Fix off-by-one column tracking for $-prefixed identifiers

The pattern `('$':x:cs)` consumes two characters (the '$' and the first
identifier character 'x'), so the remaining input `cs` starts at column
`c+2`, not `c+1`.

This bug caused incorrect column positions to be reported for Verilog
system tasks like $display, $finish, $time, etc. All subsequent tokens
on the same line after a $-identifier would have their column numbers
off by one.

---------

Co-authored-by: Jiuyang Liu <liu@jiuyang.me>

Author: quark17

src/comp/Lex.hs

@@ -278,7 +278,7 @@ lx lf f l c (ch:cs) | isDigit ch =
   in
     case span isDigit cs of
     (s', cs') -> lxFloat (ch:s') cs'
-lx lf f l c ('$':x:cs) | isIdChar x = spanId [] (c+1) cs
+lx lf f l c ('$':x:cs) | isIdChar x = spanId [] (c+2) cs
     where spanId r cn (y:cs) | (isIdChar y || y == '$') = spanId (y:r) (cn+1) cs
           spanId r cn cs' =
              let fs = mkFString ('$':x:reverse r)

testsuite/bsc.syntax/bh/LexPos.bs testsuite/bsc.syntax/bh/LexPos_NumLit.bstestsuite/bsc.syntax/bh/LexPos.bs renamed to testsuite/bsc.syntax/bh/LexPos_NumLit.bs

@@ -1,4 +1,4 @@
-package LexPos where
+package LexPos_NumLit where
 
 x :: Integer
 x = 5 + 9 + "foo"

testsuite/bsc.syntax/bh/LexPos_Task.bs

@@ -0,0 +1,13 @@
+package LexPos_Task where
+
+-- Both 'f' and 'g' should have a type error at column 14
+-- as the reference to 'x' is at the same column in both
+
+f :: Bool -> Action
+f x = $fwrite x
+
+g :: Bool -> Action
+g x = dfwrite x
+
+dfwrite :: File -> Action
+dfwrite x = $fwrite x

testsuite/bsc.syntax/bh/bh.exp

@@ -112,11 +112,26 @@ compile_pass_bug EmptyDo_Braces.bs
 # Confirm that the failure was due to an internal error
 find_regexp [make_bsc_output_name EmptyDo_Braces.bs] {Internal.*Error}
 
+# -----
+# Test lexer positions
+
+proc check_lex_pos { srcname linepos colpos {errtag T0020} {count 1}} {
+    set str "Error: \"$srcname\", line $linepos, column $colpos: ($errtag)"
+    find_n_strings [make_bsc_output_name $srcname] $str $count
+}
+
 # Fix position after numeric literals with prefixes
 # (fixes Google issue #77395569)
-compile_fail LexPos.bs
-find_n_strings LexPos.bs.bsc-out {Error: "LexPos.bs", line 4, column 12: (T0020)} 1
-find_n_strings LexPos.bs.bsc-out {Error: "LexPos.bs", line 7, column 16: (T0020)} 1
+compile_fail LexPos_NumLit.bs
+check_lex_pos LexPos_NumLit.bs 4 12
+check_lex_pos LexPos_NumLit.bs 7 16
+
+# Fix position after system task names (prefixed with dollarsign)
+compile_fail LexPos_Task.bs
+check_lex_pos LexPos_Task.bs 7 14
+check_lex_pos LexPos_Task.bs 10 14
+
+# -----
 
 # Allow _ in numeric literals
 # (fixes Google issue #67326190)

testsuite/bsc.typechecker/display/NotDisplayable.bs.bsc-out.expected

@@ -1,6 +1,6 @@
 checking package dependencies
 compiling NotDisplayable.bs
-Error: "NotDisplayable.bs", line 6, column 14: (T0031)
+Error: "NotDisplayable.bs", line 6, column 15: (T0031)
   The contexts for this expression could not be resolved because there are no
   instances of the form:
     Prelude.Bits NotDisplayable.Test a__

testsuite/bsc.typechecker/display/NotListDisplay.bs.bsc-out.expected

@@ -1,6 +1,6 @@
 checking package dependencies
 compiling NotListDisplay.bs
-Error: "NotListDisplay.bs", line 6, column 17: (T0031)
+Error: "NotListDisplay.bs", line 6, column 18: (T0031)
   The contexts for this expression could not be resolved because there are no
   instances of the form:
     Prelude.Bits (Prelude.List a) a__