Use embedded syntax files if no --syntax option has been provided.

This allows one to run re2c/re2go/re2rust without --syntax option and
get the same behaviour as before.

src/codegen/syntax.cc

@@ -4,6 +4,10 @@
 #include "src/codegen/output.h"
 #include "src/codegen/syntax.h"
 
+extern const char* DEFAULT_SYNTAX_C;
+extern const char* DEFAULT_SYNTAX_GO;
+extern const char* DEFAULT_SYNTAX_RUST;
+
 namespace re2c {
 
 Stx::Stx(OutAllocator& alc)
@@ -334,33 +338,52 @@ StxFile::~StxFile() {
     if (file) fclose(file);
 }
 
-Ret StxFile::read() {
+Ret StxFile::read(Lang lang) {
     msg.filenames.push_back(fname);
 
-    file = fopen(fname.c_str(), "rb");
-    if (!file) RET_FAIL(error("cannot open syntax file '%s'", fname.c_str()));
-
-    // get file size
-    fseek(file, 0, SEEK_END);
-    flen = static_cast<size_t>(ftell(file));
-    fseek(file, 0, SEEK_SET);
-
-    // allocate buffer
-    buf = new uint8_t[flen + 1];
-
-    // read file contents into buffer and append terminating zero at the end
-    if (fread(buf, 1, flen, file) != flen) {
-        RET_FAIL(error("cannot read syntax file '%s'", fname.c_str()));
+    if (fname.empty()) {
+        // use the default syntax config that is provided as a string
+        const char* src = nullptr;
+        switch (lang) {
+            case Lang::C: src = DEFAULT_SYNTAX_C; break;
+            case Lang::GO: src = DEFAULT_SYNTAX_GO; break;
+            case Lang::RUST: src = DEFAULT_SYNTAX_RUST; break;
+        }
+        flen = strlen(src);
+
+        // allocate buffer
+        buf = new uint8_t[flen + 1];
+
+        // fill in buffer from the config string
+        memcpy(buf, src, flen);
+        buf[flen] = 0;
+    } else {
+        // use the provided syntax file
+        file = fopen(fname.c_str(), "rb");
+        if (!file) RET_FAIL(error("cannot open syntax file '%s'", fname.c_str()));
+
+        // get file size
+        fseek(file, 0, SEEK_END);
+        flen = static_cast<size_t>(ftell(file));
+        fseek(file, 0, SEEK_SET);
+
+        // allocate buffer
+        buf = new uint8_t[flen + 1];
+
+        // read file contents into buffer and append terminating zero at the end
+        if (fread(buf, 1, flen, file) != flen) {
+            RET_FAIL(error("cannot read syntax file '%s'", fname.c_str()));
+        }
+        buf[flen] = 0;
     }
-    buf[flen] = 0;
 
     cur = tok = pos = buf;
     return Ret::OK;
 }
 
-Ret load_syntax_config(const std::string& fname, Msg& msg, OutAllocator& alc, Stx& stx) {
+Ret load_syntax_config(const std::string& fname, Msg& msg, OutAllocator& alc, Stx& stx, Lang lang) {
     StxFile sf(fname, msg, alc);
-    CHECK_RET(sf.read());
+    CHECK_RET(sf.read(lang));
     CHECK_RET(sf.parse(stx));
     return Ret::OK;
 }

src/codegen/syntax.h

@@ -171,7 +171,7 @@ class StxFile {
   public:
     StxFile(const std::string& fname, Msg& msg, OutAllocator& alc);
     ~StxFile();
-    Ret read();
+    Ret read(Lang lang);
     Ret parse(Stx& stx);
     int lex_token(YYSTYPE* yylval);
     bool check_conf_name(const char* name) const;
@@ -277,13 +277,13 @@ inline StxCode* Stx::make_code_list(
     return x;
 }
 
-Ret load_syntax_config(const std::string& fname, Msg& msg, OutAllocator& alc, Stx& stx);
-
 loc_t StxFile::tok_loc() const {
     DCHECK(pos <= tok);
     return {loc.line, static_cast<uint32_t>(tok - pos), loc.file};
 }
 
+Ret load_syntax_config(const std::string& fname, Msg& msg, OutAllocator& alc, Stx& stx, Lang lang);
+
 } // namespace re2c
 
 #endif // _RE2C_CODEGEN_SYNTAX_

src/main.cc

@@ -146,7 +146,7 @@ LOCAL_NODISCARD(Ret compile(int, char* argv[])) {
 
     // Load syntax file before opening source files, as it must have file index 0.
     Stx stx(out_alc);
-    CHECK_RET(load_syntax_config(globopts.syntax_file, msg, out_alc, stx));
+    CHECK_RET(load_syntax_config(globopts.syntax_file, msg, out_alc, stx, globopts.lang));
 
     Input input(&globopts, msg);
     CHECK_RET(input.open(globopts.source_file, nullptr));