Merge pull request #89 from JuliaLang/cjf/README-ast

Add notes about AST differences + minor recovery fix

Author: c42f

README.md

@@ -435,6 +435,22 @@ julia> text = "x = \"\"\"\n    \$a\n    b\"\"\""
     21:23     │    """                      "\"\"\""
 ```
 
+### Less redundant `block`s
+
+Sometimes `Expr` needs to contain redundant block constructs in order to have a
+place to store `LineNumberNode`s, but we don't need these and avoid adding them
+in several cases:
+* The right hand side of short form function syntax
+* The conditional in `elseif`
+* The body of anonymous functions after the `->`
+
+### Distinct conditional ternary expression
+
+The syntax `a ? b : c` is the same as `if a b else c` in `Expr` so macros can't
+distinguish these cases. Instead, we use a distinct expression head `K"?"` and
+lower to `Expr(:if)` during `Expr` conversion.
+
+
 ## More about syntax kinds
 
 We generally track the type of syntax nodes with a syntax "kind", stored

src/parser.jl

@@ -3244,7 +3244,6 @@ function parse_atom(ps::ParseState, check_identifiers=true)
     if leading_kind == K":"
         # symbol/expression quote
         # :foo  ==>  (quote foo)
-        # : foo  ==>  (quote (error-t) foo)
         t = peek_token(ps, 2)
         k = kind(t)
         if is_closing_token(ps, k) && (!is_keyword(k) || preceding_whitespace(t))
@@ -3256,19 +3255,12 @@ function parse_atom(ps::ParseState, check_identifiers=true)
         end
         bump(ps, TRIVIA_FLAG) # K":"
         if preceding_whitespace(t)
-            # : a  ==> (quote (error-t) a))
-            # ===
-            # :
-            # a
-            # ==> (quote (error))
-            bump_trivia(ps, TRIVIA_FLAG,
+            # : foo   ==>  (quote (error-t) foo)
+            # :\nfoo  ==>  (quote (error-t) foo)
+            bump_trivia(ps, TRIVIA_FLAG, skip_newlines=true,
                         error="whitespace not allowed after `:` used for quoting")
             # Heuristic recovery
-            if kind(t) == K"NewlineWs"
-                bump_invisible(ps, K"error")
-            else
-                bump(ps)
-            end
+            bump(ps)
         else
             # Being inside quote makes keywords into identifiers at at the
             # first level of nesting

test/parser.jl

@@ -568,10 +568,12 @@ tests = [
     ],
     JuliaSyntax.parse_atom => [
         ":foo"   => "(quote foo)"
-        ": foo"  => "(quote (error-t) foo)"
         # Literal colons
         ":)"     => ":"
         ": end"  => ":"
+        # Whitespace after quoting colon
+        ": foo"  => "(quote (error-t) foo)"
+        ":\nfoo" => "(quote (error-t) foo)"
         # plain equals
         "="      => "(error =)"
         # Identifiers