Allow DiffContextSize to be decreased to zero (#4050)

- **PR Description**

Per #4012, the diff context size should be able to be decreased to zero.
I update the type def for DiffContextSize to be an unsigned integer and
add saturated add and subtraction in `context_lines_controller.go` where
the variable is updated (++ or --)

- **Please check if the PR fulfills these requirements**

* [x] Cheatsheets are up-to-date (run `go generate ./...`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [x] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [x] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

<!--
Be sure to name your PR with an imperative e.g. 'Add worktrees view'
see https://github.com/jesseduffield/lazygit/releases/tag/v0.40.0 for
examples
-->

pkg/commands/git_commands/commit_test.go

@@ -230,7 +230,7 @@ func TestCommitShowCmdObj(t *testing.T) {
 	type scenario struct {
 		testName            string
 		filterPath          string
-		contextSize         int
+		contextSize         uint64
 		similarityThreshold int
 		ignoreWhitespace    bool
 		extDiffCmd          string

pkg/commands/git_commands/stash_test.go

@@ -100,7 +100,7 @@ func TestStashStashEntryCmdObj(t *testing.T) {
 	type scenario struct {
 		testName            string
 		index               int
-		contextSize         int
+		contextSize         uint64
 		similarityThreshold int
 		ignoreWhitespace    bool
 		expected            []string

pkg/commands/git_commands/working_tree_test.go

@@ -210,7 +210,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 		plain               bool
 		cached              bool
 		ignoreWhitespace    bool
-		contextSize         int
+		contextSize         uint64
 		similarityThreshold int
 		runner              *oscommands.FakeCmdObjRunner
 	}
@@ -352,7 +352,7 @@ func TestWorkingTreeShowFileDiff(t *testing.T) {
 		reverse          bool
 		plain            bool
 		ignoreWhitespace bool
-		contextSize      int
+		contextSize      uint64
 		runner           *oscommands.FakeCmdObjRunner
 	}
 

pkg/config/app_config.go

@@ -457,7 +457,7 @@ type AppState struct {
 
 	HideCommandLog             bool
 	IgnoreWhitespaceInDiffView bool
-	DiffContextSize            int
+	DiffContextSize            uint64
 	RenameSimilarityThreshold  int
 	LocalBranchSortOrder       string
 	RemoteBranchSortOrder      string

pkg/gui/controllers/context_lines_controller.go

@@ -3,6 +3,7 @@ package controllers
 import (
 	"errors"
 	"fmt"
+	"math"
 
 	"github.com/jesseduffield/lazygit/pkg/gui/context"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
@@ -68,7 +69,9 @@ func (self *ContextLinesController) Increase() error {
 			return err
 		}
 
-		self.c.AppState.DiffContextSize++
+		if self.c.AppState.DiffContextSize < math.MaxUint64 {
+			self.c.AppState.DiffContextSize++
+		}
 		return self.applyChange()
 	}
 
@@ -76,14 +79,14 @@ func (self *ContextLinesController) Increase() error {
 }
 
 func (self *ContextLinesController) Decrease() error {
-	old_size := self.c.AppState.DiffContextSize
+	if self.isShowingDiff() {
-
-	if self.isShowingDiff() && old_size > 1 {
 		if err := self.checkCanChangeContext(); err != nil {
 			return err
 		}
 
-		self.c.AppState.DiffContextSize = old_size - 1
+		if self.c.AppState.DiffContextSize > 0 {
+			self.c.AppState.DiffContextSize--
+		}
 		return self.applyChange()
 	}
 

pkg/integration/tests/staging/diff_context_change.go

@@ -127,6 +127,26 @@ var DiffContextChange = NewIntegrationTest(NewIntegrationTestArgs{
 				Contains(`+3b`),
 				Contains(` 4a`),
 			).
+			Press(keys.Universal.DecreaseContextInDiffView).
+			Tap(func() {
+				t.ExpectToast(Equals("Changed diff context size to 0"))
+			}).
+			SelectedLines(
+				Contains(`@@ -3,1 +3 @@`),
+				Contains(`-3a`),
+				Contains(`+3b`),
+			).
+			Press(keys.Universal.IncreaseContextInDiffView).
+			Tap(func() {
+				t.ExpectToast(Equals("Changed diff context size to 1"))
+			}).
+			SelectedLines(
+				Contains(`@@ -2,3 +2,3 @@`),
+				Contains(` 2a`),
+				Contains(`-3a`),
+				Contains(`+3b`),
+				Contains(` 4a`),
+			).
 			Press(keys.Universal.IncreaseContextInDiffView).
 			Tap(func() {
 				t.ExpectToast(Equals("Changed diff context size to 2"))