Follow a consistent user model

pkg/analysis_server/lib/src/services/completion/statement/design_notes.md

+# Statement Completion
+
+### Mission Statement
+
+The purpose of this feature is to add required syntax to the current
+statement. The goal is to make the statement syntactically complete.
+That is not possible to do in all cases. A best-effort attempt is made
+when it cannot be done.
+
+### Current Statement
+
+The term _statement completion_ comes from IntelliJ. It is also called
+_smart enter_ there, which is a more general term. See the IntelliJ
+[documentatopn.](https://www.jetbrains.com/help/idea/2017.1/auto-completing-code.html#statements_completion)

[devoncarew, 2017/05/09 13:15:06]

sp

[messick, 2017/05/09 13:26:03]

Done.

+
+Rather than restricting the functionality to statements, in the sense of the grammar construct
+called _statement_, it is best to think of code constructs. Statement completion
+can be used to add syntax to declarations, statements, and some expressions.
+Generally, the syntax additions are punctuation marks, such as semicolons,
+parentheses, and braces.
+
+The _current statement_ then, is the code construct being written in the
+editor, as identified by the position of the editing cursor. The _cursor_ is the
+primary editing cursor of the active editor in IntelliJ. We ignore multiple
+secondary cursors.
+
+If the _current statement_ is already syntactically complete then the feature
+just adds a newline. This will be the case when the cursor follows the closing
+brace of the body of a for-statement or while-statement, for example. The model
+used is that the user is creating code going forward, and when the
+_smart enter_ keystroke is typed the user expects to see forward progress.
+The cursor should end up at the most likely place to continue editing, regardless
+of what errors may exist in previous code. It is as if the user said "I'm done
+with this line. Finish it up and move me to the next line."
+
+## Code Constructs
+
+There are a number of cases where a matching right parenthesis could be added
+if it is missing. This feature has not been considered a priority since the
+editor by default adds parenthesis in pairs.
+
+Generics are not currently handled.
+
+#### Declarations
+
+There is limited work to be done.
+
+- [x] Functions, methods, and classes can have a pair of braces added if they do not already have a body defined.
+- [x] Functions and methods can have a closing parenthesis added to the parameter list.
+- [x] Variables can have a semicolon added to terminate them.
+
+#### Expressions
+
+Also limited.
+
+- [x] Unterminated strings can have appropriate string
+terminators added.
+- [x] Lists that have not been properly terminated can
+have closing brackets added (potentially with trailing commas).
+- [x] Maps are not currently handled. The parser error recovery
+gets confused by braces of code blocks too easily.
+
+#### Statements
+
+With actual statements, there are many more possibilities.
+Statements that start with a keyword must have at least the
+keyword in the partial statement in order for completion to
+happen.
+
+###### Do Statement
+
+This is one of the few cases where an actual word may be included.
+If the `while` keyword is missing it will be added.
+As long as the `do` keyword is present the braces for the body
+will be added. If the `while` keyword is present or can be added
+then the parentheses for the condition will be added, too. Finally,
+the terminating semicolon will be added.
+
+###### For Statement
+
+The parser cannot distinguish a for-statement from a for-each unless
+either at least one semicolon or the `in` keyword is present in the
+control parts. If neither is present then completion cannot do any
+more than possibly add braces for the body.
+
+Given that the statement is actually a for-statement then the control
+parts will be adjusted to ensure there are two semicolons. If the braces
+for the body are missing then they will be added.
+
+###### For-each Statement
+
+Braces for the body can be added if missing.
+
+###### If Statement
+
+The if-else-etc construct could get arbitrarily complex, so
+for simplicity the `else` keyword is ignored. Starting with nothing
+but the `if` keyword, the parentheses for the condition will be added
+and the braces for the body will be added.
+
+###### Switch Statement
+
+Given the `switch` keyword, parentheses for the selector will be added
+if absent and the braces for the body will be added. Also, for an
+individual case or default clause the terminating colon will be added
+if needed. To be clear, only the colon for the clause containing
+the cursor will be added.
+
+###### Try Statement
+
+If the statement is nothing more than the `try` keyword then the braces
+for the body will be added. No clauses (n, catch, or finally) will be added.
+
+An on-clause will be completed by adding braces for its body, if absent.
+
+A catch-clause will be completed by adding parentheses for its
+parameter list and braces for the body.
+
+A finally-clause will be completed by adding braces for its body.
+
+###### While Statement
+
+This is structurally identical to the if-statement and the implementation
+for both is shared.
+
+###### Expression Statements
+
+These include method and function invocations.
+- [x] Add closing parenthesis, if the expression is an invocation.
+- [x] Add terminating semicolon.
+
+###### Control-flow Blocks
+
+After finishing a `return` or `throw` in a block that is the
+body of a control-flow statement (do, for, for-each, if, while)
+then the cursor will be moved outside the block, ready to begin
+the next statement following the control-flow statement.
+```dart
+  if (isFinished()) {
+    releaseResources();
+    return; // invoke 'smart enter' here
+  }
+  // continue typing here
+```