Adjusted initializer rules, changing a run-time error to compile-time.

docs/language/dartLangSpec.tex

Index: docs/language/dartLangSpec.tex
diff --git a/docs/language/dartLangSpec.tex b/docs/language/dartLangSpec.tex
index adec30a2e00e590efe76c15cc15a11f27686fd0d..3d011a80a8eb20294a41deac36e524b692e465a1 100644
--- a/docs/language/dartLangSpec.tex
+++ b/docs/language/dartLangSpec.tex
@@ -1411,7 +1411,13 @@ An initializer list begins with a colon, and consists of a comma-separated list
 \end{grammar}
 
 \LMHash{}
-Let $k$ be a generative constructor.  Then $k$ may include at most one  superinitializer in its initializer list or a compile-time error occurs. If no superinitializer is provided, an implicit superinitializer of the form \SUPER{}() is added at the end of $k$'s initializer list, unless the enclosing class is class \code{Object}. It is a compile-time error if more than one initializer corresponding to a given instance variable appears in $k$'s initializer list. It is a compile-time error if $k$'s initializer list contains an initializer for a variable that is initialized by means of an initializing formal of $k$. % It is a compile-time error if  $k$'s initializer list contains an initializer for a final variable $f$ whose declaration includes an initialization expression.
+Let $k$ be a generative constructor.
+Then $k$ may include at most one superinitializer in its initializer list or a compile-time error occurs.
+If no superinitializer is provided, an implicit superinitializer of the form \SUPER{}() is added at the end of $k$'s initializer list,
+unless the enclosing class is class \code{Object}.
+It is a compile-time error if more than one initializer corresponding to a given instance variable appears in $k$'s initializer list.
+It is a compile-time error if $k$'s initializer list contains an initializer for a variable that is initialized by means of an initializing formal of $k$.

[Lasse Reichstein Nielsen, 2017/04/25 16:00:23]

Interesting that this is an error, even if it's not a final variable, but I
guess we still consider this a "local" duplicate.

[eernst, 2017/05/19 11:17:02]

Acknowledged. I think the clashes "2 initializers", "initializer + init.formal"
are so semantically similar and so local that it makes sense to treat them
identically as an error.

+It is a compile-time error if $k$'s initializer list contains an initializer for a final variable $f$ whose declaration includes an initialization expression.

[Lasse Reichstein Nielsen, 2017/04/25 16:00:23]

Should we handle the case of initializing formal + initialization expression of
final variable here too?
And having two formal initializers with the same name? (Or is that handled by it
introducing the same name to the scope twice?)

That would make all the dedup-rules be together.

[eernst, 2017/05/19 11:17:02]

Yep, that's (now) a name clash in the formal parameter initializer scope, so we
don't need to specify any other errors there.
 
As far as I can see, the rule that makes "init.formal + final variable
initializer" an error (or even mentions this case) is new, but we discussed it
and I think we agreed to include it.

I just created an issue (#29656) such that we will get it implemented and have
some test cases.

 
 \LMHash{}
 Each final instance variable $f$ declared in the immediately enclosing class must have an initializer in $k$'s initializer list unless it has already been initialized by one of the following means:
@@ -1497,8 +1503,7 @@ proceeds as follows:
 
 \LMHash{}
 First, the expression $e$ is evaluated to an object $o$.
-%%STRONG_MODE: The runtime error in the next sentence will be compile-time.
-Then, the instance variable $v$ of $i$ is bound to $o$, unless $v$ is a final variable that has already been initialized, in which case a runtime error occurs.
+Then, the instance variable $v$ of $i$ is bound to $o$.
 In checked mode, it is a dynamic type error if $o$ is not \NULL{} and the interface of the class of $o$ is not a subtype of the actual type of the instance variable $v$.
 
 \LMHash{}