internal/lsp: add a regtest for formatting one-line files

Issue golang/go#36824 complained about
legal go code (e.g., 'package a; func f() {}') that was mishandled
(by being rewritten just as 'package a'). This bug seems to have been
partially fixed, as certified by the new regtests. The comment on
OneLineImports36824 says that the bug would be fixed if gopls
formatted the file before fixing the imports, but it doesn't.

Change-Id: If27fa738e54d9434d5b2f17ed4e52d555cb7c499
Reviewed-on: https://go-review.googlesource.com/c/tools/+/229303
Run-TryBot: Peter Weinberger <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Rebecca Stambler <[email protected]>

Author: pjweinbgo

internal/lsp/regtest/formatting_test.go

@@ -33,6 +33,56 @@ func TestFormatting(t *testing.T) {
 	})
 }
 
+// this is the fixed case from #36824
+const onelineProgram = `
+-- a.go --
+package main; func f() {}
+
+-- a.go.formatted --
+package main
+
+func f() {}
+`
+
+func TestFormattingOneLine36824(t *testing.T) {
+	runner.Run(t, onelineProgram, func(t *testing.T, env *Env) {
+		env.OpenFile("a.go")
+		env.FormatBuffer("a.go")
+		got := env.E.BufferText("a.go")
+		want := env.ReadWorkspaceFile("a.go.formatted")
+		if got != want {
+			t.Errorf("got\n%q wanted\n%q", got, want)
+		}
+	})
+}
+
+const onelineProgramA = `
+-- a.go --
+package x; func f() {fmt.Println()}
+
+-- a.go.imported --
+package x
+
+import "fmt"
+
+func f() { fmt.Println() }
+`
+
+// this is the example from #36824 done properly
+// but gopls does not reformat before fixing the imports
+func TestFormattingOneLineImports36824(t *testing.T) {
+	runner.Run(t, onelineProgramA, func(t *testing.T, env *Env) {
+		env.OpenFile("a.go")
+		env.FormatBuffer("a.go")
+		env.OrganizeImports("a.go")
+		got := env.E.BufferText("a.go")
+		want := env.ReadWorkspaceFile("a.go.imported")
+		if got != want {
+			t.Errorf("OneLineImports go\n%q wanted\n%q", got, want)
+		}
+	})
+}
+
 const disorganizedProgram = `
 -- main.go --
 package main