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remarkSyntaxDiagram: fix rendering of (x y z)* #145

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merged 2 commits into from
Jan 20, 2021
Merged

remarkSyntaxDiagram: fix rendering of (x y z)* #145

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f27dab1
remarkSyntaxDiagram: fix rendering of (x y z)*
kennytm Jan 19, 2021
a579fc1
syntaxDiagram: fix comments
kennytm Jan 20, 2021
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121 changes: 99 additions & 22 deletions src/lib/__tests__/remarkSyntaxDiagram.js
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Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,54 @@ describe('deepEq', () => {
})
})

describe('isRTLCapable', () => {
it('treats leaf nodes as RTL capable', () => {
expect(isRTLCapable({ type: 'Terminal', text: 'a' })).toBeTruthy()
expect(isRTLCapable({ type: 'NonTerminal', text: 'a' })).toBeTruthy()
expect(isRTLCapable({ type: 'Skip' })).toBeTruthy()
})
it('treats sequences to be not RTL capable', () => {
expect(isRTLCapable({
type: 'Sequence',
items: [
{ type: 'Terminal', text: 'a' },
{ type: 'Terminal', text: 'b' },
],
})).toBeFalsy();
expect(isRTLCapable({
type: 'OptionalSequence',
items: [
{ type: 'Terminal', text: 'a' },
{ type: 'Terminal', text: 'b' },
],
})).toBeFalsy()
})
it('can see through choices', () => {
expect(isRTLCapable({
type: 'Choice',
normalIndex: 0,
options: [
{ type: 'Terminal', text: 'a' },
{ type: 'Terminal', text: 'b' },
],
})).toBeTruthy()
expect(isRTLCapable({
type: 'Choice',
normalIndex: 0,
options: [
{ type: 'Terminal', text: 'a' },
{
type: 'Sequence',
items: [
{ type: 'Terminal', text: 'a' },
{ type: 'Terminal', text: 'b' },
],
}
],
})).toBeFalsy()
})
})

describe('appendNodeToChoices', () => {
it('can recognize the `a | a? b` pattern', () => {
let opts = [
Expand Down Expand Up @@ -299,14 +347,17 @@ describe('appendNodeToSequence', () => {
{ type: 'Terminal', text: 'a' },
]
appendNodeToSequence(items, {
type: 'OneOrMore',
item: { type: 'Skip' },
repeat: {
type: 'Sequence',
items: [
{ type: 'Terminal', text: ',' },
{ type: 'Terminal', text: 'a' },
],
type: 'Optional',
item: {
type: 'OneOrMore',
item: {
type: 'Sequence',
items: [
{ type: 'Terminal', text: ',' },
{ type: 'Terminal', text: 'a' },
],
},
repeat: { type: 'Skip' },
},
})
expect(items).toEqual([
Expand All @@ -318,36 +369,62 @@ describe('appendNodeToSequence', () => {
},
])
})
it('just appends without special patterns', () => {
it('just appends when repeating part is not RTL capable', () => {
let items = [
{ type: 'Terminal', text: 'x' },
{ type: 'Terminal', text: 'a' },
]
appendNodeToSequence(items, {
type: 'OneOrMore',
item: { type: 'Skip' },
repeat: {
type: 'Sequence',
items: [
{ type: 'Terminal', text: ',' },
{ type: 'Terminal', text: 'b' },
],
const tail = {
type: 'Optional',
item: {
type: 'OneOrMore',
item: {
type: 'Sequence',
items: [
{
type: 'Sequence',
items: [
{ type: 'Terminal', text: 'AND' },
{ type: 'Terminal', text: 'THEN' },
],
},
{ type: 'Terminal', text: 'a' },
],
},
repeat: { type: 'Skip' },
},
})
}
appendNodeToSequence(items, tail)
expect(items).toEqual([
{ type: 'Terminal', text: 'x' },
{ type: 'Terminal', text: 'a' },
{
tail,
])
})
it('just appends without special patterns', () => {
let items = [
{ type: 'Terminal', text: 'x' },
{ type: 'Terminal', text: 'a' },
]
const tail = {
type: 'Optional',
item: {
type: 'OneOrMore',
item: { type: 'Skip' },
repeat: {
item: {
type: 'Sequence',
items: [
{ type: 'Terminal', text: ',' },
{ type: 'Terminal', text: 'b' },
],
},
repeat: { type: 'Skip' },
},
}
appendNodeToSequence(items, tail)
expect(items).toEqual([
{ type: 'Terminal', text: 'x' },
{ type: 'Terminal', text: 'a' },
tail,
])
})
})
Expand Down
52 changes: 42 additions & 10 deletions src/lib/remarkSyntaxDiagram.js
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,9 @@ const ebnfParser = pegjs.generate(`
case '+':
return {type: 'OneOrMore', item: p, repeat: {type: 'Skip'}};
case '*':
return {type: 'OneOrMore', item: {type: 'Skip'}, repeat: p};
return options.context.isRTLCapable(p) ?
{type: 'OneOrMore', item: {type: 'Skip'}, repeat: p} :
{type: 'Optional', item: {type: 'OneOrMore', item: p, repeat: {type: 'Skip'}}};
default:
return p;
}
Expand Down Expand Up @@ -109,6 +111,34 @@ function deepEq(a, b) {
return aa.length === bb.length && aa.every((n, i) => deepEq(n, bb[i]))
}

/**
* Checks whether the component can be read from right to left. This also means
* the component is only one node wide.
*
* @param {RRComponent} a -
* the railroad component
* @returns {boolean} whether the component can be read from right to left
*/
function isRTLCapable(a) {
switch (a.type) {
case 'Skip':
case 'Terminal':
case 'NonTerminal':
return true;
case 'Optional':
return isRTLCapable(a.item);
case 'OneOrMore':
return isRTLCapable(a.item) && isRTLCapable(a.repeat);
case 'Choice':
return a.options.every(isRTLCapable);
case 'Sequence':
case 'OptionalSequence':
case 'Stack':
const length = a.items.length;
return length === 1 ? isRTLCapable(a.items[0]) : length === 0;
}
}

/**
* Appends an EBNF node to a Choice container.
*
Expand Down Expand Up @@ -147,7 +177,8 @@ function appendNodeToChoices(opts, node) {
* Appends an EBNF node to a Sequence container.
*
* This function will also try to optimize the pattern `a (b a)*` into the
* specialized railroad component `OneOrMore(item=a, repeat=b)`.
* specialized railroad component `OneOrMore(item=a, repeat=b)`, if the node
* `b` is capable to be read RTL (e.g. a single terminal, but not a sequence).
*
* @param {RRComponent[]} items -
* a list of existing items, the new node will be appended here
Expand All @@ -156,18 +187,19 @@ function appendNodeToChoices(opts, node) {
*/
function appendNodeToSequence(items, node) {
if (
node.type === 'OneOrMore' &&
node.item.type === 'Skip' &&
node.repeat.type === 'Sequence' &&
node.repeat.items.length === 2
node.type === 'Optional' &&
node.item.type === 'OneOrMore' &&
node.item.repeat.type === 'Skip' &&
node.item.item.type === 'Sequence' &&
node.item.item.items.length === 2
) {
const left = items[items.length - 1]
const right = node.repeat.items[1]
if (deepEq(left, right)) {
const [ repeat, right ] = node.item.item.items;
if (isRTLCapable(repeat) && deepEq(left, right)) {
items[items.length - 1] = {
type: 'OneOrMore',
item: left,
repeat: node.repeat.items[0],
repeat,
}
return
}
Expand Down Expand Up @@ -245,7 +277,7 @@ function remarkSyntaxDiagram(tree) {
try {
/** @type {{name: string, content: RRComponent}[]} */
const grammar = ebnfParser.parse(node.value, {
context: { appendNodeToChoices, appendNodeToSequence },
context: { appendNodeToChoices, appendNodeToSequence, isRTLCapable },
})
const diagrams = grammar
.map(({ name, content }) => {
Expand Down