fix(linter): lingering linter diagnostics

Fixes #706

Author: gnikit

CHANGELOG.md

@@ -74,6 +74,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+- Fixed bug where diagnostic messages would linger from the previous state
+  ([#706](https://github.com/fortran-lang/vscode-fortran-support/issues/706))
 - Fixed activation bug on Windows causing the persistent cache to fail
   ([#700](https://github.com/fortran-lang/vscode-fortran-support/issues/700))
 - Fixed bug where the linter's internal cache directory would not always exist

src/features/linter-provider.ts

@@ -329,8 +329,12 @@ export class FortranLintingProvider {
     if (!isFortran(document)) return;
 
     const output = await this.doBuild(document);
-    if (!output) return;
-
+    if (!output) {
+      // If the linter output is now empty, then there are no errors.
+      // Discard the previous diagnostic state for this document
+      if (this.fortranDiagnostics.has(document.uri)) this.fortranDiagnostics.delete(document.uri);
+      return;
+    }
     let diagnostics: vscode.Diagnostic[] = this.linter.parse(output);
     // Remove duplicates from the diagnostics array
     diagnostics = [...new Map(diagnostics.map(v => [JSON.stringify(v), v])).values()];