TS1508: Unexpected '?'. Did you mean to escape it with backslash? shouldn't report even with v flag

🔎 Search Terms

TS1508, "Did you mean to escape it with backslash?"

🕗 Version & Regression Information

This changed between versions ______ and _______
This changed in Provide Syntax Checking for Regular Expressions #55600 which introduced regular expression syntax checking
This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play/?target=11#code/PQbQ-AZAusBuBQQ

💻 Code

/[?&]/v

🙁 Actual behavior

The error "TS1508: Unexpected '?'. Did you mean to escape it with backslash?" is given.

🙂 Expected behavior

No error because ? doesn't need to be escaped in a character class even with a v flag.

Additional information about the issue

Other characters like { do need escaping with the v flag, but ? gets no runtime errors, so I don't see why this has to err now.

This changed between versions 5.6.3 and 5.7.2

No, it was present in 5.6.3. Maybe you should edit it to "This changed in #55600 which introduced regular expression syntax checking"

A strange thing about this error is that it mentions ? but it is really about & (that's where the error squiggly is). If you escape the ? the error persists, and only goes away if you escape the &. Indeed it looks like the error talks about the first character (e.g., if you write /[\?&]/v to "fix" the error, the error stays but now it says "unexpected \"). So whether or not there's a bug around requiring & to be escaped (I think only && needs to be escaped, right?) there does seem to be a bug around the text of the message... so this is... two bug reports? Should we file another one (if neither are duplicates)?

This changed between versions 5.6.3 and 5.7.2

No, it was present in 5.6.3. Maybe you should edit it to "This changed in #55600 which introduced regular expression syntax checking"

I did check, but must have messed it up. Thanks!

A strange thing about this error is that it mentions ? but it is really about & (that's where the error squiggly is). If you escape the ? the error persists, and only goes away if you escape the &. Indeed it looks like the error talks about the first character (e.g., if you write /[\?&]/v to "fix" the error, the error stays but now it says "unexpected \"). So whether or not there's a bug around requiring & to be escaped (I think only && needs to be escaped, right?)

Right. /[?&&]/v gives an error in Chrome, for example, while /[?&]/v does not.

graphemecluster (@graphemecluster)

Paging graphemecluster (@graphemecluster)

The incorrectly reported character gets fixed by this patch:

diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 343df39ad9..3619f57180 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -3103,7 +3103,7 @@ export function createScanner(
                     operand = scanClassSetOperand();
                     break;
             }
-            switch (charCodeChecked(pos)) {
+            switch (ch = charCodeChecked(pos)) {
                 case CharacterCodes.minus:
                     if (charCodeChecked(pos + 1) === CharacterCodes.minus) {
                         if (isCharacterComplement && mayContainStrings) {

But the other part of the issue would have to be investigated further.

These 3 lines shouldn't have been there in the first place 😄

diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 343df39ad9..986a3dcf5a 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -3125,9 +3125,6 @@ export function createScanner(
                         mayContainStrings = !isCharacterComplement && expressionMayContainStrings;
                         return;
                     }
-                    else {
-                        error(Diagnostics.Unexpected_0_Did_you_mean_to_escape_it_with_backslash, pos, 1, String.fromCharCode(ch));
-                    }
                     break;
                 default:
                     if (isCharacterComplement && mayContainStrings) {

Remove a mistaken error in `scanClassSetExpression` (microsoft/TypeSc…

I fixed lone & handling in /v character classes and added a compiler regression test for it asw.

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TS1508: Unexpected '?'. Did you mean to escape it with backslash? shouldn't report even with `v` flag #62707

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TS1508: Unexpected '?'. Did you mean to escape it with backslash? shouldn't report even with v flag #62707

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🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

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jcalz commented on Nov 2, 2025

brettz9 commented on Nov 2, 2025

RyanCavanaugh commented on Nov 3, 2025

Andarist commented on Nov 3, 2025

graphemecluster commented on Nov 4, 2025

Ijtihed commented on Jun 5, 2026

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TS1508: Unexpected '?'. Did you mean to escape it with backslash? shouldn't report even with `v` flag #62707