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Fix a bug with named NEVER_MATCH expressions #454

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Fix a bug with named NEVER_MATCH expressions #454

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34085af
Fix named NEVER_MATCH
Dec 12, 2023
2742d1e
Build Artifacts
Dec 12, 2023
390fc54
Add a CHANGELOG entry
Dec 12, 2023
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ Released: TBD

### Minor Changes

- [#454](https://github.com/peggyjs/peggy/pull/454) Fix a bug with named NEVER_MATCH expressions
- [#453](https://github.com/peggyjs/peggy/pull/453) Make generate-bytecode.js ts-clean
- [#452](https://github.com/peggyjs/peggy/pull/452) Fixes to prepare generate-bytecode.js for ts-check
- [#432](https://github.com/peggyjs/peggy/pull/432) Add peggy.code-workspace
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2 changes: 1 addition & 1 deletion docs/js/benchmark-bundle.min.js
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3 changes: 0 additions & 3 deletions docs/js/examples.js
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Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,6 @@ function peg$parse(input, options) {
var peg$e11 = peg$literalExpectation(" ", false);
var peg$e12 = peg$literalExpectation("c", false);
var peg$e13 = peg$classExpectation([["a", "c"]], false, false);
var peg$e14 = peg$otherExpectation("The rest of the input");

var peg$f0 = function(match, rest) { return {match, rest}; };
var peg$f1 = function(match, rest) { return {match, rest}; };
Expand Down Expand Up @@ -1488,8 +1487,6 @@ function peg$parse(input, options) {
}
s0 = input.substring(s0, peg$currPos);
peg$silentFails--;
s1 = peg$FAILED;
if (peg$silentFails === 0) { peg$fail(peg$e14); }

return s0;
}
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2 changes: 1 addition & 1 deletion docs/js/test-bundle.min.js
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2 changes: 1 addition & 1 deletion docs/vendor/peggy/peggy.min.js
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6 changes: 3 additions & 3 deletions lib/compiler/passes/generate-bytecode.js
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Expand Up @@ -715,8 +715,8 @@ function generateBytecode(ast, options) {

named(node, context) {
const match = node.match || 0;
// Expectation not required if node always fail
const nameIndex = (match === NEVER_MATCH)
// Expectation not required if node always match
const nameIndex = (match === ALWAYS_MATCH)
? -1
: addExpectedConst({ type: "rule", value: node.name });

Expand All @@ -728,7 +728,7 @@ function generateBytecode(ast, options) {
[op.SILENT_FAILS_ON],
generate(node.expression, context),
[op.SILENT_FAILS_OFF],
buildCondition(match, [op.IF_ERROR], [op.FAIL, nameIndex], [])
buildCondition(-match, [op.IF_ERROR], [op.FAIL, nameIndex], [])
);
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@Mingun Mingun Dec 12, 2023 •
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Good catch! The bug probably was introduced during rebase while adapt initial PR to the new code after another merged PR.

Actually, the whole buildSequence could be replaced by [op.FAIL, nameIndex] if node always fail and there are no actions or semantic predicates (because they can have side effects), but anyway, it is better to do in a separate pass.

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if node always fail and there are no actions or semantic predicates (because they can have side effects)

There are already comments about adding side-effect analysis so we can do that kind of thing...

},

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4 changes: 2 additions & 2 deletions test/behavior/generated-parser-behavior.spec.js
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Expand Up @@ -215,11 +215,11 @@ describe("generated parser behavior", () => {
});
});

it("reports match failure and doesn't records any expectations when expression never match", () => {
it("reports match failure and records an expectation of type \"other\" when expression never match", () => {
const parser = peg.generate("start 'start' = []", options);

expect(parser).to.failToParse("b", {
expected: [],
expected: [{ type:"other", description: "start" }],
});
});

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