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

[brettz9]

🔎 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.

[jcalz]

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)?

[brettz9]

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.

[RyanCavanaugh]

Paging @graphemecluster

[Andarist]

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.

[graphemecluster]

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) {