stub out basic markdown headings document symbol provider (#33)

to restore default markdown Outline for remapped standard .md documents, and build a custom Evidence markdown Outline for markdown documents navigation in VS Code

src/extension.ts

@@ -1,5 +1,6 @@
 import {
-  commands,
+  languages,
+  window,
   workspace,
   ExtensionContext,
 } from 'vscode';
@@ -10,6 +11,8 @@ import { updateProjectContext } from './config';
 import { statusBar } from './statusBar';
 import { closeTerminal } from './terminal';
 
+import { MarkdownSymbolProvider } from './providers/markdownSymbolProvider';
+
 /**
  * Activates Evidence vscode extension.
  *
@@ -19,6 +22,11 @@ export async function activate(context: ExtensionContext) {
   setExtensionContext(context);
   registerCommands(context);
 
+  // register markdown symbol provider
+  const markdownLanguage = { language: 'emd', scheme: 'file' };
+  const provider = new MarkdownSymbolProvider();
+  languages.registerDocumentSymbolProvider(markdownLanguage, provider);
+
   // check for evidence app files
   const evidenceFiles = await workspace.findFiles('**/.evidence/**/*.*');
   if (workspace.workspaceFolders && evidenceFiles.length > 0) {

src/providers/markdownSymbolProvider.ts

@@ -0,0 +1,38 @@
+import {
+  CancellationToken,
+  DocumentSymbolProvider,
+  Location,
+  ProviderResult,
+  SymbolInformation,
+  SymbolKind,
+  TextDocument,
+} from 'vscode';
+
+/**
+ * Implements custom Evidence markdown document symbol provider.
+ */
+export class MarkdownSymbolProvider implements DocumentSymbolProvider {
+
+  provideDocumentSymbols(document: TextDocument, token: CancellationToken):
+    ProviderResult<SymbolInformation[]> {
+
+    // parse text document symbols per line
+    const symbols: SymbolInformation[] = [];
+    for (let i = 0; i < document.lineCount; i++) {
+      const line = document.lineAt(i);
+
+      // match heading lines
+      const match = line.text.match(/^#+\s+(.*)$/);
+      if (match) {
+        const symbol = new SymbolInformation(match[1], SymbolKind.String,
+          '', // container name
+          new Location(document.uri, line.range)
+        );
+
+        symbols.push(symbol);
+      }
+    }
+
+    return symbols;
+  }
+}