[VM] Parameterized map literal used as a statement doesn't cause an error

[DartBot]

This issue was originally filed by [email protected]

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What steps will reproduce the problem?
Simplest example:
main() {
  <Map>{};
}

What is the expected output? What do you see instead?
Expecting a compile-time error per spec, not seeing one.

What version of the product are you using? On what operating system?
VM build r8882

[DartBot]

This comment was originally written by @mhausner

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Can you please reference the relevant spec portion? From what I remember, the intent was to break the ambiguity of a { at the beginning of a statement by specifying it to be a block, never a map literal. But a map literal with type arguments should be fine at the beginning of a statement.

[DartBot]

This comment was originally written by [email protected]

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11.2 Expression Statements
An expression statement consists of an expression other than a map literal (10.7).
expressionStatement:
expression? `;'
;
Execution of an expression statement e; proceeds by evaluating e.
It is a compile-time error if a map literal appears in a place where a statement
is expected.

[DartBot]

This comment was originally written by @mhausner

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Thank you. I just spoke to Gilad. He agrees that this should only apply to map literals that start with a curly brace. That is, a map literal with type arguments is ok. He will update the spec accordingly.

(The main issue this restriction solves is to disambiguate between map literal and beginning of a block, both of which start with a { token. )

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cc @gbracha.

[gbracha]

Relevant spec snippet in 0.11

An expression statement consists of an expression other than a non-constant map literal that has no explicit type arguments.

[DartBot]

This comment was originally written by @mhausner

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Thanks Gilad. This makes the bug "invalid". I'll mark it as "fixed" since we fixed the spec instead of the compiler :)

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Added Area-Language, Fixed labels.

[DartBot]

This comment was originally written by [email protected]

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fix the last sentence of that chapter too, please