Fix bug 27 of #17340 (#19433)

Fixes silent disappearance of Markdown (pseudo-)link when it's detected as
unsafe protocol. Now it will be converted to plain text in spirit of
[the specification](https://spec.commonmark.org/0.30/#links).
For that sake the check for protocol is added to rst.nim also.

tests/stdlib/trst.nim

@@ -843,12 +843,7 @@ suite "Warnings":
               rnInner
                 rnLeaf  'foo'
               rnInner
-                rnLeaf  '#'
-                rnLeaf  'foo'
-                rnLeaf  ','
-                rnLeaf  'string'
-                rnLeaf  ','
-                rnLeaf  'string'
+                rnLeaf  '#foo,string,string'
           rnParagraph  anchor='foo'
             rnLeaf  'Paragraph'
             rnLeaf  '.'
@@ -1256,3 +1251,23 @@ suite "RST inline markup":
           rnLeaf  'my {link example'
           rnLeaf  'http://example.com/bracket_(symbol_[)'
       """)
+
+  test "not a Markdown link":
+    # bug #17340 (27) `f` will be considered as a protocol and blocked as unsafe
+    var warnings = new seq[string]
+    check("[T](f: var Foo)".toAst(warnings = warnings) ==
+      dedent"""
+        rnInner
+          rnLeaf  '['
+          rnLeaf  'T'
+          rnLeaf  ']'
+          rnLeaf  '('
+          rnLeaf  'f'
+          rnLeaf  ':'
+          rnLeaf  ' '
+          rnLeaf  'var'
+          rnLeaf  ' '
+          rnLeaf  'Foo'
+          rnLeaf  ')'
+      """)
+    check(warnings[] == @["input(1, 5) Warning: broken link 'f'"])

tests/stdlib/trstgen.nim

@@ -1593,8 +1593,15 @@ suite "invalid targets":
   test "invalid links":
     check("(([Nim](https://nim-lang.org/)))".toHtml ==
         """((<a class="reference external" href="https://nim-lang.org/">Nim</a>))""")
-    check("(([Nim](javascript://nim-lang.org/)))".toHtml ==
-        """((<a class="reference external" href="">Nim</a>))""")
+    # unknown protocol is treated just like plain text, not a link
+    var warnings = new seq[string]
+    check("(([Nim](javascript://nim-lang.org/)))".toHtml(warnings=warnings) ==
+        """(([Nim](javascript://nim-lang.org/)))""")
+    check(warnings[] == @["input(1, 9) Warning: broken link 'javascript'"])
+    warnings[].setLen 0
+    check("`Nim <javascript://nim-lang.org/>`_".toHtml(warnings=warnings) ==
+      """Nim &lt;javascript://nim-lang.org/&gt;""")
+    check(warnings[] == @["input(1, 33) Warning: broken link 'javascript'"])
 
 suite "local file inclusion":
   test "cannot include files in sandboxed mode":