From 6fb439cec22e1e710cd7c3c4c2268e3d97c2f98b Mon Sep 17 00:00:00 2001
From: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
Date: Fri, 20 May 2022 16:10:41 -0400
Subject: [PATCH] Accommodate internal initial-digit identifiers

The motivating example is the `xyzIsSymbol` style of variable name that
can be created by `CoreFn.CSE`.
---
 .../internal_accommodate-initial-digit-idents.md |  1 +
 src/Language/PureScript/CodeGen/JS/Common.hs     |  7 +++++--
 tests/purs/passing/CSEInitialDigitSymbols.purs   | 16 ++++++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 CHANGELOG.d/internal_accommodate-initial-digit-idents.md
 create mode 100644 tests/purs/passing/CSEInitialDigitSymbols.purs

diff --git a/CHANGELOG.d/internal_accommodate-initial-digit-idents.md b/CHANGELOG.d/internal_accommodate-initial-digit-idents.md
new file mode 100644
index 0000000000..d5e162db70
--- /dev/null
+++ b/CHANGELOG.d/internal_accommodate-initial-digit-idents.md
@@ -0,0 +1 @@
+* Accommodate internally-generated identifiers that start with digits
diff --git a/src/Language/PureScript/CodeGen/JS/Common.hs b/src/Language/PureScript/CodeGen/JS/Common.hs
index b3fd2c46d1..cdb34d3e36 100644
--- a/src/Language/PureScript/CodeGen/JS/Common.hs
+++ b/src/Language/PureScript/CodeGen/JS/Common.hs
@@ -19,9 +19,12 @@ moduleNameToJs (ModuleName mn) =
 --
 --  * Alphanumeric characters are kept unmodified.
 --
---  * Reserved javascript identifiers are prefixed with '$$'.
+--  * Reserved javascript identifiers and identifiers starting with digits are
+--    prefixed with '$$'.
 identToJs :: Ident -> Text
-identToJs (Ident name) = anyNameToJs name
+identToJs (Ident name)
+  | not (T.null name) && isDigit (T.head name) = "$$" <> T.concatMap identCharToText name
+  | otherwise = anyNameToJs name
 identToJs (GenIdent _ _) = internalError "GenIdent in identToJs"
 identToJs UnusedIdent = unusedIdent
 identToJs (InternalIdent RuntimeLazyFactory) = "$runtime_lazy"
diff --git a/tests/purs/passing/CSEInitialDigitSymbols.purs b/tests/purs/passing/CSEInitialDigitSymbols.purs
new file mode 100644
index 0000000000..0a015754bc
--- /dev/null
+++ b/tests/purs/passing/CSEInitialDigitSymbols.purs
@@ -0,0 +1,16 @@
+module Main where
+
+import Data.Symbol (class IsSymbol, reflectSymbol)
+import Effect.Console (log)
+import Type.Proxy (Proxy(..))
+
+reflectSymbol' :: forall s. IsSymbol s => Proxy s -> String
+reflectSymbol' = reflectSymbol
+
+two = reflectSymbol (Proxy :: _ "2")
+two2 = reflectSymbol' (Proxy :: _ "2")
+
+twoThirty = reflectSymbol (Proxy :: _ "2:30")
+twoThirty2 = reflectSymbol' (Proxy :: _ "2:30")
+
+main = log "Done"