frontend: implement basic scope analysis

frontend/src/main/kotlin/gay/pizza/pork/frontend/World.kt

@@ -9,6 +9,7 @@ import gay.pizza.pork.parser.Tokenizer
 
 class World(val importSource: ImportSource) {
   private val internalUnits = mutableMapOf<String, CompilationUnit>()
+  private val importedUnits = mutableMapOf<CompilationUnit, Set<CompilationUnit>>()
 
   val units: List<CompilationUnit>
     get() = internalUnits.values.toList()
@@ -37,6 +38,7 @@ class World(val importSource: ImportSource) {
       val importedUnit = loadOneUnit(importLocator)
       units.add(importedUnit)
     }
+    importedUnits[unit] = units
     return units
   }
 
@@ -46,6 +48,9 @@ class World(val importSource: ImportSource) {
     return unit
   }
 
+  fun importedBy(unit: CompilationUnit): Set<CompilationUnit> =
+    importedUnits[unit] ?: emptySet()
+
   private fun pickContentSource(form: String): ContentSource =
     importSource.provideContentSource(form)
 

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/CompilationUnitScope.kt

@@ -0,0 +1,36 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.CompilationUnit
+import gay.pizza.pork.ast.Symbol
+
+class CompilationUnitScope(val worldScope: WorldScope, val unit: CompilationUnit) {
+  val externalSymbols = mutableSetOf<ScopeSymbol>()
+  val internalSymbols = mutableSetOf<ScopeSymbol>()
+
+  fun index() {
+    for (definition in unit.definitions) {
+      val scopeSymbol = ScopeSymbol(unit, definition)
+      if (definition.modifiers.export) {
+        externalSymbols.add(scopeSymbol)
+      }
+      internalSymbols.add(scopeSymbol)
+    }
+  }
+
+  fun findInternallyVisibleSymbols(): Set<VisibleScopeSymbol> {
+    val allSymbols = mutableMapOf<Symbol, VisibleScopeSymbol>()
+    val imports = worldScope.world.importedBy(unit)
+    for (import in imports) {
+      val scope = worldScope.index(import)
+      for (importedSymbol in scope.externalSymbols) {
+        allSymbols[importedSymbol.symbol] = VisibleScopeSymbol(unit, importedSymbol)
+      }
+    }
+
+    for (internalSymbol in internalSymbols) {
+      allSymbols[internalSymbol.symbol] = VisibleScopeSymbol(unit, internalSymbol)
+    }
+
+    return allSymbols.values.toSet()
+  }
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/ScopeSymbol.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.Definition
+import gay.pizza.pork.ast.Node
+
+class ScopeSymbol(
+  val compilationUnit: Node,
+  val definition: Definition
+) {
+  val symbol = definition.symbol
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/VisibleScopeSymbol.kt

@@ -0,0 +1,8 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.CompilationUnit
+
+class VisibleScopeSymbol(val visibleToUnit: CompilationUnit, val scopeSymbol: ScopeSymbol) {
+  val isInternalSymbol: Boolean
+    get() = visibleToUnit == scopeSymbol.compilationUnit
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/WorldScope.kt

@@ -0,0 +1,24 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.CompilationUnit
+import gay.pizza.pork.frontend.World
+
+class WorldScope(val world: World) {
+  private val compilationUnitScopes = mutableMapOf<CompilationUnit, CompilationUnitScope>()
+
+  fun indexAll() {
+    for (unit in world.units) {
+      index(unit)
+    }
+  }
+
+  fun index(unit: CompilationUnit): CompilationUnitScope =
+    scope(unit).apply {
+      index()
+    }
+
+  fun scope(unit: CompilationUnit): CompilationUnitScope =
+    compilationUnitScopes.computeIfAbsent(unit) {
+      CompilationUnitScope(this, unit)
+    }
+}