Distinguish between ternary's : and arrow fn's return type (#573)

* Distinguish between ternary's : and arrow fn's return type

* Correctly parse nested arrow functions inside conditional expressions

Defer the conversion of arrow function parameters to assignable nodes so that
it is possible to use the (invalid) ast to get the exact position of the (wrong)
arrow functions.

* Check params of arrow fns w/ type params or w/o return type

* Fix also async functions

* Add test from prettier

https://github.com/prettier/prettier/issues/2194

* Don't check arrow params if they are valid at the first attemp

* Use state instead of relying on the "noArrowParamsConversion" parameter

* Remove noArrowParamsConversion

test/fixtures/flow/regression/issue-58-ambiguous/actual.js

@@ -0,0 +1,4 @@
+// This can be parsed in two ways:
+// a ? b : (c => ((d): e => f))
+// a ? ((b): c => d) : (e => f)
+a ? (b) : c => (d) : e => f;

test/fixtures/flow/regression/issue-58-ambiguous/options.json

@@ -0,0 +1,3 @@
+{
+    "throws": "Ambiguous expression: wrap the arrow functions in parentheses to disambiguate. (4:4)"
+}

test/fixtures/flow/regression/issue-58-failing-1/actual.js

@@ -0,0 +1,2 @@
+// Function which looks like a return type
+a ? (b) : (c => d) => e;

test/fixtures/flow/regression/issue-58-failing-1/options.json

@@ -0,0 +1,3 @@
+{
+    "throws": "Invalid left-hand side in arrow function parameters (2:11)"
+}

test/fixtures/flow/regression/issue-58-failing-2/actual.js

@@ -0,0 +1,2 @@
+// Invalid LHS parameter after type parameters
+a ? <T>(b => c) : d => (e) : f => g;

test/fixtures/flow/regression/issue-58-failing-2/options.json

@@ -0,0 +1,3 @@
+{
+    "throws": "Invalid left-hand side in arrow function parameters (2:8)"
+}

test/fixtures/flow/regression/issue-58-failing-3/actual.js

@@ -0,0 +1,2 @@
+// Invalid LHS parameter after type parameters
+a ? (b => c) => (e) : f => g;

test/fixtures/flow/regression/issue-58-failing-3/options.json

@@ -0,0 +1,3 @@
+{
+    "throws": "Invalid left-hand side in arrow function parameters (2:5)"
+}

test/fixtures/flow/regression/issue-58-failing-4/actual.js

@@ -0,0 +1,2 @@
+// Invalid LHS parameter
+a ? async (b => c) => (d) : f => g;

test/fixtures/flow/regression/issue-58-failing-4/options.json

@@ -0,0 +1,3 @@
+{
+    "throws": "Invalid left-hand side in arrow function parameters (2:11)"
+}

test/fixtures/flow/regression/issue-58/actual.js

@@ -0,0 +1,44 @@
+// Valid lhs value inside parentheses
+a ? (b) : c => d; // a ? b : (c => d)
+a ? (b) : c => d : e; // a ? ((b): c => d) : e
+a ? (b) : (c) : d => e; // a ? b : ((c): d => e)
+
+// Nested arrow function inside parentheses
+a ? (b = (c) => d) : e => f; // a ? (b = (c) => d) : (e => f)
+a ? (b = (c) => d) : e => f : g; // a ? ((b = (c) => d): e => f) : g
+
+// Nested conditional expressions
+    b ? c ? (d) : e => (f) : g : h; // b ? (c ? ((d): e => f) : g) : h
+a ? b ? c ? (d) : e => (f) : g : h; // a ? (b ? (c ? d : (e => f)) : g) : h
+
+a ? b ? (c) : (d) : (e) => f : g; // a ? (b ? c : ((d): e => f)) : g
+
+// Multiple arrow functions
+a ? (b) : c => d : (e) : f => g; // a ? ((b): c => d) : ((e): f => g)
+
+// Multiple nested arrow functions (<T> is needed to avoid ambiguities)
+a ? (b) : c => (d) : e => f : g; // a ? ((b): c => ((d): e => f)) : g
+a ? (b) : c => <T>(d) : e => f; // a ? b : (c => (<T>(d): e => f))
+a ? <T>(b) : c => (d) : e => f; // a ? (<T>(b): c => d) : (e => f)
+
+// Invalid lhs value inside parentheses
+a ? (b => c) : d => e; // a ? (b => c) : (d => e)
+a ? b ? (c => d) : e => f : g; // a ? (b ? (c => d) : (e => f)) : g
+
+// Invalid lhs value inside parentheses inside arrow function
+a ? (b) : c => (d => e) : f => g; // a ? ((b): c => (d => e)) : (f => g)
+a ? b ? (c => d) : e => (f => g) : h => i; // a ? (b ? (c => d) : (e => (f => g))) : (h => i)
+
+// Function as type annotation
+a ? (b) : (c => d) => e : f; // a ? ((b): (c => d) => e) : f
+
+// Async functions or calls
+a ? async (b) : c => d; // a ? (async(b)) : (c => d)
+a ? async (b) : c => d : e; // a ? (async (b): c => d) : e
+a ? async (b => c) : d => e; // a ? (async(b => c)) : (d => e)
+a ? async (b) => (c => d) : e => f; // a ? (async (b) => c => d) : (e => f)
+
+// https://github.com/prettier/prettier/issues/2194
+let icecream = what == "cone"
+  ? p => (!!p ? `here's your ${p} cone` : `just the empty cone for you`)
+  : p => `here's your ${p} ${what}`;