Pass --filename to shfmt when available

This will aid in language dialect detection.

server/src/shfmt/__tests__/index.test.ts

@@ -58,7 +58,7 @@ describe('formatter', () => {
     expect(async () => {
       await getFormattingResult({ document: FIXTURE_DOCUMENT.PARSE_PROBLEMS })
     }).rejects.toThrow(
-      'Shfmt: exited with status 1: <standard input>:10:1: > must be followed by a word',
+      /Shfmt: exited with status 1: .*\/testing\/fixtures\/parse-problems.sh:10:1: > must be followed by a word/,
     )
   })
 
@@ -584,4 +584,22 @@ describe('formatter', () => {
       ]
     `)
   })
+
+  it('should omit filename from the shfmt comment when it cannot be determined', async () => {
+    // There's no easy way to see what filename has been passed to shfmt without inspecting the
+    // contents of the logs. As a workaround, we set a non-file:// URI on a dodgy document to
+    // trigger an exception and inspect the error message.
+    const testDocument = TextDocument.create(
+      'http://localhost/',
+      'shellscript',
+      0,
+      FIXTURE_DOCUMENT.PARSE_PROBLEMS.getText(),
+    )
+
+    expect(async () => {
+      await getFormattingResult({ document: testDocument })
+    }).rejects.toThrow(
+      /Shfmt: exited with status 1: <standard input>:10:1: > must be followed by a word/,
+    )
+  })
 })

server/src/shfmt/index.ts

@@ -41,9 +41,7 @@ export class Formatter {
     formatOptions?: LSP.FormattingOptions | null,
     shfmtConfig?: Record<string, string | boolean> | null,
   ): Promise<TextEdit[]> {
-    const documentText = document.getText()
-
-    const result = await this.runShfmt(documentText, formatOptions, shfmtConfig)
+    const result = await this.runShfmt(document, formatOptions, shfmtConfig)
 
     if (!this._canFormat) {
       return []
@@ -61,7 +59,7 @@ export class Formatter {
   }
 
   private async runShfmt(
-    documentText: string,
+    document: TextDocument,
     formatOptions?: LSP.FormattingOptions | null,
     shfmtConfig?: Record<string, string | boolean> | null,
   ): Promise<string> {
@@ -74,6 +72,12 @@ export class Formatter {
     if (shfmtConfig?.simplifyCode) args.push('-s') // --simplify
     if (shfmtConfig?.spaceRedirects) args.push('-sr') // --space-redirects
 
+    // If we can determine a local filename, pass that to shfmt to aid language dialect detection
+    const filePathMatch = document.uri.match(/^file:\/\/(.*)$/)
+    if (filePathMatch) {
+      args.push(`--filename=${filePathMatch[1]}`)
+    }
+
     logger.debug(`Shfmt: running "${this.executablePath} ${args.join(' ')}"`)
 
     let out = ''
@@ -90,7 +94,7 @@ export class Formatter {
         // This is solved in Node >= 15.1 by the "on('spawn', ...)" event, but we need to
         // support earlier versions.
       })
-      proc.stdin.end(documentText)
+      proc.stdin.end(document.getText())
     })
 
     let exit