Improve error message for keywords as parameters (#25052)

A function with an illegal parameter name like
```nim
proc myproc(type: int) =
  echo type
```
would uninformatively fail like so:
```nim
tkeywordparam.nim(1, 13) Error: expected closing ')'
```

This commit makes it return the following error:
```nim
tkeywordparam.nim(1, 13) Error: 'type' is a keyword and cannot be used as a parameter name
```

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Emre Şafak <[email protected]>
Co-authored-by: Andreas Rumpf <[email protected]>

Author: 3 people

compiler/parser.nim

@@ -1156,7 +1156,10 @@ proc parseParamList(p: var Parser, retColon = true): PNode =
         parMessage(p, errGenerated, "the syntax is 'parameter: var T', not 'var parameter: T'")
         break
       else:
-        parMessage(p, "expected closing ')'")
+        if p.tok.tokType in tokKeywordLow..tokKeywordHigh:
+          parMessage(p, errGenerated, "'" & $p.tok.ident.s & "' is a keyword and cannot be used as a parameter name")
+        else:
+          parMessage(p, "expected closing ')'")
         break
       result.add(a)
       if p.tok.tokType notin {tkComma, tkSemiColon}: break

tests/errmsgs/tkeywordparam.nim

@@ -0,0 +1,10 @@
+discard """
+cmd: "nim check $file"
+errormsg: "'type' is a keyword and cannot be used as a parameter name"
+nimout: '''
+tkeywordparam.nim(1, 13) Error: 'type' is a keyword and cannot be used as a parameter name
+'''
+"""
+
+proc myproc(type: int) =
+  echo type