[Git][ghc/ghc][wip/T25784] Collapse string gaps as \& (#25784)

[Brandon Chinn (@brandonchinn178)]

Brandon Chinn pushed to branch wip/T25784 at Glasgow Haskell Compiler / GHC


Commits:
58b0625a by Brandon Chinn at 2025-02-24T18:07:07-08:00
Collapse string gaps as \& (#25784)

In 9.10, "\65\ \0" would result in "A0", but in 9.12, it results in
"\650", due to the string refactoring I did in !13128. Previously, we
were resolving escape codes and collapsing string gaps as we come across
them, but after the refactor, string processing is broken out into
phases, which is both more readable and useful for multiline strings.

- - - - -


4 changed files:

- compiler/GHC/Parser/String.hs
- + testsuite/tests/parser/should_run/T25784.hs
- + testsuite/tests/parser/should_run/T25784.stdout
- testsuite/tests/parser/should_run/all.T


Changes:

=====================================
compiler/GHC/Parser/String.hs
=====================================
@@ -127,7 +127,8 @@ collapseGaps = go
   where
     go = \case
       c1@(Char '\\') : c2@(Char c) : cs
-        | is_space c -> go $ dropGap cs
+        -- #25784: string gaps are semantically equivalent to "\&"
+        | is_space c -> c1 : setChar '&' c1 : go (dropGap cs)
         | otherwise  -> c1 : c2 : go cs
       c : cs -> c : go cs
       [] -> []


=====================================
testsuite/tests/parser/should_run/T25784.hs
=====================================
@@ -0,0 +1,18 @@
+{-# LANGUAGE MultilineStrings #-}
+
+main :: IO ()
+main = do
+  checkEqual "\65\  \0" "A0"
+  checkEqual
+    """
+      a
+    \
+    \  b
+    """
+    "  a\n  b"
+
+checkEqual :: String -> String -> IO ()
+checkEqual actual expected = do
+  putStrLn $ "Expected: " ++ show expected
+  putStrLn $ "Actual:   " ++ show actual
+  putStrLn "========================================"


=====================================
testsuite/tests/parser/should_run/T25784.stdout
=====================================
@@ -0,0 +1,6 @@
+Expected: "A0"
+Actual:   "A0"
+========================================
+Expected: "  a\n  b"
+Actual:   "  a\n  b"
+========================================


=====================================
testsuite/tests/parser/should_run/all.T
=====================================
@@ -27,3 +27,4 @@ test('MultilineStrings', normal, compile_and_run, [''])
 test('MultilineStringsOverloaded', normal, compile_and_run, [''])
 test('T25375', normal, compile_and_run, [''])
 test('T25609', normal, compile_and_run, [''])
+test('T25784', normal, compile_and_run, [''])



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/58b0625ab6b5dec11ae540f15c45015b906d0ac2

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/58b0625ab6b5dec11ae540f15c45015b906d0ac2
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