[analyzer] Add LinterContext.currentUnit and use it for content in eol_at_end_of_file

... instead of potentially reading the file from disk.

Fixes #59704

Change-Id: Id5939dce4d11429a929a4b63611ff1823449b64c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/401424
Reviewed-by: Phil Quitslund <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: DanTup

pkg/analysis_server/lib/src/services/correction/bulk_fix_processor.dart

@@ -565,6 +565,7 @@ class BulkFixProcessor {
     }
 
     // Run lints that handle specific node types.
+    context.currentUnit = currentUnit;
     currentUnit.unit.accept(AnalysisRuleVisitor(nodeRegistry));
   }
 

pkg/analysis_server_plugin/lib/src/plugin_server.dart

@@ -300,6 +300,7 @@ class PluginServer {
       }
     }
 
+    context.currentUnit = currentUnit;
     currentUnit.unit.accept(
         AnalysisRuleVisitor(nodeRegistry, shouldPropagateExceptions: true));
     // The list of the `AnalysisError`s and their associated

pkg/analyzer/lib/src/dart/analysis/library_analyzer.dart

@@ -415,6 +415,7 @@ class LibraryAnalyzer {
       }
 
       // Run lint rules that handle specific node types.
+      context.currentUnit = currentUnit;
       unit.accept(
         AnalysisRuleVisitor(
           nodeRegistry,

pkg/analyzer/lib/src/lint/linter.dart

@@ -36,6 +36,12 @@ abstract class LinterContext {
   /// including the defining compilation unit, all parts, and all augmentations.
   List<LintRuleUnitContext> get allUnits;
 
+  /// The compilation unit being linted.
+  ///
+  /// `null` when a unit is not currently being linted (for example when node
+  /// processors are being registered).
+  LintRuleUnitContext? get currentUnit;
+
   /// The defining compilation unit of the library under analysis.
   LintRuleUnitContext get definingUnit;
 
@@ -80,6 +86,9 @@ final class LinterContextWithParsedResults implements LinterContext {
   @override
   final LintRuleUnitContext definingUnit;
 
+  @override
+  LintRuleUnitContext? currentUnit;
+
   @override
   final InheritanceManager3 inheritanceManager = InheritanceManager3();
 
@@ -121,6 +130,9 @@ final class LinterContextWithResolvedResults implements LinterContext {
   @override
   final LintRuleUnitContext definingUnit;
 
+  @override
+  LintRuleUnitContext? currentUnit;
+
   @override
   final WorkspacePackage? package;
 

pkg/linter/lib/src/rules/eol_at_end_of_file.dart

@@ -35,7 +35,8 @@ class _Visitor extends SimpleAstVisitor<void> {
 
   @override
   void visitCompilationUnit(CompilationUnit node) {
-    var content = node.declaredFragment?.source.contents.data;
+    assert(context.currentUnit?.unit == node);
+    var content = context.currentUnit?.content;
     if (content != null &&
         content.isNotEmpty &&
         // TODO(srawlins): Re-implement this check without iterating over