Don't use hunk mode for added or deleted files

When entering staging (or patch building) for an added or deleted file, it
doesn't make sense to use hunk mode, because pressing space would stage/unstage
the entire file, and if the user wanted to do that, they would have pressed
space in the Files panel. So always use line mode for added/deleted files by
default, even if the useHunkModeInStagingView user config is on.

pkg/commands/patch/patch.go

@@ -186,3 +186,17 @@ func (self *Patch) AdjustLineNumber(lineNumber int) int {
 
 	return adjustedLineNumber
 }
+
+func (self *Patch) IsSingleHunkForWholeFile() bool {
+	if len(self.hunks) != 1 {
+		return false
+	}
+
+	// We consider a patch to be a single hunk for the whole file if it has only additions or
+	// deletions but not both, and no context lines. This not quite correct, because it will also
+	// return true for a block of added or deleted lines if the diff context size is 0, but in this
+	// case you wouldn't be able to stage things anyway, so it doesn't matter.
+	bodyLines := self.hunks[0].bodyLines
+	return nLinesWithKind(bodyLines, []PatchLineKind{DELETION, CONTEXT}) == 0 ||
+		nLinesWithKind(bodyLines, []PatchLineKind{ADDITION, CONTEXT}) == 0
+}

pkg/commands/patch/patch_test.go

@@ -710,3 +710,64 @@ func TestAdjustLineNumber(t *testing.T) {
 		})
 	}
 }
+
+func TestIsSingleHunkForWholeFile(t *testing.T) {
+	scenarios := []struct {
+		testName       string
+		patchStr       string
+		expectedResult bool
+	}{
+		{
+			testName:       "simpleDiff",
+			patchStr:       simpleDiff,
+			expectedResult: false,
+		},
+		{
+			testName:       "addNewlineToEndOfFile",
+			patchStr:       addNewlineToEndOfFile,
+			expectedResult: false,
+		},
+		{
+			testName:       "removeNewlinefromEndOfFile",
+			patchStr:       removeNewlinefromEndOfFile,
+			expectedResult: false,
+		},
+		{
+			testName:       "twoHunks",
+			patchStr:       twoHunks,
+			expectedResult: false,
+		},
+		{
+			testName:       "twoChangesInOneHunk",
+			patchStr:       twoChangesInOneHunk,
+			expectedResult: false,
+		},
+		{
+			testName:       "newFile",
+			patchStr:       newFile,
+			expectedResult: true,
+		},
+		{
+			testName:       "deletedFile",
+			patchStr:       deletedFile,
+			expectedResult: true,
+		},
+		{
+			testName:       "addNewlineToPreviouslyEmptyFile",
+			patchStr:       addNewlineToPreviouslyEmptyFile,
+			expectedResult: true,
+		},
+		{
+			testName:       "exampleHunk",
+			patchStr:       exampleHunk,
+			expectedResult: false,
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.testName, func(t *testing.T) {
+			patch := Parse(s.patchStr)
+			assert.Equal(t, s.expectedResult, patch.IsSingleHunkForWholeFile())
+		})
+	}
+}

pkg/gui/patch_exploring/state.go

@@ -67,7 +67,7 @@ func NewState(diff string, selectedLineIdx int, view *gocui.View, oldState *Stat
 	}
 
 	selectMode := LINE
-	if useHunkModeByDefault {
+	if useHunkModeByDefault && !patch.IsSingleHunkForWholeFile() {
 		selectMode = HUNK
 	}