fix: command re-running caused early line truncating

internal/ui/reload_test.go

@@ -0,0 +1,114 @@
+package ui
+
+import (
+	"testing"
+	"time"
+
+	"github.com/chenasraf/watchr/internal/runner"
+)
+
+func waitDone(t *testing.T, m *model) {
+	t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		if m.streamResult != nil && m.streamResult.IsDone() {
+			// fire one tick after done so model state syncs
+			_, _ = m.Update(streamTickMsg(time.Now()))
+			return
+		}
+		_, _ = m.Update(streamTickMsg(time.Now()))
+		time.Sleep(10 * time.Millisecond)
+	}
+	t.Fatal("stream did not complete")
+}
+
+// TestReload_SameLineCountUpdatesInPlace verifies that when the new run
+// produces the same number of lines as the previous run, the new content
+// (delivered via in-place updates) is reflected in m.lines.
+func TestReload_SameLineCountUpdatesInPlace(t *testing.T) {
+	cfg := Config{Command: "echo new1; echo new2; echo new3", Shell: "sh"}
+	m := testModel(cfg)
+	m.height = 30
+	m.width = 80
+
+	// Pretend a previous run left 3 lines of stale content
+	m.lines = []runner.Line{
+		{Number: 1, Content: "old1"},
+		{Number: 2, Content: "old2"},
+		{Number: 3, Content: "old3"},
+	}
+	m.lastLineCount = 3
+	m.updateFiltered()
+
+	_, _ = m.actionReload()
+	waitDone(t, m)
+
+	if len(m.lines) != 3 {
+		t.Fatalf("expected 3 lines, got %d", len(m.lines))
+	}
+	for i, want := range []string{"new1", "new2", "new3"} {
+		if m.lines[i].Content != want {
+			t.Errorf("line %d: expected %q, got %q", i, want, m.lines[i].Content)
+		}
+	}
+}
+
+// TestReload_FewerLinesTrimsToNewRun verifies that when the new run produces
+// fewer lines than the previous run, m.lines is trimmed AND shows the new
+// content in the surviving slots (not stale prev content).
+func TestReload_FewerLinesTrimsToNewRun(t *testing.T) {
+	cfg := Config{Command: "echo new1; echo new2", Shell: "sh"}
+	m := testModel(cfg)
+	m.height = 30
+	m.width = 80
+
+	m.lines = []runner.Line{
+		{Number: 1, Content: "old1"},
+		{Number: 2, Content: "old2"},
+		{Number: 3, Content: "old3"},
+		{Number: 4, Content: "old4"},
+	}
+	m.lastLineCount = 4
+	m.updateFiltered()
+
+	_, _ = m.actionReload()
+	waitDone(t, m)
+
+	if len(m.lines) != 2 {
+		t.Fatalf("expected 2 lines after reload, got %d", len(m.lines))
+	}
+	for i, want := range []string{"new1", "new2"} {
+		if m.lines[i].Content != want {
+			t.Errorf("line %d: expected %q, got %q", i, want, m.lines[i].Content)
+		}
+	}
+}
+
+// TestReload_MoreLines verifies that when the new run produces more lines
+// than the previous run, all new lines are visible.
+func TestReload_MoreLines(t *testing.T) {
+	cfg := Config{Command: "echo a; echo b; echo c; echo d; echo e", Shell: "sh"}
+	m := testModel(cfg)
+	m.height = 30
+	m.width = 80
+
+	m.lines = []runner.Line{
+		{Number: 1, Content: "old1"},
+		{Number: 2, Content: "old2"},
+		{Number: 3, Content: "old3"},
+	}
+	m.lastLineCount = 3
+	m.updateFiltered()
+
+	_, _ = m.actionReload()
+	waitDone(t, m)
+
+	if len(m.lines) != 5 {
+		t.Fatalf("expected 5 lines, got %d", len(m.lines))
+	}
+	for i, want := range []string{"a", "b", "c", "d", "e"} {
+		if m.lines[i].Content != want {
+			t.Errorf("line %d: expected %q, got %q", i, want, m.lines[i].Content)
+		}
+	}
+}

internal/ui/update.go

@@ -70,7 +70,9 @@ func (m *model) startStreaming() tea.Cmd {
 	m.streamResult = m.runner.RunStreaming(m.ctx, m.lines)
 	m.streaming = true
 	m.loading = true
-	m.lastLineCount = len(m.lines)
+	// lastLineCount tracks the streamResult's CurrentLineCount (lines produced
+	// by the current run), which starts at 0 for a fresh streaming result.
+	m.lastLineCount = 0
 	m.exitCode = -1
 	m.errorMsg = ""
 	m.userScrolled = false
@@ -116,16 +118,23 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			return m, nil
 		}
 
-		// Check for new lines
-		newLines := m.streamResult.GetLines()
-		newCount := len(newLines)
+		isDone := m.streamResult.IsDone()
+		currentCount := m.streamResult.GetCurrentLineCount()
 
-		if newCount != m.lastLineCount {
+		// Sync m.lines whenever the stream has produced new line writes since
+		// the last tick (in-place edits and appends both bump CurrentLineCount),
+		// or once on completion so the trim-to-currentCount path runs.
+		if currentCount != m.lastLineCount || isDone {
+			newLines := m.streamResult.GetLines()
+			// On completion, drop any leftover slots that the new run never
+			// wrote into — they still hold previous-run content.
+			if isDone && currentCount < len(newLines) {
+				newLines = newLines[:currentCount]
+			}
 			m.lines = newLines
-			m.lastLineCount = newCount
+			m.lastLineCount = currentCount
 			m.updateFiltered()
 
-			// Auto-scroll to bottom if user hasn't manually scrolled
 			if !m.userScrolled {
 				visible := m.visibleLines()
 				if visible > 0 {
@@ -135,8 +144,7 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			}
 		}
 
-		// Check if command completed
-		if m.streamResult.IsDone() {
+		if isDone {
 			m.streaming = false
 			m.loading = false
 			m.exitCode = m.streamResult.ExitCode
@@ -144,13 +152,6 @@ func (m *model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				m.errorMsg = m.streamResult.Error.Error()
 			}
 
-			// Trim excess lines from previous run
-			currentCount := m.streamResult.GetCurrentLineCount()
-			if currentCount < len(m.lines) {
-				m.lines = m.lines[:currentCount]
-				m.updateFiltered()
-			}
-
 			// If auto-refresh is enabled and timer starts from end, schedule the next run
 			if m.config.RefreshInterval > 0 && !m.config.RefreshFromStart {
 				m.refreshStartTime = time.Now()