The CoffeeScript language has a good deal of optional syntax, implicit syntax, and shorthand syntax. This can greatly complicate a grammar and bloat the resulting parse table. Instead of making the parser handle it all, we take a series of passes over the token stream, using this Rewriter to convert shorthand into the unambiguous long form, add implicit indentation and parentheses, and generally clean things up.
Create a generated token: one that exists due to a use of implicit syntax.
generate = (tag, value) -> tok = [tag, value] tok.generated = yes tok
class exports.RewriterHelpful snippet for debugging:
console.log (t[0] + '/' + t[1] for t in @tokens).join ' 'Rewrite the token stream in multiple passes, one logical filter at a time. This could certainly be changed into a single pass through the stream, with a big ol' efficient switch, but it's much nicer to work with like this. The order of these passes matters -- indentation must be corrected before implicit parentheses can be wrapped around blocks of code.
rewrite: (@tokens) -> @removeLeadingNewlines() @removeMidExpressionNewlines() @closeOpenCalls() @closeOpenIndexes() @addImplicitIndentation() @tagPostfixConditionals() @addImplicitBracesAndParens() @addLocationDataToGeneratedTokens() @tokens
Rewrite the token stream, looking one token ahead and behind. Allow the return value of the block to tell us how many tokens to move forwards (or backwards) in the stream, to make sure we don't miss anything as tokens are inserted and removed, and the stream changes length under our feet.
scanTokens: (block) ->
{tokens} = this
i = 0
i += block.call this, token, i, tokens while token = tokens[i]
true
detectEnd: (i, condition, action) ->
{tokens} = this
levels = 0
while token = tokens[i]
return action.call this, token, i if levels is 0 and condition.call this, token, i
return action.call this, token, i - 1 if not token or levels < 0
if token[0] in EXPRESSION_START
levels += 1
else if token[0] in EXPRESSION_END
levels -= 1
i += 1
i - 1Leading newlines would introduce an ambiguity in the grammar, so we dispatch them here.
removeLeadingNewlines: -> break for [tag], i in @tokens when tag isnt 'TERMINATOR' @tokens.splice 0, i if i
Some blocks occur in the middle of expressions -- when we're expecting this, remove their trailing newlines.
removeMidExpressionNewlines: -> @scanTokens (token, i, tokens) -> return 1 unless token[0] is 'TERMINATOR' and @tag(i + 1) in EXPRESSION_CLOSE tokens.splice i, 1 0
The lexer has tagged the opening parenthesis of a method call. Match it with its paired close. We have the mis-nested outdent case included here for calls that close on the same line, just before their outdent.
closeOpenCalls: -> condition = (token, i) -> token[0] in [')', 'CALL_END'] or token[0] is 'OUTDENT' and @tag(i - 1) is ')' action = (token, i) -> @tokens[if token[0] is 'OUTDENT' then i - 1 else i][0] = 'CALL_END' @scanTokens (token, i) -> @detectEnd i + 1, condition, action if token[0] is 'CALL_START' 1
The lexer has tagged the opening parenthesis of an indexing operation call. Match it with its paired close.
closeOpenIndexes: -> condition = (token, i) -> token[0] in [']', 'INDEX_END'] action = (token, i) -> token[0] = 'INDEX_END' @scanTokens (token, i) -> @detectEnd i + 1, condition, action if token[0] is 'INDEX_START' 1
Match tags in token stream starting at i with pattern, skipping HERECOMMENTs Pattern may consist of strings (equality), an array of strings (one of) or null (wildcard)
matchTags: (i, pattern...) -> fuzz = 0 for j in [0 ... pattern.length] fuzz += 2 while @tag(i + j + fuzz) is 'HERECOMMENT' continue if not pattern[j]? pattern[j] = [pattern[j]] if typeof pattern[j] is 'string' return no if @tag(i + j + fuzz) not in pattern[j] yes
yes iff standing in front of something looking like
@
looksObjectish: (j) -> @matchTags(j, '@', null, ':') or @matchTags(j, null, ':')
yes iff current line of tokens contain an element of tags on same expression level. Stop searching at LINEBREAKS or explicit start of containing balanced expression.
findTagsBackwards: (i, tags) -> backStack = [] while i >= 0 and (backStack.length or @tag(i) not in tags and (@tag(i) not in EXPRESSION_START or @tokens[i].generated) and @tag(i) not in LINEBREAKS) backStack.push @tag(i) if @tag(i) in EXPRESSION_END backStack.pop() if @tag(i) in EXPRESSION_START and backStack.length i -= 1 @tag(i) in tags
Look for signs of implicit calls and objects in the token stream and add them.
addImplicitBracesAndParens: ->
Track current balancing depth (both implicit and explicit) on stack.
stack = [] @scanTokens (token, i, tokens) -> [tag] = token [prevTag] = if i > 0 then tokens[i - 1] else [] [nextTag] = if i < tokens.length - 1 then tokens[i + 1] else [] stackTop = -> stack[stack.length - 1] startIdx = i
Helper function, used for keeping track of the number of tokens consumed and spliced, when returning for getting a new token.
forward = (n) -> i - startIdx + nHelper functions
inImplicit = -> stackTop()?[2]?.ours inImplicitCall = -> inImplicit() and stackTop()?[0] is '(' inImplicitObject = -> inImplicit() and stackTop()?[0] is '{'
Unclosed control statement inside implicit parens (like class declaration or if-conditionals)
inImplicitControl = -> inImplicit and stackTop()?[0] is 'CONTROL' startImplicitCall = (j) -> idx = j ? i stack.push ['(', idx, ours: yes] tokens.splice idx, 0, generate 'CALL_START', '(' i += 1 if not j? endImplicitCall = -> stack.pop() tokens.splice i, 0, generate 'CALL_END', ')' i += 1 startImplicitObject = (j, startsLine = yes) -> idx = j ? i stack.push ['{', idx, sameLine: yes, startsLine: startsLine, ours: yes] tokens.splice idx, 0, generate '{', generate(new String('{')) i += 1 if not j? endImplicitObject = (j) -> j = j ? i stack.pop() tokens.splice j, 0, generate '}', '}' i += 1
Don't end an implicit call on next indent if any of these are in an argument
if inImplicitCall() and tag in ['IF', 'TRY', 'FINALLY', 'CATCH', 'CLASS', 'SWITCH'] stack.push ['CONTROL', i, ours: true] return forward(1) if tag is 'INDENT' and inImplicit()
An INDENT closes an implicit call unless
CONTROL argument on the line.if prevTag not in ['=>', '->', '[', '(', ',', '{', 'TRY', 'ELSE', '='] endImplicitCall() while inImplicitCall() stack.pop() if inImplicitControl() stack.push [tag, i] return forward(1)
Straightforward start of explicit expression
if tag in EXPRESSION_START stack.push [tag, i] return forward(1)
Close all implicit expressions inside of explicitly closed expressions.
if tag in EXPRESSION_END while inImplicit() if inImplicitCall() endImplicitCall() else if inImplicitObject() endImplicitObject() else stack.pop() stack.pop()
Recognize standard implicit calls like f a, f() b, f? c, h[0] d etc.
if (tag in IMPLICIT_FUNC and token.spaced and not token.stringEnd or tag is '?' and i > 0 and not tokens[i - 1].spaced) and (nextTag in IMPLICIT_CALL or nextTag in IMPLICIT_UNSPACED_CALL and not tokens[i + 1]?.spaced and not tokens[i + 1]?.newLine) tag = token[0] = 'FUNC_EXIST' if tag is '?' startImplicitCall i + 1 ret = forward(2) return ret
Implicit call taking an implicit indented object as first argument.
f
a: b
c: dand
f
1
a: b
b: cDon't accept implicit calls of this type, when on the same line as the control strucutures below as that may misinterpret constructs like:
if f
a: 1as
if f(a: 1)which is probably always unintended. Furthermore don't allow this in literal arrays, as that creates grammatical ambiguities.
if tag in IMPLICIT_FUNC and @matchTags(i + 1, 'INDENT', null, ':') and not @findTagsBackwards(i, ['CLASS', 'EXTENDS', 'IF', 'CATCH', 'SWITCH', 'LEADING_WHEN', 'FOR', 'WHILE', 'UNTIL']) startImplicitCall i + 1 stack.push ['INDENT', i + 2] return forward(3)
Implicit objects start here
if tag is ':'
Go back to the (implicit) start of the object
if @tag(i - 2) is '@' then s = i - 2 else s = i - 1 s -= 2 while @tag(s - 2) is 'HERECOMMENT' startsLine = s is 0 or @tag(s - 1) in LINEBREAKS or tokens[s - 1].newLine
Are we just continuing an already declared object?
if stackTop() [stackTag, stackIdx] = stackTop() if (stackTag is '{' or stackTag is 'INDENT' and @tag(stackIdx - 1) is '{') and (startsLine or @tag(s - 1) is ',' or @tag(s - 1) is '{') return forward(1) startImplicitObject(s, !!startsLine) return forward(2)
if prevTag is 'OUTDENT' and inImplicitCall() and tag in ['.', '?.', '::', '?::'] endImplicitCall() return forward(1) stackTop()[2].sameLine = no if inImplicitObject() and tag in LINEBREAKS if tag in IMPLICIT_END while inImplicit() [stackTag, stackIdx, {sameLine, startsLine}] = stackTop()
Close implicit calls when reached end of argument list
if inImplicitCall() and prevTag isnt ',' endImplicitCall()
Close implicit objects such as: return a: 1, b: 2 unless true
else if inImplicitObject() and sameLine and not startsLine endImplicitObject()
Close implicit objects when at end of line, line didn't end with a comma and the implicit object didn't start the line or the next line doesn't look like the continuation of an object.
else if inImplicitObject() and tag is 'TERMINATOR' and prevTag isnt ',' and not (startsLine and @looksObjectish(i + 1)) endImplicitObject() else break
Close implicit object if comma is the last character and what comes after doesn't look like it belongs. This is used for trailing commas and calls, like:
x =
a: b,
c: d,
e = 2and
f a, b: c, d: e, f, g: h: i, jif tag is ',' and not @looksObjectish(i + 1) and inImplicitObject() and (nextTag isnt 'TERMINATOR' or not @looksObjectish(i + 2))
When nextTag is OUTDENT the comma is insignificant and should just be ignored so embed it in the implicit object.
When it isn't the comma go on to play a role in a call or array further up the stack, so give it a chance.
offset = if nextTag is 'OUTDENT' then 1 else 0 while inImplicitObject() endImplicitObject i + offset return forward(1)
Add location data to all tokens generated by the rewriter.
addLocationDataToGeneratedTokens: -> @scanTokens (token, i, tokens) -> return 1 if token[2] return 1 unless token.generated or token.explicit if token[0] is '{' and nextLocation=tokens[i + 1]?[2] {first_line: line, first_column: column} = nextLocation else if prevLocation = tokens[i - 1]?[2] {last_line: line, last_column: column} = prevLocation else line = column = 0 token[2] = first_line: line first_column: column last_line: line last_column: column return 1
Because our grammar is LALR(1), it can't handle some single-line expressions that lack ending delimiters. The Rewriter adds the implicit blocks, so it doesn't need to. ')' can close a single-line block, but we need to make sure it's balanced.
addImplicitIndentation: -> starter = indent = outdent = null condition = (token, i) -> token[1] isnt ';' and token[0] in SINGLE_CLOSERS and not (token[0] is 'ELSE' and starter isnt 'THEN') and not (token[0] in ['CATCH', 'FINALLY'] and starter in ['->', '=>']) action = (token, i) -> @tokens.splice (if @tag(i - 1) is ',' then i - 1 else i), 0, outdent @scanTokens (token, i, tokens) -> [tag] = token if tag is 'TERMINATOR' and @tag(i + 1) is 'THEN' tokens.splice i, 1 return 0 if tag is 'ELSE' and @tag(i - 1) isnt 'OUTDENT' tokens.splice i, 0, @indentation()... return 2 if tag is 'CATCH' for j in [1..2] when @tag(i + j) in ['OUTDENT', 'TERMINATOR', 'FINALLY'] tokens.splice i + j, 0, @indentation()... return 2 + j if tag in SINGLE_LINERS and @tag(i + 1) isnt 'INDENT' and not (tag is 'ELSE' and @tag(i + 1) is 'IF') starter = tag [indent, outdent] = @indentation yes indent.fromThen = true if starter is 'THEN' tokens.splice i + 1, 0, indent @detectEnd i + 2, condition, action tokens.splice i, 1 if tag is 'THEN' return 1 return 1
Tag postfix conditionals as such, so that we can parse them with a different precedence.
tagPostfixConditionals: -> original = null condition = (token, i) -> [tag] = token [prevTag] = @tokens[i - 1] tag is 'TERMINATOR' or (tag is 'INDENT' and prevTag not in SINGLE_LINERS) action = (token, i) -> if token[0] isnt 'INDENT' or (token.generated and not token.fromThen) original[0] = 'POST_' + original[0] @scanTokens (token, i) -> return 1 unless token[0] is 'IF' original = token @detectEnd i + 1, condition, action return 1
Generate the indentation tokens, based on another token on the same line.
indentation: (implicit = no) -> indent = ['INDENT', 2] outdent = ['OUTDENT', 2] indent.generated = outdent.generated = yes if implicit indent.explicit = outdent.explicit = yes if not implicit [indent, outdent] generate: generate
Look up a tag by token index.
tag: (i) -> @tokens[i]?[0]
List of the token pairs that must be balanced.
BALANCED_PAIRS = [ ['(', ')'] ['[', ']'] ['{', '}'] ['INDENT', 'OUTDENT'], ['CALL_START', 'CALL_END'] ['PARAM_START', 'PARAM_END'] ['INDEX_START', 'INDEX_END'] ]
The inverse mappings of BALANCED_PAIRS we're trying to fix up, so we can
look things up from either end.
exports.INVERSES = INVERSES = {}The tokens that signal the start/end of a balanced pair.
EXPRESSION_START = [] EXPRESSION_END = [] for [left, rite] in BALANCED_PAIRS EXPRESSION_START.push INVERSES[rite] = left EXPRESSION_END .push INVERSES[left] = rite
Tokens that indicate the close of a clause of an expression.
EXPRESSION_CLOSE = ['CATCH', 'WHEN', 'ELSE', 'FINALLY'].concat EXPRESSION_END
Tokens that, if followed by an IMPLICIT_CALL, indicate a function invocation.
IMPLICIT_FUNC = ['IDENTIFIER', 'SUPER', ')', 'CALL_END', ']', 'INDEX_END', '@', 'THIS']
If preceded by an IMPLICIT_FUNC, indicates a function invocation.
IMPLICIT_CALL = [ 'IDENTIFIER', 'NUMBER', 'STRING', 'JS', 'REGEX', 'NEW', 'PARAM_START', 'CLASS' 'IF', 'TRY', 'SWITCH', 'THIS', 'BOOL', 'NULL', 'UNDEFINED', 'UNARY', 'SUPER' 'THROW', '@', '->', '=>', '[', '(', '{', '--', '++' ] IMPLICIT_UNSPACED_CALL = ['+', '-']
Tokens that always mark the end of an implicit call for single-liners.
IMPLICIT_END = ['POST_IF', 'FOR', 'WHILE', 'UNTIL', 'WHEN', 'BY', 'LOOP', 'TERMINATOR']
Single-line flavors of block expressions that have unclosed endings. The grammar can't disambiguate them, so we insert the implicit indentation.
SINGLE_LINERS = ['ELSE', '->', '=>', 'TRY', 'FINALLY', 'THEN'] SINGLE_CLOSERS = ['TERMINATOR', 'CATCH', 'FINALLY', 'ELSE', 'OUTDENT', 'LEADING_WHEN']
Tokens that end a line.
LINEBREAKS = ['TERMINATOR', 'INDENT', 'OUTDENT']
iced additions
IMPLICIT_FUNC.push 'DEFER' IMPLICIT_CALL.push 'DEFER' IMPLICIT_END.push 'AWAIT'