Implement capture_stderr C-API option

As an embeddable library we should try to play nice with
our parents resources. It is therefore desirable to have
a way to capture messages on stderr. This makes it easier
and safer to use libsass in eg. threaded environments.

Core errors (mainly memory allocation problems) and
dev/debug data is still printed to stderr directly.

Author: mgreter

docs/api-context-internal.md

@@ -51,6 +51,10 @@ struct Sass_Options : Sass_Output_Options {
   // Treat source_string as sass (as opposed to scss)
   bool is_indented_syntax_src;
 
+  // If this options is set, nothing will be printed to stderr anymore
+  // The aggregated output on stderr can be fetched via stderr_string
+  bool suppress_stderr;
+
   // The input path is used for source map
   // generation. It can be used to define
   // something with string compilation or to
@@ -105,6 +109,9 @@ struct Sass_Context : Sass_Options
   // generated output data
   char* output_string;
 
+  // messages on stderr
+  char* stderr_string;
+
   // generated source map json
   char* source_map_string;
 

docs/api-context.md

@@ -46,6 +46,11 @@ bool omit_source_map_url;
 bool is_indented_syntax_src;
 ```
 ```C
+// If this options is set, nothing will be printed to stderr anymore
+// The aggregated output on stderr can be fetched via stderr_string
+bool suppress_stderr;
+```
+```C
 // The input path is used for source map
 // generating. It can be used to define
 // something with string compilation or to
@@ -111,6 +116,10 @@ enum Sass_Input_Style type;
 char* output_string;
 ```
 ```C
+// messages on stderr
+char* stderr_string;
+```
+```C
 // generated source map json
 char* source_map_string;
 ```
@@ -197,6 +206,7 @@ void sass_data_context_set_options (struct Sass_Data_Context* data_ctx, struct S
 
 // Getters for Sass_Context values
 const char* sass_context_get_output_string (struct Sass_Context* ctx);
+const char* sass_context_get_stderr_string (struct Sass_Context* ctx);
 int sass_context_get_error_status (struct Sass_Context* ctx);
 const char* sass_context_get_error_json (struct Sass_Context* ctx);
 const char* sass_context_get_error_text (struct Sass_Context* ctx);
@@ -262,6 +272,7 @@ void sass_option_set_source_map_contents (struct Sass_Options* options, bool sou
 void sass_option_set_source_map_file_urls (struct Sass_Options* options, bool source_map_file_urls);
 void sass_option_set_omit_source_map_url (struct Sass_Options* options, bool omit_source_map_url);
 void sass_option_set_is_indented_syntax_src (struct Sass_Options* options, bool is_indented_syntax_src);
+void sass_option_set_suppress_stderr (struct Sass_Options* options, bool suppress_stderr);
 void sass_option_set_indent (struct Sass_Options* options, const char* indent);
 void sass_option_set_linefeed (struct Sass_Options* options, const char* linefeed);
 void sass_option_set_input_path (struct Sass_Options* options, const char* input_path);

include/sass/context.h

@@ -96,6 +96,7 @@ ADDAPI void ADDCALL sass_option_set_source_map_contents (struct Sass_Options* op
 ADDAPI void ADDCALL sass_option_set_source_map_file_urls (struct Sass_Options* options, bool source_map_file_urls);
 ADDAPI void ADDCALL sass_option_set_omit_source_map_url (struct Sass_Options* options, bool omit_source_map_url);
 ADDAPI void ADDCALL sass_option_set_is_indented_syntax_src (struct Sass_Options* options, bool is_indented_syntax_src);
+ADDAPI void ADDCALL sass_option_set_suppress_stderr (struct Sass_Options* options, bool suppress_stderr);
 ADDAPI void ADDCALL sass_option_set_indent (struct Sass_Options* options, const char* indent);
 ADDAPI void ADDCALL sass_option_set_linefeed (struct Sass_Options* options, const char* linefeed);
 ADDAPI void ADDCALL sass_option_set_input_path (struct Sass_Options* options, const char* input_path);
@@ -111,6 +112,7 @@ ADDAPI void ADDCALL sass_option_set_c_functions (struct Sass_Options* options, S
 
 // Getters for Sass_Context values
 ADDAPI const char* ADDCALL sass_context_get_output_string (struct Sass_Context* ctx);
+ADDAPI const char* ADDCALL sass_context_get_stderr_string (struct Sass_Context* ctx);
 ADDAPI int ADDCALL sass_context_get_error_status (struct Sass_Context* ctx);
 ADDAPI const char* ADDCALL sass_context_get_error_json (struct Sass_Context* ctx);
 ADDAPI const char* ADDCALL sass_context_get_error_text (struct Sass_Context* ctx);

src/bind.cpp

@@ -11,7 +11,7 @@
 
 namespace Sass {
 
-  void bind(std::string type, std::string name, Parameters_Obj ps, Arguments_Obj as, Env* env, Eval* eval, Backtraces& traces)
+  void bind(std::string type, std::string name, Parameters_Obj ps, Arguments_Obj as, Context* ctx, Env* env, Eval* eval, Backtraces& traces)
   {
     std::string callee(type + " " + name);
 
@@ -194,7 +194,9 @@ namespace Sass {
             msg << (LP == 1 ? " argument" : " arguments");
             msg << " but " << arg_count;
             msg << (arg_count == 1 ? " was passed" : " were passed.");
-            deprecated_bind(msg.str(), as->pstate());
+            // ToDo: we only need ctx here to capture the message on stderr
+            // ToDo: once deprecation is gone, remove it from method args
+            ctx->print_stderr(deprecated_bind(msg.str(), as->pstate()));
 
             while (arglist->length() > LP - ip) {
               arglist->elements().erase(arglist->elements().end() - 1);

src/bind.hpp

@@ -8,7 +8,7 @@
 
 namespace Sass {
 
-  void bind(std::string type, std::string name, Parameters_Obj, Arguments_Obj, Env*, Eval*, Backtraces& traces);
+  void bind(std::string type, std::string name, Parameters_Obj, Arguments_Obj, Context* ctx, Env*, Eval*, Backtraces& traces);
 
 }
 

src/context.cpp

@@ -76,6 +76,8 @@ namespace Sass {
     head_imports(0),
     plugins(),
     emitter(c_options),
+    CERR(std::cerr),
+    STDERR(),
 
     ast_gc(),
     strings(),
@@ -142,6 +144,14 @@ namespace Sass {
     sort (c_importers.begin(), c_importers.end(), sort_importers);
   }
 
+  void Context::print_stderr(const std::string& msg)
+  {
+    STDERR << msg;
+    if (!c_options.suppress_stderr) {
+      CERR << msg;
+    }
+  }
+
   Context::~Context()
   {
     // resources were allocated by malloc

src/context.hpp

@@ -2,6 +2,7 @@
 #define SASS_CONTEXT_H
 
 #include <string>
+#include <sstream>
 #include <vector>
 #include <map>
 
@@ -44,6 +45,9 @@ namespace Sass {
     Plugins plugins;
     Output emitter;
 
+    std::ostream& CERR;
+    std::ostringstream STDERR;
+
     // generic ast node garbage container
     // used to avoid possible circular refs
     CallStack ast_gc;
@@ -104,6 +108,8 @@ namespace Sass {
     Sass_Output_Style output_style() { return c_options.output_style; };
     std::vector<std::string> get_included_files(bool skip = false, size_t headers = 0);
 
+    void print_stderr(const std::string& msg);
+
   private:
     void collect_plugin_paths(const char* paths_str);
     void collect_plugin_paths(string_list* paths_array);

src/error_handling.cpp

@@ -134,66 +134,77 @@ namespace Sass {
 
   }
 
-
-  void warn(std::string msg, ParserState pstate)
+  std::string warn(std::string msg, ParserState pstate)
   {
-    std::cerr << "Warning: " << msg << std::endl;
+    std::ostringstream sstrm;
+    sstrm << "Warning: " << msg << std::endl;
+    return sstrm.str();
   }
 
-  void warning(std::string msg, ParserState pstate)
+  std::string warning(std::string msg, ParserState pstate)
   {
     std::string cwd(Sass::File::get_cwd());
     std::string abs_path(Sass::File::rel2abs(pstate.path, cwd, cwd));
     std::string rel_path(Sass::File::abs2rel(pstate.path, cwd, cwd));
     std::string output_path(Sass::File::path_for_console(rel_path, abs_path, pstate.path));
 
-    std::cerr << "WARNING on line " << pstate.line+1 << ", column " << pstate.column+1 << " of " << output_path << ":" << std::endl;
-    std::cerr << msg << std::endl << std::endl;
+    std::ostringstream sstrm;
+    sstrm << "WARNING on line " << pstate.line + 1;
+    sstrm << ", column " << pstate.column + 1;
+    sstrm << " of " << output_path << std::endl;
+    sstrm << msg << std::endl;
+    sstrm << std::endl;
+    return sstrm.str();
   }
 
-  void warn(std::string msg, ParserState pstate, Backtrace* bt)
+  std::string warn(std::string msg, ParserState pstate, Backtrace* bt)
   {
-    warn(msg, pstate);
+    return warn(msg, pstate);
   }
 
-  void deprecated_function(std::string msg, ParserState pstate)
+  std::string deprecated_function(std::string msg, ParserState pstate)
   {
     std::string cwd(Sass::File::get_cwd());
     std::string abs_path(Sass::File::rel2abs(pstate.path, cwd, cwd));
     std::string rel_path(Sass::File::abs2rel(pstate.path, cwd, cwd));
     std::string output_path(Sass::File::path_for_console(rel_path, abs_path, pstate.path));
 
-    std::cerr << "DEPRECATION WARNING: " << msg << std::endl;
-    std::cerr << "will be an error in future versions of Sass." << std::endl;
-    std::cerr << "        on line " << pstate.line+1 << " of " << output_path << std::endl;
+    std::ostringstream sstrm;
+    sstrm << "DEPRECATION WARNING: " << msg << std::endl;
+    sstrm << "will be an error in future versions of Sass." << std::endl;
+    sstrm << "        on line " << pstate.line+1 << " of " << output_path << std::endl;
+    return sstrm.str();
   }
 
-  void deprecated(std::string msg, std::string msg2, bool with_column, ParserState pstate)
+  std::string deprecated(std::string msg, std::string msg2, bool with_column, ParserState pstate)
   {
     std::string cwd(Sass::File::get_cwd());
     std::string abs_path(Sass::File::rel2abs(pstate.path, cwd, cwd));
     std::string rel_path(Sass::File::abs2rel(pstate.path, cwd, cwd));
     std::string output_path(Sass::File::path_for_console(rel_path, pstate.path, pstate.path));
 
-    std::cerr << "DEPRECATION WARNING on line " << pstate.line + 1;
-    if (with_column) std::cerr << ", column " << pstate.column + pstate.offset.column + 1;
-    if (output_path.length()) std::cerr << " of " << output_path;
-    std::cerr << ":" << std::endl;
-    std::cerr << msg << std::endl;
-    if (msg2.length()) std::cerr << msg2 << std::endl;
-    std::cerr << std::endl;
+    std::ostringstream sstrm;
+    sstrm << "DEPRECATION WARNING on line " << pstate.line + 1;
+    if (output_path.length()) sstrm << " of " << output_path;
+    sstrm << ":" << std::endl;
+    sstrm << msg << " and will be an error in future versions of Sass." << std::endl;
+    if (msg2.length()) sstrm << msg2 << std::endl;
+    sstrm << std::endl;
+    return sstrm.str();
   }
 
-  void deprecated_bind(std::string msg, ParserState pstate)
+  std::string deprecated_bind(std::string msg, ParserState pstate)
   {
     std::string cwd(Sass::File::get_cwd());
     std::string abs_path(Sass::File::rel2abs(pstate.path, cwd, cwd));
     std::string rel_path(Sass::File::abs2rel(pstate.path, cwd, cwd));
     std::string output_path(Sass::File::path_for_console(rel_path, abs_path, pstate.path));
 
-    std::cerr << "WARNING: " << msg << std::endl;
-    std::cerr << "        on line " << pstate.line+1 << " of " << output_path << std::endl;
-    std::cerr << "This will be an error in future versions of Sass." << std::endl;
+    std::ostringstream sstrm;
+    sstrm << "WARNING: " << msg << std::endl;
+    sstrm << "        on line " << pstate.line+1 << " of " << output_path << std::endl;
+    sstrm << "This will be an error in future versions of Sass." << std::endl;
+    return sstrm.str();
   }
 
   // should be replaced with error with backtraces

src/error_handling.hpp

@@ -212,14 +212,13 @@ namespace Sass {
 
   }
 
-  void warn(std::string msg, ParserState pstate);
-  void warn(std::string msg, ParserState pstate, Backtrace* bt);
-  void warning(std::string msg, ParserState pstate);
-
-  void deprecated_function(std::string msg, ParserState pstate);
-  void deprecated(std::string msg, std::string msg2, bool with_column, ParserState pstate);
-  void deprecated_bind(std::string msg, ParserState pstate);
-  // void deprecated(std::string msg, ParserState pstate, Backtrace* bt);
+  std::string warn(std::string msg, ParserState pstate);
+  std::string warn(std::string msg, ParserState pstate, Backtrace* bt);
+  std::string warning(std::string msg, ParserState pstate);
+
+  std::string deprecated_function(std::string msg, ParserState pstate);
+  std::string deprecated(std::string msg, std::string msg2, bool with_column, ParserState pstate);
+  std::string deprecated_bind(std::string msg, ParserState pstate);
 
   void coreError(std::string msg, ParserState pstate);
   void error(std::string msg, ParserState pstate, Backtraces& traces);

src/eval.cpp

@@ -389,9 +389,11 @@ namespace Sass {
 
     std::string result(unquote(message->to_sass()));
     std::cerr << "WARNING: " << result << std::endl;
+    std::ostringstream sstrm;
     traces.push_back(Backtrace(w->pstate()));
-    std::cerr << traces_to_string(traces, "         ");
-    std::cerr << std::endl;
+    sstrm << traces_to_string(traces, "         ");
+    sstrm << std::endl;
+    ctx.print_stderr(sstrm.str());
     options().output_style = outstyle;
     traces.pop_back();
     return 0;
@@ -485,8 +487,11 @@ namespace Sass {
     std::string output_path(Sass::File::path_for_console(rel_path, abs_path, d->pstate().path));
     options().output_style = outstyle;
 
-    std::cerr << output_path << ":" << d->pstate().line+1 << " DEBUG: " << result;
-    std::cerr << std::endl;
+    std::ostringstream sstrm;
+    sstrm << output_path << ":" << d->pstate().line+1 << " DEBUG: " << result;
+    sstrm << std::endl;
+    ctx.print_stderr(sstrm.str());
+
     return 0;
   }
 
@@ -1048,7 +1053,7 @@ namespace Sass {
     env_stack().push_back(&fn_env);
 
     if (func || body) {
-      bind(std::string("Function"), c->name(), params, args, &fn_env, this, traces);
+      bind(std::string("Function"), c->name(), params, args, &ctx, &fn_env, this, traces);
       std::string msg(", in function `" + c->name() + "`");
       traces.push_back(Backtrace(c->pstate(), msg));
       callee_stack().push_back({
@@ -1088,7 +1093,7 @@ namespace Sass {
 
       // populates env with default values for params
       std::string ff(c->name());
-      bind(std::string("Function"), c->name(), params, args, &fn_env, this, traces);
+      bind(std::string("Function"), c->name(), params, args, &ctx, &fn_env, this, traces);
       std::string msg(", in function `" + c->name() + "`");
       traces.push_back(Backtrace(c->pstate(), msg));
       callee_stack().push_back({