[lldb] Improve editline completion formatting

lldb/include/lldb/Host/Editline.h

@@ -238,6 +238,8 @@ class Editline {
   /// Convert the current input lines into a UTF8 StringList
   StringList GetInputAsStringList(int line_count = UINT32_MAX);
 
+  size_t GetTerminalWidth() { return m_terminal_width; }
+
 private:
   /// Sets the lowest line number for multi-line editing sessions.  A value of
   /// zero suppresses line number printing in the prompt.

lldb/source/Host/common/Editline.cpp

@@ -927,12 +927,86 @@ unsigned char Editline::BufferEndCommand(int ch) {
 static void
 PrintCompletion(FILE *output_file,
                 llvm::ArrayRef<CompletionResult::Completion> results,
-                size_t max_len) {
+                size_t max_completion_length, size_t max_length) {
+  constexpr size_t ellipsis_length = 3;
+  constexpr size_t padding_length = 8;
+  constexpr size_t separator_length = 4;
+
+  const size_t description_col =
+      std::min(max_completion_length + padding_length, max_length);
+
   for (const CompletionResult::Completion &c : results) {
-    fprintf(output_file, "\t%-*s", (int)max_len, c.GetCompletion().c_str());
-    if (!c.GetDescription().empty())
-      fprintf(output_file, " -- %s", c.GetDescription().c_str());
-    fprintf(output_file, "\n");
+    if (c.GetCompletion().empty())
+      continue;
+
+    // Print the leading padding.
+    fprintf(output_file, "        ");
+
+    // Print the completion with trailing padding to the description column if
+    // that fits on the screen. Otherwise print whatever fits on the screen
+    // followed by ellipsis.
+    const size_t completion_length = c.GetCompletion().size();
+    if (padding_length + completion_length < max_length) {
+      fprintf(output_file, "%-*s",
+              static_cast<int>(description_col - padding_length),
+              c.GetCompletion().c_str());
+    } else {
+      // If the completion doesn't fit on the screen, print ellipsis and don't
+      // bother with the description.
+      fprintf(output_file, "%.*s...\n\n",
+              static_cast<int>(max_length - padding_length - ellipsis_length),
+              c.GetCompletion().c_str());
+      continue;
+    }
+
+    // If we don't have a description, or we don't have enough space left to
+    // print the separator followed by the ellipsis, we're done.
+    if (c.GetDescription().empty() ||
+        description_col + separator_length + ellipsis_length >= max_length) {
+      fprintf(output_file, "\n");
+      continue;
+    }
+
+    // Print the separator.
+    fprintf(output_file, " -- ");
+
+    // Descriptions can contain newlines. We want to print them below each
+    // other, aligned after the separator. For example, foo has a
+    // two-line description:
+    //
+    // foo   -- Something that fits on the line.
+    //          More information below.
+    //
+    // However, as soon as a line exceed the available screen width and
+    // print ellipsis, we don't print the next line. For example, foo has a
+    // three-line description:
+    //
+    // foo   -- Something that fits on the line.
+    //          Something much longer  that doesn't fit...
+    //
+    // Because we had to print ellipsis on line two, we don't print the
+    // third line.
+    bool first = true;
+    for (llvm::StringRef line : llvm::split(c.GetDescription(), '\n')) {
+      if (line.empty())
+        break;
+      if (!first)
+        fprintf(output_file, "%*s",
+                static_cast<int>(description_col + separator_length), "");
+
+      first = false;
+      const size_t position = description_col + separator_length;
+      const size_t description_length = line.size();
+      if (position + description_length < max_length) {
+        fprintf(output_file, "%.*s\n", static_cast<int>(description_length),
+                line.data());
+      } else {
+        fprintf(output_file, "%.*s...\n",
+                static_cast<int>(max_length - position - ellipsis_length),
+                line.data());
+        continue;
+      }
+    }
   }
 }
 
@@ -953,7 +1027,8 @@ void Editline::DisplayCompletions(
   const size_t max_len = longest->GetCompletion().size();
 
   if (results.size() < page_size) {
-    PrintCompletion(editline.m_output_file, results, max_len);
+    PrintCompletion(editline.m_output_file, results, max_len,
+                    editline.GetTerminalWidth());
     return;
   }
 
@@ -963,7 +1038,7 @@ void Editline::DisplayCompletions(
     size_t next_size = all ? remaining : std::min(page_size, remaining);
 
     PrintCompletion(editline.m_output_file, results.slice(cur_pos, next_size),
-                    max_len);
+                    max_len, editline.GetTerminalWidth());
 
     cur_pos += next_size;
 

lldb/test/API/terminal/TestEditlineCompletions.py

@@ -0,0 +1,64 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+from lldbsuite.test.lldbpexpect import PExpectTest
+
+
+class EditlineCompletionsTest(PExpectTest):
+    @skipIfAsan
+    @skipIfEditlineSupportMissing
+    def test_completion_truncated(self):
+        """Test that the completion is correctly truncated."""
+        self.launch(dimensions=(10, 20))
+        self.child.send("_regexp-\t")
+        self.child.expect("        _regexp-a...")
+        self.child.expect("        _regexp-b...")
+
+    @skipIfAsan
+    @skipIfEditlineSupportMissing
+    def test_description_truncated(self):
+        """Test that the description is correctly truncated."""
+        self.launch(dimensions=(10, 70))
+        self.child.send("_regexp-\t")
+        self.child.expect(
+            "        _regexp-attach    -- Attach to process by ID or name."
+        )
+        self.child.expect(
+            "        _regexp-break     -- Set a breakpoint using one of several..."
+        )
+
+    @skipIfAsan
+    @skipIfEditlineSupportMissing
+    def test_separator_omitted(self):
+        """Test that the separated is correctly omitted."""
+        self.launch(dimensions=(10, 32))
+        self.child.send("_regexp-\t")
+        self.child.expect("        _regexp-attach   \r\n")
+        self.child.expect("        _regexp-break    \r\n")
+
+    @skipIfAsan
+    @skipIfEditlineSupportMissing
+    def test_separator(self):
+        """Test that the separated is correctly printed."""
+        self.launch(dimensions=(10, 33))
+        self.child.send("_regexp-\t")
+        self.child.expect("        _regexp-attach    -- A...")
+        self.child.expect("        _regexp-break     -- S...")
+
+    @skipIfAsan
+    @skipIfEditlineSupportMissing
+    def test_multiline_description(self):
+        """Test that multi-line descriptions are correctly padded and truncated."""
+        self.launch(dimensions=(10, 72))
+        self.child.send("k\t")
+        self.child.expect(
+            "        kdp-remote -- Connect to a process via remote KDP server."
+        )
+        self.child.expect(
+            "                      If no UDP port is specified, port 41139 is assu..."
+        )
+        self.child.expect(
+            "                      kdp-remote is an abbreviation for 'process conn..."
+        )
+        self.child.expect("        kill       -- Terminate the current target process.")