fix: support mutable language tab configuration

src/ruby.rs

@@ -1006,7 +1006,8 @@ mod tests {
             r#"
 Vamp.configure do |c|
   c.tab_spaces = 4
-  c.language_tab_spaces = { "ruby" => 2, "makefile" => nil, "json" => 1, "yaml" => 255, "cpp" => 3, "typescriptreact" => 5 }
+  c.language_tab_spaces.merge!("ruby" => 2, "makefile" => nil, "json" => 1, "yaml" => 255, "typescriptreact" => 5)
+  c.language_tab_spaces["cpp"] = 3
 end
 "#,
         );
@@ -1069,12 +1070,18 @@ end
             for assignment in [
                 format!("c.tab_spaces = {value}"),
                 format!(r#"c.language_tab_spaces = {{ "ruby" => {value} }}"#),
+                format!(r#"c.language_tab_spaces.merge!("ruby" => {value})"#),
+                format!(r#"c.language_tab_spaces["ruby"] = {value}"#),
             ] {
                 let config = fixture.file(
                     "config.rb",
                     &format!("Vamp.configure {{ |c| {assignment} }}"),
                 );
-                assert!(load_config(&config).is_err(), "{assignment}");
+                let error = load_config(&config).unwrap_err();
+                assert!(
+                    error.contains("tab_spaces must be nil or an Integer"),
+                    "{assignment}: {error}"
+                );
             }
         }
         for value in [
@@ -1092,6 +1099,24 @@ end
         }
     }
 
+    #[test]
+    fn language_tab_space_mutations_reject_invalid_keys_before_serialization() {
+        let fixture = Fixture::new();
+        for key in [r#""""#, ":ruby", r#""\n""#, "7"] {
+            for assignment in [
+                format!("c.language_tab_spaces.merge!({key} => 2)"),
+                format!("c.language_tab_spaces[{key}] = 2"),
+            ] {
+                let config = fixture.file(
+                    "config.rb",
+                    &format!("Vamp.configure {{ |c| {assignment} }}"),
+                );
+                let error = load_config(&config).unwrap_err();
+                assert!(error.contains("Tab language"), "{assignment}: {error}");
+            }
+        }
+    }
+
     #[test]
     fn actual_ruby_dsl_context_queued_effects_and_output_isolation() {
         let fixture = Fixture::new();

src/ruby_config.rb

@@ -120,6 +120,9 @@ module Vamp
     # @return [Hash{String => Boolean, Hash{String, Symbol => Object}}] language presets/options
     attr_reader :lsp
 
+    # @return [Hash{String => Integer, nil}] LSP-style language IDs to Tab widths
+    attr_reader :language_tab_spaces
+
     # @return [Vamp::BarConfig]
     attr_reader :bar
 
@@ -265,14 +268,7 @@ module Vamp
     # @param languages [Hash{String => Integer, nil}] LSP-style language IDs to Tab widths
     # @return [Hash{String => Integer, nil}]
     def language_tab_spaces=(languages)
-      raise TypeError, "language_tab_spaces must be a Hash" unless languages.is_a?(Hash)
-
-      @language_tab_spaces = languages.to_h do |language, spaces|
-        language = nonempty_string!(language, "Tab language")
-        raise ArgumentError, "Tab language must not contain control characters" if language.match?(/[[:cntrl:]]/)
-
-        [language, tab_spaces!(spaces)]
-      end
+      @language_tab_spaces = language_tab_spaces!(languages)
     end
 
     # @param lines [Integer] nonnegative context lines around each diff change
@@ -350,7 +346,7 @@ module Vamp
         "highlight_trailing_whitespace" => @highlight_trailing_whitespace,
         "whitespace_characters" => @whitespace_characters,
         "whitespace_scope" => @whitespace_scope,
-        "tab_spaces" => @tab_spaces, "language_tab_spaces" => @language_tab_spaces,
+        "tab_spaces" => @tab_spaces, "language_tab_spaces" => language_tab_spaces!(@language_tab_spaces),
         "top_bar" => @bar.top, "bottom_bar" => @bar.bottom, "labels" => @labels,
         "popup" => { "command" => @popup.command, "search" => @popup.search },
         "diff_context_lines" => @diff_context_lines, "diff_expand_lines" => @diff_expand_lines,
@@ -369,6 +365,19 @@ module Vamp
       spaces
     end
 
+    # @param languages [Hash{String => Integer, nil}]
+    # @return [Hash{String => Integer, nil}]
+    def language_tab_spaces!(languages)
+      raise TypeError, "language_tab_spaces must be a Hash" unless languages.is_a?(Hash)
+
+      languages.to_h do |language, spaces|
+        language = nonempty_string!(language, "Tab language")
+        raise ArgumentError, "Tab language must not contain control characters" if language.match?(/[[:cntrl:]]/)
+
+        [language, tab_spaces!(spaces)]
+      end
+    end
+
     # @param value [Integer]
     # @param label [String]
     # @param minimum [Integer]