fix(linter): let file-header disable directives suppress file-start diagnostics

Author: camc314

apps/oxlint/test/fixtures/basic_with_disable_directive_file_start/.oxlintrc.json

@@ -0,0 +1,6 @@
+{
+  "jsPlugins": ["./plugin.ts"],
+  "rules": {
+    "basic-custom-plugin/rule": "error"
+  }
+}

apps/oxlint/test/fixtures/basic_with_disable_directive_file_start/files/index.js

@@ -0,0 +1 @@
+/* oxlint-disable basic-custom-plugin/rule */

apps/oxlint/test/fixtures/basic_with_disable_directive_file_start/plugin.ts

@@ -0,0 +1,25 @@
+import type { Plugin } from "#oxlint/plugins";
+
+const plugin: Plugin = {
+  meta: {
+    name: "basic-custom-plugin",
+  },
+  rules: {
+    rule: {
+      create(_context) {
+        return {
+          Program(_program) {
+            _context.report({
+              message: "oops",
+              loc: {
+                start: { line: 0, column: 0 },
+              },
+            });
+          },
+        };
+      },
+    },
+  },
+};
+
+export default plugin;

crates/oxc_linter/src/disable_directives.rs

@@ -377,7 +377,9 @@ impl DisableDirectivesBuilder {
                 // `eslint-disable`
                 if text.trim().is_empty() {
                     if self.disable_all_start.is_none() {
-                        self.disable_all_start = Some((comment_span.end, comment_span));
+                        // Start coverage at the beginning of the directive comment so
+                        // top-of-file headers can suppress file-start diagnostics.
+                        self.disable_all_start = Some((comment.span.start, comment_span));
                     }
                     self.disable_rule_comments.push(DisableRuleComment {
                         span: comment_span,
@@ -493,7 +495,7 @@ impl DisableDirectivesBuilder {
                     let mut rules = vec![];
                     Self::get_rule_names(text, rule_name_start, |rule_name, name_span| {
                         self.disable_start_map.entry(rule_name.to_string()).or_insert((
-                            comment_span.end,
+                            comment.span.start,
                             name_span,
                             comment_span,
                         ));
@@ -1391,4 +1393,20 @@ function test() {
             "eslint-disable-next-line should NOT suppress diagnostics on lines after the next line"
         );
     }
+
+    #[test]
+    fn test_disable_file_header_suppresses_file_start_diagnostic() {
+        test_directives(
+            |prefix| {
+                format!(
+                    "/* {prefix}-disable no-console */\nconsole.log('still disabled by header');\n"
+                )
+            },
+            |_, directives| {
+                // Some rules report at file start (line 1, column 0), e.g. Program-level diagnostics.
+                // A header disable should still suppress those diagnostics.
+                assert!(directives.contains("no-console", Span::new(0, 1)));
+            },
+        );
+    }
 }