Refactor repo_paths.go to use git rev-parse

This changes GetRepoPaths() to pull information from `git rev-parse`
instead of effectively reimplementing git's logic for pathfinding. This
change fixes issues with bare repos, esp. versioned homedir use cases,
by aligning lazygit's path handling to what git itself does.

This change also enables lazygit to run from arbitrary subdirectories of
a repository, including correct handling of symlinks, including "deep"
symlinks into a repo, worktree, a repo's submodules, etc.

Integration tests are now resilient against unintended side effects from
the host's environment variables. Of necessity, $PATH and $TERM are the
only env vars allowed through now.

pkg/integration/tests/worktree/double_nested_linked_submodule.go

@@ -0,0 +1,93 @@
+package worktree
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+// Even though this involves submodules, it's a worktree test since
+// it's really exercising lazygit's ability to correctly do pathfinding
+// in a complex use case.
+var DoubleNestedLinkedSubmodule = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Open lazygit in a link to a repo's double nested submodules",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(config *config.AppConfig) {
+		config.UserConfig.Gui.ShowFileTree = false
+	},
+	SetupRepo: func(shell *Shell) {
+		// we're going to have a directory structure like this:
+		// project
+		//  - repo/outerSubmodule/innerSubmodule/a/b/c
+		//  - link (symlink to repo/outerSubmodule/innerSubmodule/a/b/c)
+		//
+		shell.CreateFileAndAdd("rootFile", "rootStuff")
+		shell.Commit("initial repo commit")
+
+		shell.Chdir("..")
+		shell.CreateDir("innerSubmodule")
+		shell.Chdir("innerSubmodule")
+		shell.Init()
+		shell.CreateFileAndAdd("a/b/c/blah", "blah\n")
+		shell.Commit("initial inner commit")
+
+		shell.Chdir("..")
+		shell.CreateDir("outerSubmodule")
+		shell.Chdir("outerSubmodule")
+		shell.Init()
+		shell.CreateFileAndAdd("foo", "foo")
+		shell.Commit("initial outer commit")
+		// the git config (-c) parameter below is required
+		// to let git create a file-protocol/path submodule
+		shell.RunCommand([]string{"git", "-c", "protocol.file.allow=always", "submodule", "add", "../innerSubmodule"})
+		shell.Commit("add dependency as innerSubmodule")
+
+		shell.Chdir("../repo")
+		shell.RunCommand([]string{"git", "-c", "protocol.file.allow=always", "submodule", "add", "../outerSubmodule"})
+		shell.Commit("add dependency as outerSubmodule")
+		shell.Chdir("outerSubmodule")
+		shell.RunCommand([]string{"git", "-c", "protocol.file.allow=always", "submodule", "update", "--init", "--recursive"})
+
+		shell.Chdir("innerSubmodule")
+		shell.UpdateFile("a/b/c/blah", "updated content\n")
+
+		shell.Chdir("../../..")
+		shell.RunCommand([]string{"ln", "-s", "repo/outerSubmodule/innerSubmodule/a/b/c", "link"})
+
+		shell.Chdir("link")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Branches().
+			Lines(
+				Contains("HEAD detached"),
+				Contains("master"),
+			)
+
+		t.Views().Commits().
+			Lines(
+				Contains("initial inner commit"),
+			)
+
+		t.Views().Files().
+			IsFocused().
+			Lines(
+				Contains(" M a/b/c/blah"), // shows as modified
+			).
+			PressPrimaryAction().
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			Title(Equals("Commit summary")).
+			Type("Update blah").
+			Confirm()
+
+		t.Views().Files().
+			IsEmpty()
+
+		t.Views().Commits().
+			Lines(
+				Contains("Update blah"),
+				Contains("initial inner commit"),
+			)
+	},
+})