Cleanup bytecode generator (pegjs/pegjs#450): Replace PUSH opcode wit…

…h PUSH_EMPTY_STRING opcode because it only used with empty strings
peggyjs · May 20, 2021 · aa44ec3 · aa44ec3
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -48,6 +48,18 @@ Released: TBD
 
   Now bytecode generation pass is independent from the JavaScript backend.
   [@Mingun](https://github.com/peggyjs/peggy/pull/117)
+- Some opcodes from `compiler/opcode.js` is deprecated. Although you shouldn't use
+  them directly because they are notconsidered as a public API, some plugins use them.
+  For that reason backward compatibility is preserved:
+  - Opcode `MATCH_REGEXP` is deprecated and replaced by `MATCH_CHAR_CLASS` with the same value.
+  - Added new opcode `PUSH_EMPTY_STRING` that put on stack new empty string
+  - Opcode `PUSH` is deprecated because it was used only for pushing empty string constants
+    and they now pushed with `PUSH_EMPTY_STRING`
+
+  Instead of relying on the library opcodes it is better to have a copy of them,
+  especially if your plugin replaces both `generateBytecode` as `generateJs` passes.
+
+  [@Mingun](https://github.com/peggyjs/peggy/pull/117)
 
 ### Bug fixes
 

diff --git a/lib/compiler/opcodes.js b/lib/compiler/opcodes.js
@@ -4,61 +4,64 @@
 const opcodes = {
   // Stack Manipulation
 
-  PUSH:             0,    // PUSH c
-  PUSH_UNDEFINED:   1,    // PUSH_UNDEFINED
-  PUSH_NULL:        2,    // PUSH_NULL
-  PUSH_FAILED:      3,    // PUSH_FAILED
-  PUSH_EMPTY_ARRAY: 4,    // PUSH_EMPTY_ARRAY
-  PUSH_CURR_POS:    5,    // PUSH_CURR_POS
-  POP:              6,    // POP
-  POP_CURR_POS:     7,    // POP_CURR_POS
-  POP_N:            8,    // POP_N n
-  NIP:              9,    // NIP
-  APPEND:           10,   // APPEND
-  WRAP:             11,   // WRAP n
-  TEXT:             12,   // TEXT
-  PLUCK:            36,   // PLUCK n, k, p1, ..., pK
+  /** @deprecated Unused */
+  PUSH:              0,    // PUSH c
+  PUSH_EMPTY_STRING: 35,   // PUSH_EMPTY_STRING
+  PUSH_UNDEFINED:    1,    // PUSH_UNDEFINED
+  PUSH_NULL:         2,    // PUSH_NULL
+  PUSH_FAILED:       3,    // PUSH_FAILED
+  PUSH_EMPTY_ARRAY:  4,    // PUSH_EMPTY_ARRAY
+  PUSH_CURR_POS:     5,    // PUSH_CURR_POS
+  POP:               6,    // POP
+  POP_CURR_POS:      7,    // POP_CURR_POS
+  POP_N:             8,    // POP_N n
+  NIP:               9,    // NIP
+  APPEND:            10,   // APPEND
+  WRAP:              11,   // WRAP n
+  TEXT:              12,   // TEXT
+  PLUCK:             36,   // PLUCK n, k, p1, ..., pK
 
   // Conditions and Loops
 
-  IF:               13,   // IF t, f
-  IF_ERROR:         14,   // IF_ERROR t, f
-  IF_NOT_ERROR:     15,   // IF_NOT_ERROR t, f
-  WHILE_NOT_ERROR:  16,   // WHILE_NOT_ERROR b
+  IF:                13,   // IF t, f
+  IF_ERROR:          14,   // IF_ERROR t, f
+  IF_NOT_ERROR:      15,   // IF_NOT_ERROR t, f
+  WHILE_NOT_ERROR:   16,   // WHILE_NOT_ERROR b
 
   // Matching
 
-  MATCH_ANY:        17,   // MATCH_ANY a, f, ...
-  MATCH_STRING:     18,   // MATCH_STRING s, a, f, ...
-  MATCH_STRING_IC:  19,   // MATCH_STRING_IC s, a, f, ...
-  MATCH_CHAR_CLASS: 20,   // MATCH_CHAR_CLASS c, a, f, ...
+  MATCH_ANY:        17,    // MATCH_ANY a, f, ...
+  MATCH_STRING:     18,    // MATCH_STRING s, a, f, ...
+  MATCH_STRING_IC:  19,    // MATCH_STRING_IC s, a, f, ...
+  MATCH_CHAR_CLASS: 20,    // MATCH_CHAR_CLASS c, a, f, ...
   /** @deprecated Replaced with `MATCH_CHAR_CLASS` */
-  MATCH_REGEXP:     20,   // MATCH_REGEXP r, a, f, ...
-  ACCEPT_N:         21,   // ACCEPT_N n
-  ACCEPT_STRING:    22,   // ACCEPT_STRING s
-  FAIL:             23,   // FAIL e
+  MATCH_REGEXP:     20,    // MATCH_REGEXP r, a, f, ...
+  ACCEPT_N:         21,    // ACCEPT_N n
+  ACCEPT_STRING:    22,    // ACCEPT_STRING s
+  FAIL:             23,    // FAIL e
 
   // Calls
 
-  LOAD_SAVED_POS:   24,   // LOAD_SAVED_POS p
-  UPDATE_SAVED_POS: 25,   // UPDATE_SAVED_POS
-  CALL:             26,   // CALL f, n, pc, p1, p2, ..., pN
+  LOAD_SAVED_POS:    24,   // LOAD_SAVED_POS p
+  UPDATE_SAVED_POS:  25,   // UPDATE_SAVED_POS
+  CALL:              26,   // CALL f, n, pc, p1, p2, ..., pN
 
   // Rules
 
-  RULE:             27,   // RULE r
+  RULE:              27,   // RULE r
 
   // Failure Reporting
 
-  SILENT_FAILS_ON:  28,   // SILENT_FAILS_ON
-  SILENT_FAILS_OFF: 29    // SILENT_FAILS_OFF
+  SILENT_FAILS_ON:   28,   // SILENT_FAILS_ON
+  SILENT_FAILS_OFF:  29    // SILENT_FAILS_OFF
 
   // Because the tests have hard-coded opcode numbers, don't renumber
   // existing opcodes.  New opcodes that have been put in the correct
   // sections above are repeated here in order to ensure we don't
   // reuse them.
   //
-  // 30-35 reserved for @mingun
+  // 30-34 reserved for @mingun
+  // PUSH_EMPTY_STRING: 35
   // PLUCK: 36
 };
 

diff --git a/lib/compiler/passes/generate-bytecode.js b/lib/compiler/passes/generate-bytecode.js
@@ -12,9 +12,9 @@ const visitor = require("../visitor");
 // Stack Manipulation
 // ------------------
 //
-//  [0] PUSH c
+//  [35] PUSH_EMPTY_STRING
 //
-//        stack.push(literals[c]);
+//        stack.push("");
 //
 //  [1] PUSH_UNDEFINED
 //
@@ -614,11 +614,9 @@ function generateBytecode(ast) {
             : [op.ACCEPT_STRING, stringIndex],
           [op.FAIL, expectedIndex]
         );
-      } else {
-        const stringIndex = addLiteralConst("");
-
-        return [op.PUSH, stringIndex];
       }
+
+      return [op.PUSH_EMPTY_STRING];
     },
 
     class(node) {

diff --git a/lib/compiler/passes/generate-js.js b/lib/compiler/passes/generate-js.js
@@ -339,9 +339,9 @@ function generateJS(ast, options) {
 
       while (ip < end) {
         switch (bc[ip]) {
-          case op.PUSH:               // PUSH c
-            parts.push(stack.push(l(bc[ip + 1])));
-            ip += 2;
+          case op.PUSH_EMPTY_STRING:  // PUSH_EMPTY_STRING
+            parts.push(stack.push("''"));
+            ip++;
             break;
 
           case op.PUSH_CURR_POS:      // PUSH_CURR_POS

diff --git a/test/unit/compiler/passes/generate-bytecode.spec.js b/test/unit/compiler/passes/generate-bytecode.spec.js
@@ -628,12 +628,12 @@ describe("compiler pass |generateBytecode|", function() {
 
       it("generates correct bytecode", function() {
         expect(pass).to.changeAST(grammar, bytecodeDetails([
-          0, 0   // PUSH
+          35     // PUSH_EMPTY_STRING
         ]));
       });
 
       it("defines correct constants", function() {
-        expect(pass).to.changeAST(grammar, constsDetails([""], [], [], []));
+        expect(pass).to.changeAST(grammar, constsDetails([], [], [], []));
       });
     });