[lldb] Fix output of help format

lldb/source/Interpreter/CommandInterpreter.cpp

@@ -3182,26 +3182,41 @@ void CommandInterpreter::OutputHelpText(Stream &strm, llvm::StringRef word_text,
 
   uint32_t chars_left = max_columns;
 
-  auto nextWordLength = [](llvm::StringRef S) {
-    size_t pos = S.find(' ');
-    return pos == llvm::StringRef::npos ? S.size() : pos;
+  auto start_new_line = [&] {
+    strm.EOL();
+    strm.Indent();
+    chars_left = max_columns - indent_size;
   };
 
   while (!text.empty()) {
-    if (text.front() == '\n' ||
-        (text.front() == ' ' && nextWordLength(text.ltrim(' ')) > chars_left)) {
-      strm.EOL();
-      strm.Indent();
-      chars_left = max_columns - indent_size;
-      if (text.front() == '\n')
-        text = text.drop_front();
-      else
-        text = text.ltrim(' ');
-    } else {
-      strm.PutChar(text.front());
-      --chars_left;
+    if (text.starts_with('\n')) {
       text = text.drop_front();
+      start_new_line();
+      continue;
     }
+
+    // Calculate the size of the next fragment. A fragment is defined as zero
+    // or more spaces followed by a word (which is sequence of non-whitespace
+    // characters). It is assumed that the only possible whitespaces in the
+    // input text are ' ' and '\n'.
+    size_t word_start_pos = text.find_first_not_of(' ');
+    size_t word_end_pos = text.find_first_of(" \n", /*from=*/word_start_pos);
+    size_t fragment_size =
+        word_end_pos == llvm::StringRef::npos ? text.size() : word_end_pos;
+
+    if (fragment_size > chars_left && text.starts_with(' ')) {
+      // The fragment does not fit on the current line, but begins with a space.
+      // Break the line at the beginning of the word contained in the fragment.
+      text = text.drop_front(word_start_pos);
+      start_new_line();
+      continue;
+    }
+
+    // Print out the fragment. It fits on the current line or does not contain
+    // spaces where we could break the line.
+    strm.PutCString(text.take_front(fragment_size));
+    text = text.drop_front(fragment_size);
+    chars_left = fragment_size > chars_left ? 0 : chars_left - fragment_size;
   }
 
   strm.EOL();

lldb/test/API/commands/help/TestHelp.py

@@ -239,7 +239,7 @@ def test_help_unknown_flag(self):
     def test_help_format_output(self):
         """Test that help output reaches TerminalWidth and wraps to the next
         line if needed."""
-        self.runCmd("settings set term-width 118")
+        self.runCmd("settings set term-width 105")
         self.expect(
             "help format",
             matching=True,
@@ -249,9 +249,9 @@ def test_help_format_output(self):
             ],
         )
 
-        # The length of the first line will not be exactly 108 because we split
+        # The length of the first line will not be exactly 105 because we split
         # at the last whitespace point before the limit.
-        self.runCmd("settings set term-width 108")
+        self.runCmd("settings set term-width 104")
         self.expect(
             "help format",
             matching=True,
@@ -271,6 +271,16 @@ def test_help_format_output(self):
             ],
         )
 
+        # Check that line splitting works with newline characters too. The raw
+        # input after the word "pointer" does not contain spaces among more than
+        # a hundred subsequent characters, the words are separated by newlines.
+        self.runCmd("settings set term-width 80")
+        self.expect(
+            "help format",
+            matching=True,
+            substrs=["'p' or \"pointer\""],
+        )
+
     @no_debug_info_test
     def test_help_option_group_format_options_usage(self):
         """Test that help on commands that use OptionGroupFormat options provide relevant help specific to that command."""