feat: Remove duplicate diagnostics from linter

Fixes #598

Author: gnikit

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Changed
+
+- Removes duplicate diagnostic messages from the linter
+  ([#598](https://github.com/fortran-lang/vscode-fortran-support/issues/598))
+
 ## [3.2.0]
 
 ### Added

src/features/linter-provider.ts

@@ -101,7 +101,8 @@ export class FortranLintingProvider {
         compilerOutput += data;
       });
       childProcess.stderr.on('end', () => {
-        const diagnostics = this.getLinterResults(compilerOutput);
+        let diagnostics = this.getLinterResults(compilerOutput);
+        diagnostics = [...new Map(diagnostics.map(v => [JSON.stringify(v), v])).values()];
         this.diagnosticCollection.set(textDocument.uri, diagnostics);
       });
       childProcess.on('error', err => {