Add whitespace control options: trim_blocks, lstrip_blocks (#116)

include/inja/config.hpp

@@ -24,6 +24,9 @@ struct LexerConfig {
   std::string comment_close {"#}"};
   std::string open_chars {"#{"};
 
+  bool trim_blocks {false};
+  bool lstrip_blocks {false};
+
   void update_open_chars() {
     open_chars = "";
     if (open_chars.find(line_statement[0]) == std::string::npos) {

include/inja/environment.hpp

@@ -77,6 +77,16 @@ class Environment {
     m_impl->lexer_config.update_open_chars();
   }
 
+  /// Sets whether to remove the first newline after a block
+  void set_trim_blocks(bool trim_blocks) {
+    m_impl->lexer_config.trim_blocks = trim_blocks;
+  }
+
+  /// Sets whether to strip the spaces and tabs from the start of a line to a block
+  void set_lstrip_blocks(bool lstrip_blocks) {
+    m_impl->lexer_config.lstrip_blocks = lstrip_blocks;
+  }
+
   /// Sets the element notation syntax
   void set_element_notation(ElementNotation notation) {
     m_impl->parser_config.notation = notation;

include/inja/lexer.hpp

@@ -59,12 +59,15 @@ class Lexer {
 
         // try to match one of the opening sequences, and get the close
         nonstd::string_view open_str = m_in.substr(m_pos);
+        bool must_lstrip = false;
         if (inja::string_view::starts_with(open_str, m_config.expression_open)) {
           m_state = State::ExpressionStart;
         } else if (inja::string_view::starts_with(open_str, m_config.statement_open)) {
           m_state = State::StatementStart;
+          must_lstrip = m_config.lstrip_blocks;
         } else if (inja::string_view::starts_with(open_str, m_config.comment_open)) {
           m_state = State::CommentStart;
+          must_lstrip = m_config.lstrip_blocks;
         } else if ((m_pos == 0 || m_in[m_pos - 1] == '\n') &&
                    inja::string_view::starts_with(open_str, m_config.line_statement)) {
           m_state = State::LineStart;
@@ -72,8 +75,13 @@ class Lexer {
           m_pos += 1; // wasn't actually an opening sequence
           goto again;
         }
-        if (m_pos == m_tok_start) goto again;  // don't generate empty token
-        return make_token(Token::Kind::Text);
+
+        nonstd::string_view text = string_view::slice(m_in, m_tok_start, m_pos);
+        if (must_lstrip)
+          text = clear_final_line_if_whitespace(text);
+
+        if (text.empty()) goto again;  // don't generate empty token
+        return Token(Token::Kind::Text, text);
       }
       case State::ExpressionStart: {
         m_state = State::ExpressionBody;
@@ -100,7 +108,7 @@ class Lexer {
       case State::LineBody:
         return scan_body("\n", Token::Kind::LineStatementClose);
       case State::StatementBody:
-        return scan_body(m_config.statement_close, Token::Kind::StatementClose);
+        return scan_body(m_config.statement_close, Token::Kind::StatementClose, m_config.trim_blocks);
       case State::CommentBody: {
         // fast-scan to comment close
         size_t end = m_in.substr(m_pos).find(m_config.comment_close);
@@ -111,7 +119,10 @@ class Lexer {
         // return the entire comment in the close token
         m_state = State::Text;
         m_pos += end + m_config.comment_close.size();
-        return make_token(Token::Kind::CommentClose);
+        Token tok = make_token(Token::Kind::CommentClose);
+        if (m_config.trim_blocks)
+          skip_newline();
+        return tok;
       }
     }
   }
@@ -119,7 +130,7 @@ class Lexer {
   const LexerConfig& get_config() const { return m_config; }
 
  private:
-  Token scan_body(nonstd::string_view close, Token::Kind closeKind) {
+  Token scan_body(nonstd::string_view close, Token::Kind closeKind, bool trim = false) {
   again:
     // skip whitespace (except for \n as it might be a close)
     if (m_tok_start >= m_in.size()) return make_token(Token::Kind::Eof);
@@ -133,7 +144,10 @@ class Lexer {
     if (inja::string_view::starts_with(m_in.substr(m_tok_start), close)) {
       m_state = State::Text;
       m_pos = m_tok_start + close.size();
-      return make_token(closeKind);
+      Token tok = make_token(closeKind);
+      if (trim)
+        skip_newline();
+      return tok;
     }
 
     // skip \n
@@ -254,6 +268,34 @@ class Lexer {
   Token make_token(Token::Kind kind) const {
     return Token(kind, string_view::slice(m_in, m_tok_start, m_pos));
   }
+
+  void skip_newline() {
+    if (m_pos < m_in.size()) {
+      char ch = m_in[m_pos];
+      if (ch == '\n')
+        m_pos += 1;
+      else if (ch == '\r') {
+        m_pos += 1;
+        if (m_pos < m_in.size() && m_in[m_pos] == '\n')
+          m_pos += 1;
+      }
+    }
+  }
+
+  static nonstd::string_view clear_final_line_if_whitespace(nonstd::string_view text)
+  {
+    nonstd::string_view result = text;
+    while (!result.empty()) {
+      char ch = result.back();
+      if (ch == ' ' || ch == '\t')
+       result.remove_suffix(1);
+      else if (ch == '\n' || ch == '\r')
+        break;
+      else
+        return text;
+    }
+    return result;
+  }
 };
 
 }