Disallow expressions statements starting with `{`.
The current specification only prohibits expressions statements where the
expression *is* a map, not those that *start with* a map.
Implementations have always rejected those starting with a map.
Bug: http://dartbug.com/725
Change-Id: I805a6f82d1afdcf335aff73e74dac1f14e5a6afe
Reviewed-on: https://dart-review.googlesource.com/71247
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>
diff --git a/docs/language/dartLangSpec.tex b/docs/language/dartLangSpec.tex
index 8e19bd2..051d913 100644
--- a/docs/language/dartLangSpec.tex
+++ b/docs/language/dartLangSpec.tex
@@ -25,6 +25,8 @@
% constructor invocation.
% - Specify that type arguments passed in a redirecting factory constructor
% declaration must be taken into account during static checks.
+% - Disallow any expression statement starting with `{`, not just
+% those that are map literals.
%
% 2.0
% - Don't allow functions as assert test values.
@@ -7826,11 +7828,8 @@
\LMLabel{expressionStatements}
\LMHash{}
-An {\em expression statement} consists of an expression other than a non-constant map literal (\ref{maps}) that has no explicit type arguments.
-
-\rationale{
-The restriction on maps is designed to resolve an ambiguity in the grammar, when a statement begins with \{.
-}
+An {\em expression statement} consists of an expression that does not
+begin with a \{ character.
\begin{grammar}
{\bf expressionStatement:}expression? `{\escapegrammar ;}'
@@ -7838,11 +7837,24 @@
\end{grammar}
\LMHash{}
-Execution of an expression statement \code{$e$;} proceeds by evaluating $e$.
+The expression of an expression statement is not allowed to begin with a \{.
+\commentary{
+This means that if some source text could otherwise be parsed as an expression
+followed by a \;, then this grammar production does not apply
+when the expression starts with a \{.
+}
+\rationale{
+The restriction resolves an ambiguity while parsing where a
+\{ can start either a block (\ref{blocks}) or a map literal (\ref{maps}).
+By disallowing the latter from starting an expression statement,
+the parser does not need to look further ahead
+before deciding that it is parsing a block statement.
+}
\LMHash{}
-It is a compile-time error if a non-constant map literal that has no explicit type arguments appears in a place where a statement is expected.
-
+Execution of an expression statement \code{$e$;} proceeds by evaluating $e$.
+If the expression evaluates to a value, then the value is ignored
+and the execution completes normally.
\subsection{Local Variable Declaration}
\LMLabel{localVariableDeclaration}
