build_assets.rs: Add code to track dependents of each syntax

This information is useful when you want to build several SyntaxSets, but
without having to duplicate SyntaxDefinitions. For example:

"Rust" has no dependencies. But "Markdown" depends on "Rust". With the data
structures this code adds, we know that "Rust" is a dependent syntax for
"Markdown", and can construct a SyntaxSet that takes that into account.

Note that code has a temporary environment flag to ignore any information about
dependents when constructing SyntaxSets. Code that makes use of the new data
structure will be added later.

src/assets/build_assets.rs

@@ -16,6 +16,9 @@ type OtherSyntaxLookup<'a> = HashMap<OtherSyntax, &'a SyntaxDefinition>;
 /// Used to look up what dependencies a given [SyntaxDefinition] has
 type SyntaxToDependencies = HashMap<SyntaxName, Vec<OtherSyntax>>;
 
+/// Used to look up what other [SyntaxDefinition]s depend on a given [SyntaxDefinition]
+type SyntaxToDependents<'a> = HashMap<SyntaxName, Vec<OtherSyntax>>;
+
 /// Represents some other `*.sublime-syntax` file, i.e. another [SyntaxDefinition].
 #[derive(Debug, Eq, PartialEq, Clone, Hash)]
 enum OtherSyntax {
@@ -215,7 +218,8 @@ fn build_minimal_syntax_sets(
     let syntaxes = syntax_set_builder.syntaxes();
 
     // Build the data structures we need for dependency resolution
-    let (other_syntax_lookup, syntax_to_dependencies) = generate_maps(syntaxes);
+    let (other_syntax_lookup, syntax_to_dependencies, syntax_to_dependents) =
+        generate_maps(syntaxes);
 
     // Create one minimal SyntaxSet from each (non-hidden) SyntaxDefinition
     syntaxes.iter().filter_map(move |syntax| {
@@ -224,7 +228,12 @@ fn build_minimal_syntax_sets(
         }
 
         let mut builder = SyntaxSetDependencyBuilder::new();
-        builder.add_with_dependencies(syntax, &other_syntax_lookup, &syntax_to_dependencies);
+        builder.add_with_dependencies(
+            syntax,
+            &other_syntax_lookup,
+            &syntax_to_dependencies,
+            &syntax_to_dependents,
+        );
         let syntax_set = builder.build();
 
         if std::env::var("BAT_PRINT_SYNTAX_DEPENDENCIES").is_ok() {
@@ -237,22 +246,48 @@ fn build_minimal_syntax_sets(
     })
 }
 
-/// In order to analyze dependencies, we need two key pieces of data.
-/// First, when we have a [OtherSyntax], we need to know what [SyntaxDefinition] that
-/// corresponds to. Second, when we have a [SyntaxDefinition], we need to know
-/// what dependencies it has. This functions generates that data for each syntax.
-fn generate_maps(syntaxes: &[SyntaxDefinition]) -> (OtherSyntaxLookup, SyntaxToDependencies) {
+/// In order to analyze dependencies, we need three key pieces of data.
+///
+///  * When we have a [OtherSyntax], we need to know what [SyntaxDefinition]
+///    that corresponds to
+///  * When we have a [SyntaxDefinition], we need to know what dependencies it
+///    has
+///  * When we have a [SyntaxDefinition], we need to know what other syntaxes
+///    depend on it
+///
+/// This functions generates that data for each syntax.
+fn generate_maps(
+    syntaxes: &[SyntaxDefinition],
+) -> (OtherSyntaxLookup, SyntaxToDependencies, SyntaxToDependents) {
     let mut other_syntax_lookup = HashMap::new();
     let mut syntax_to_dependencies = HashMap::new();
+    let mut syntax_to_dependents = HashMap::new();
 
     for syntax in syntaxes {
-        syntax_to_dependencies.insert(syntax.name.clone(), dependencies_for_syntax(syntax));
-
         other_syntax_lookup.insert(OtherSyntax::ByName(syntax.name.clone()), syntax);
         other_syntax_lookup.insert(OtherSyntax::ByScope(syntax.scope), syntax);
     }
 
-    (other_syntax_lookup, syntax_to_dependencies)
+    for syntax in syntaxes {
+        let dependencies = dependencies_for_syntax(syntax);
+
+        for dependency in &dependencies {
+            if let Some(dependency) = other_syntax_lookup.get(dependency) {
+                syntax_to_dependents
+                    .entry(dependency.name.clone())
+                    .or_insert_with(Vec::new)
+                    .push(OtherSyntax::ByName(syntax.name.clone()));
+            }
+        }
+
+        syntax_to_dependencies.insert(syntax.name.clone(), dependencies);
+    }
+
+    (
+        other_syntax_lookup,
+        syntax_to_dependencies,
+        syntax_to_dependents,
+    )
 }
 
 /// Gets what external dependencies a given [SyntaxDefinition] has.
@@ -322,6 +357,7 @@ impl SyntaxSetDependencyBuilder {
         syntax: &SyntaxDefinition,
         other_syntax_lookup: &OtherSyntaxLookup,
         syntax_to_dependencies: &SyntaxToDependencies,
+        syntax_to_dependents: &SyntaxToDependents,
     ) {
         let name = &syntax.name;
         if self.is_syntax_already_added(name) {
@@ -330,18 +366,23 @@ impl SyntaxSetDependencyBuilder {
 
         self.syntax_set_builder.add(syntax.clone());
 
-        let dependencies = syntax_to_dependencies.get(name);
-        if dependencies.is_none() {
-            eprintln!("ERROR: Unknown dependencies for {}", name);
-            return;
+        let mut syntaxes_to_add = vec![];
+        if let Some(dependencies) = syntax_to_dependencies.get(name) {
+            syntaxes_to_add.extend(dependencies);
         }
-
-        for dependency in dependencies.unwrap() {
-            if let Some(syntax_definition_dependency) = other_syntax_lookup.get(dependency) {
+        if let Some(dependents) = syntax_to_dependents.get(name) {
+            // This will later be enabled intelligently
+            if std::env::var("BAT_INCLUDE_SYNTAX_DEPENDENTS").is_ok() {
+                syntaxes_to_add.extend(dependents);
+            }
+        }
+        for syntax_to_add in syntaxes_to_add {
+            if let Some(syntax_to_add) = other_syntax_lookup.get(syntax_to_add) {
                 self.add_with_dependencies(
-                    syntax_definition_dependency,
+                    syntax_to_add,
                     other_syntax_lookup,
                     syntax_to_dependencies,
+                    syntax_to_dependents,
                 )
             }
         }