From bac4f0ac1ad317586997bbf412e153900d411e8f Mon Sep 17 00:00:00 2001
From: Andrey Nering <andreynering@users.noreply.github.com>
Date: Wed, 11 Jun 2025 15:44:08 -0300
Subject: [PATCH] fix(diffview): fix behavior of tabs and add tab width setting

---
 internal/exp/diffview/diffview.go             | 18 ++++++++++++++++
 internal/exp/diffview/diffview_test.go        | 21 +++++++++++++++++++
 .../testdata/TestDiffViewTabs/Split.golden    | 15 +++++++++++++
 .../testdata/TestDiffViewTabs/Unified.golden  | 16 ++++++++++++++
 internal/exp/diffview/testdata/TestTabs.after | 15 +++++++++++++
 .../exp/diffview/testdata/TestTabs.before     | 13 ++++++++++++
 6 files changed, 98 insertions(+)
 create mode 100644 internal/exp/diffview/testdata/TestDiffViewTabs/Split.golden
 create mode 100644 internal/exp/diffview/testdata/TestDiffViewTabs/Unified.golden
 create mode 100644 internal/exp/diffview/testdata/TestTabs.after
 create mode 100644 internal/exp/diffview/testdata/TestTabs.before

diff --git a/internal/exp/diffview/diffview.go b/internal/exp/diffview/diffview.go
index 41212b340c1a94bb188c374d9b989e14c708875a..6d2947bca534eb2ccc8466d6483ed6e5d3d48fe8 100644
--- a/internal/exp/diffview/diffview.go
+++ b/internal/exp/diffview/diffview.go
@@ -42,6 +42,7 @@ type DiffView struct {
 	xOffset      int
 	yOffset      int
 	style        Style
+	tabWidth     int
 
 	isComputed bool
 	err        error
@@ -63,6 +64,7 @@ func New() *DiffView {
 		layout:       layoutUnified,
 		contextLines: udiff.DefaultContextLines,
 		lineNumbers:  true,
+		tabWidth:     8,
 	}
 	if lipgloss.HasDarkBackground(os.Stdin, os.Stdout) {
 		dv.style = DefaultDarkStyle
@@ -144,8 +146,16 @@ func (dv *DiffView) YOffset(yOffset int) *DiffView {
 	return dv
 }
 
+// TabWidth sets the tab width. Only relevant for code that contains tabs, like
+// Go code.
+func (dv *DiffView) TabWidth(tabWidth int) *DiffView {
+	dv.tabWidth = tabWidth
+	return dv
+}
+
 // String returns the string representation of the DiffView.
 func (dv *DiffView) String() string {
+	dv.replaceTabs()
 	if err := dv.computeDiff(); err != nil {
 		return err.Error()
 	}
@@ -177,6 +187,14 @@ func (dv *DiffView) String() string {
 	}
 }
 
+// replaceTabs replaces tabs in the before and after file contents with spaces
+// according to the specified tab width.
+func (dv *DiffView) replaceTabs() {
+	spaces := strings.Repeat(" ", dv.tabWidth)
+	dv.before.content = strings.ReplaceAll(dv.before.content, "\t", spaces)
+	dv.after.content = strings.ReplaceAll(dv.after.content, "\t", spaces)
+}
+
 // computeDiff computes the differences between the "before" and "after" files.
 func (dv *DiffView) computeDiff() error {
 	if dv.isComputed {
diff --git a/internal/exp/diffview/diffview_test.go b/internal/exp/diffview/diffview_test.go
index d9f55892024ef4a9da00b0f5586e3f50135e27d9..4feb40a68c140d75a143ed37535573fb05d9fbdd 100644
--- a/internal/exp/diffview/diffview_test.go
+++ b/internal/exp/diffview/diffview_test.go
@@ -29,6 +29,12 @@ var TestNarrowBefore string
 //go:embed testdata/TestNarrow.after
 var TestNarrowAfter string
 
+//go:embed testdata/TestTabs.before
+var TestTabsBefore string
+
+//go:embed testdata/TestTabs.after
+var TestTabsAfter string
+
 type (
 	TestFunc  func(dv *diffview.DiffView) *diffview.DiffView
 	TestFuncs map[string]TestFunc
@@ -137,6 +143,21 @@ func TestDiffView(t *testing.T) {
 	}
 }
 
+func TestDiffViewTabs(t *testing.T) {
+	for layoutName, layoutFunc := range LayoutFuncs {
+		t.Run(layoutName, func(t *testing.T) {
+			dv := diffview.New().
+				Before("main.go", TestTabsBefore).
+				After("main.go", TestTabsAfter).
+				Style(diffview.DefaultLightStyle)
+			dv = layoutFunc(dv)
+
+			output := dv.String()
+			golden.RequireEqual(t, []byte(output))
+		})
+	}
+}
+
 func TestDiffViewWidth(t *testing.T) {
 	for layoutName, layoutFunc := range LayoutFuncs {
 		t.Run(layoutName, func(t *testing.T) {
diff --git a/internal/exp/diffview/testdata/TestDiffViewTabs/Split.golden b/internal/exp/diffview/testdata/TestDiffViewTabs/Split.golden
new file mode 100644
index 0000000000000000000000000000000000000000..47ec287f0894851ff20b75d5f267e9733e30b497
--- /dev/null
+++ b/internal/exp/diffview/testdata/TestDiffViewTabs/Split.golden
@@ -0,0 +1,15 @@
+  …   @@ -2,6 +2,7 @@                                       …                                                       
+  2                                                         2                                                       
+  3   import (                                              3   import (                                            
+  4           "fmt"                                         4           "fmt"                                       
+                                                            5 +         "strings"                                   
+  5   )                                                     6   )                                                   
+  6                                                         7                                                       
+  7   func main() {                                         8   func main() {                                       
+  …   @@ -9,5 +10,6 @@                                      …                                                       
+  9   }                                                    10   }                                                   
+ 10                                                        11                                                       
+ 11   func getContent() string {                           12   func getContent() string {                          
+ 12 -         return "Hello, world!"                       13 +         content := strings.ToUpper("Hello, World!") 
+                                                           14 +         return content                              
+ 13   }                                                    15   }                                                   
\ No newline at end of file
diff --git a/internal/exp/diffview/testdata/TestDiffViewTabs/Unified.golden b/internal/exp/diffview/testdata/TestDiffViewTabs/Unified.golden
new file mode 100644
index 0000000000000000000000000000000000000000..1f71e8a1bfad8219360784d1ef2893d2a86f3b41
--- /dev/null
+++ b/internal/exp/diffview/testdata/TestDiffViewTabs/Unified.golden
@@ -0,0 +1,16 @@
+  …   …   @@ -2,6 +2,7 @@                                     
+  2   2                                                       
+  3   3   import (                                            
+  4   4           "fmt"                                       
+      5 +         "strings"                                   
+  5   6   )                                                   
+  6   7                                                       
+  7   8   func main() {                                       
+  …   …   @@ -9,5 +10,6 @@                                    
+  9  10   }                                                   
+ 10  11                                                       
+ 11  12   func getContent() string {                          
+ 12     -         return "Hello, world!"                      
+     13 +         content := strings.ToUpper("Hello, World!") 
+     14 +         return content                              
+ 13  15   }                                                   
\ No newline at end of file
diff --git a/internal/exp/diffview/testdata/TestTabs.after b/internal/exp/diffview/testdata/TestTabs.after
new file mode 100644
index 0000000000000000000000000000000000000000..26b88f61224561d442b23473ce6b9daaf761aee9
--- /dev/null
+++ b/internal/exp/diffview/testdata/TestTabs.after
@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	fmt.Println(getContent())
+}
+
+func getContent() string {
+	content := strings.ToUpper("Hello, World!")
+	return content
+}
diff --git a/internal/exp/diffview/testdata/TestTabs.before b/internal/exp/diffview/testdata/TestTabs.before
new file mode 100644
index 0000000000000000000000000000000000000000..72d7ebc2699bfd859311b85e3193e6c87013672f
--- /dev/null
+++ b/internal/exp/diffview/testdata/TestTabs.before
@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(getContent())
+}
+
+func getContent() string {
+	return "Hello, world!"
+}