refactor ext_buffer, avoid magic variable names

Author: bobzhang

jscomp/bsb/bsb_ninja_rule.ml

@@ -135,15 +135,15 @@ let make_custom_rules
     if read_cmi then 
       Ext_buffer.add_string buf " -bs-read-cmi";
     if is_dev then 
-      Ext_buffer.add_string buf " $g_dev_incls";      
-    Ext_buffer.add_string buf " $g_lib_incls" ;
+      Ext_buffer.add_ninja_prefix_var buf Bsb_ninja_global_vars.g_dev_incls;      
+    Ext_buffer.add_ninja_prefix_var buf Bsb_build_schemas.g_lib_incls;
     if is_dev then
-      Ext_buffer.add_string buf " $g_dpkg_incls";
+      Ext_buffer.add_ninja_prefix_var buf Bsb_ninja_global_vars.g_dpkg_incls;
     if not has_builtin then   
       Ext_buffer.add_string buf " -nostdlib";
     Ext_buffer.add_string buf " $warnings $bsc_flags";
     if has_gentype then
-      Ext_buffer.add_string buf " $gentypeconfig";
+      Ext_buffer.add_ninja_prefix_var buf Bsb_ninja_global_vars.gentypeconfig;
     Ext_buffer.add_string buf " -o $out $in";
     if postbuild then
       Ext_buffer.add_string buf " $postbuild";
@@ -159,15 +159,15 @@ let make_custom_rules
       Ext_buffer.add_string buf (Ext_filename.maybe_quote x);
     );
     if has_pp then
-      Ext_buffer.add_string buf " $pp_flags";
+      Ext_buffer.add_ninja_prefix_var buf Bsb_ninja_global_vars.pp_flags;
     (match has_reason_react_jsx, reason_react_jsx with
      | false, _ 
      | _, None -> ()
      | _, Some Jsx_v3 
        -> Ext_buffer.add_string buf " -bs-jsx 3"
     );
     if has_ppx then 
-      Ext_buffer.add_string buf " $ppx_flags"; 
+      Ext_buffer.add_ninja_prefix_var buf Bsb_ninja_global_vars.ppx_flags; 
     Ext_buffer.add_string buf " $bsc_flags -o $out -bs-syntax-only -bs-binary-ast $in";   
     Ext_buffer.contents buf
   in  

jscomp/ext/ext_buffer.ml

@@ -121,6 +121,19 @@ let add_char_string b c s  =
   Ext_bytes.unsafe_blit_string s 0 b_buffer (b_position + 1) s_len;
   b.position <- new_position
 
+(* equivalent to add_char " "; add_char "$"; add_string s  *)
+let add_ninja_prefix_var b s =  
+  let s_len = String.length s in
+  let len = s_len + 2 in 
+  let new_position = b.position + len in
+  if new_position > b.length then resize b len;
+  let b_buffer = b.buffer in 
+  let b_position = b.position in 
+  Bytes.unsafe_set b_buffer b_position ' ' ; 
+  Bytes.unsafe_set b_buffer (b_position + 1) '$' ; 
+  Ext_bytes.unsafe_blit_string s 0 b_buffer (b_position + 2) s_len;
+  b.position <- new_position
+
 
 (* let add_bytes b s = add_string b (Bytes.unsafe_to_string s)
 

jscomp/ext/ext_buffer.mli

@@ -108,7 +108,13 @@ val add_string_char :
    string ->
    char -> 
    unit
-
+   
+val add_ninja_prefix_var : 
+   t -> 
+   string -> 
+   unit 
+   
+   
 val add_char_string :    
    t -> 
    char ->