
+  (#set! "language" "yaml")
+  (#set! "combined"))