fixes docgen regression: don't add newLine for code if it's the first line (#23154)

Before (devel)


![image](https://github.com/nim-lang/Nim/assets/43030857/cde37109-027a-46c1-a37e-1d6062e6c609)

After (this PR and stable)


![image](https://github.com/nim-lang/Nim/assets/43030857/3366877c-7223-4749-a584-fe93f731281f)

It now keeps the same behavior as before

lib/packages/docutils/rst.nim

@@ -1603,6 +1603,7 @@ proc parseMarkdownCodeblock(p: var RstParser): PRstNode =
   else:
     args = nil
   var n = newLeaf("")
+  var isFirstLine = true
   while true:
     if currentTok(p).kind == tkEof:
       rstMessage(p, meMissingClosing,
@@ -1614,7 +1615,8 @@ proc parseMarkdownCodeblock(p: var RstParser): PRstNode =
       inc p.idx, 2
       break
     elif currentTok(p).kind == tkIndent:
-      n.text.add "\n"
+      if not isFirstLine:
+        n.text.add "\n"
       if currentTok(p).ival > baseCol:
         n.text.add " ".repeat(currentTok(p).ival - baseCol)
       elif currentTok(p).ival < baseCol:
@@ -1624,6 +1626,7 @@ proc parseMarkdownCodeblock(p: var RstParser): PRstNode =
     else:
       n.text.add(currentTok(p).symbol)
       inc p.idx
+    isFirstLine = false
   result.sons[0] = args
   if result.sons[2] == nil:
     var lb = newRstNode(rnLiteralBlock)

nimdoc/test_doctype/expected/test_doctype.html

@@ -62,8 +62,7 @@
     <div id="tocRoot"></div>
     
     <p class="module-desc"><p>Check</p>
-<p><pre class="listing">
-<span class="Identifier">text</span></pre></p>
+<p><pre class="listing"><span class="Identifier">text</span></pre></p>
 
 <h1><a class="toc-backref" id="check" href="#check">Check</a></h1>
 <h1><a class="toc-backref" id="text" href="#text">text</a></h1></p>

tests/stdlib/trst.nim

@@ -526,8 +526,7 @@ suite "RST parsing":
             rnFieldBody
               rnLeaf  'Nim'
         rnLiteralBlock
-          rnLeaf  '
-      let a = 1
+          rnLeaf  'let a = 1
       ```'
       """
 
@@ -637,8 +636,7 @@ suite "RST parsing":
                 rnLeaf  'test'
               rnFieldBody
           rnLiteralBlock
-            rnLeaf  '
-        let a = 1'
+            rnLeaf  'let a = 1'
         """)
 
     check(dedent"""
@@ -661,8 +659,7 @@ suite "RST parsing":
               rnFieldBody
                 rnLeaf  '1'
           rnLiteralBlock
-            rnLeaf  '
-        let a = 1'
+            rnLeaf  'let a = 1'
         """)
 
   test "additional indentation < 4 spaces is handled fine":
@@ -682,8 +679,7 @@ suite "RST parsing":
                 rnLeaf  'nim'
               [nil]
               rnLiteralBlock
-                rnLeaf  '
-          let a = 1'
+                rnLeaf  '  let a = 1'
       """)
       # | |
       # |  \ indentation of exactly two spaces before 'let a = 1'
@@ -717,8 +713,7 @@ suite "RST parsing":
                   rnFieldBody
                     rnLeaf  'Nim'
               rnLiteralBlock
-                rnLeaf  '
-        CodeBlock()'
+                rnLeaf  'CodeBlock()'
             rnLeaf  ' '
             rnLeaf  'Other'
             rnLeaf  ' '

tests/stdlib/trstgen.nim

@@ -1246,7 +1246,7 @@ Test1
         "input(8, 4) Warning: language 'anotherLang' not supported"
         ])
     check(output == "<pre class = \"listing\">anything</pre>" &
-                    "<p><pre class = \"listing\">\nsomeCode</pre> </p>")
+                    "<p><pre class = \"listing\">someCode</pre> </p>")
 
   test "RST admonitions":
     # check that all admonitions are implemented