erl_docgen: Add hover links for ghlink

All functions, datatype and h3 headings have gotten a hover
attribute that shows a link directly to the edit page on
github for easy editing of documentation.

The github link links to the maint branch. An early attempt
was done to use the SHA of the current branch, but that did
not work well as github can only take pull requests from
branches.

3 files changed, 187 insertions, 46 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 814997b21d..d4d4dd7f31 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -53,14 +53,14 @@
 
   <datatypes>
     <datatype>
-      <name>ext_binary()</name>
+      <name name="ext_binary"/>
       <desc>
         <p>A binary data object, structured according to
           the Erlang external term format.</p>
       </desc>
     </datatype>
     <datatype>
-      <name>iovec()</name>
+      <name name="iovec"/>
       <desc>
         <p>A list of binaries. This datatype is useful to use
           together with <seealso marker="erl_nif#enif_inspect_iovec">
diff --git a/lib/erl_docgen/priv/css/otp_doc.css b/lib/erl_docgen/priv/css/otp_doc.css
index 66ea09b53a..69ecf151e4 100644
--- a/lib/erl_docgen/priv/css/otp_doc.css
+++ b/lib/erl_docgen/priv/css/otp_doc.css
@@ -242,8 +242,24 @@ th {
  font-size: small;
 }
 
-h3>a, h4>a{
- color: #1a1a1a !important;
+.title_link {
+    color: #1a1a1a !important;
+    outline: none;
+}
+
+.ghlink {
+    margin-left: -2.7em; /* .pencil.font-size + .pencil.padding.left + .pencil.padding.right = 2.7 */
+    visibility: hidden;
+}
+
+.pencil:before {
+    content: "\270D";
+    color: #1a1a1a !important;
+    font-weight: bold;
+    font-size: 1.5em;
+    padding: .3em .6em .6em;
+    line-height: 1em;
+    font-family: mono;
 }
 
 hr{
diff --git a/lib/erl_docgen/priv/xsl/db_html.xsl b/lib/erl_docgen/priv/xsl/db_html.xsl
index f9f3a356be..d92241277d 100644
--- a/lib/erl_docgen/priv/xsl/db_html.xsl
+++ b/lib/erl_docgen/priv/xsl/db_html.xsl
@@ -54,6 +54,19 @@
     <func:result select="$result"/>
   </func:function>
 
+  <func:function name="erl:lower-case">
+    <xsl:param name="str"/>
+
+    <xsl:variable name="uppercase" select="'ABCDEFGHIJKLMNOPQRSTUVWXYZ'"/>
+    <xsl:variable name="lowercase" select="'abcdefghijklmnopqrstuvwxyz'"/>
+
+    <xsl:variable name="result">
+      <xsl:value-of select="translate($str, $uppercase, $lowercase)"/>
+    </xsl:variable>
+
+    <func:result select="$result"/>
+  </func:function>
+
   <!-- Used from template menu.funcs to sort a module's functions for the lefthand index list,
        from the module's .xml file. Returns a value on which to sort the entity in question
        (a <name> element).
@@ -208,6 +221,7 @@
 	<xsl:variable name="local_types"
 		      select="../type[string-length(@name) > 0]"/>
 	<xsl:apply-templates select="$spec/contract/clause/head">
+          <xsl:with-param name="ghlink" select="ancestor-or-self::*[@ghlink]/@ghlink"/>
 	  <xsl:with-param name="local_types" select="$local_types"/>
 	  <xsl:with-param name="global_types" select="$global_types"/>
 	</xsl:apply-templates>
@@ -216,9 +230,17 @@
   </xsl:template>
 
   <xsl:template match="head">
+    <xsl:param name="ghlink"/>
     <xsl:param name="local_types"/>
     <xsl:param name="global_types"/>
-    <div class="bold_code func-head">
+    <xsl:variable name="id" select="concat(concat(concat(concat(../../../name,'-'),../../../arity),'-'),generate-id(.))"/>
+    <div class="bold_code func-head"
+         onMouseOver="document.getElementById('ghlink-{$id}').style.visibility = 'visible';"
+         onMouseOut="document.getElementById('ghlink-{$id}').style.visibility = 'hidden';">
+      <xsl:call-template name="ghlink">
+        <xsl:with-param name="ghlink" select="$ghlink"/>
+        <xsl:with-param name="id" select="$id"/>
+      </xsl:call-template>
       <xsl:apply-templates mode="local_type">
         <xsl:with-param name="local_types" select="$local_types"/>
         <xsl:with-param name="global_types" select="$global_types"/>
@@ -403,24 +425,35 @@
 
   <!-- Datatypes -->
   <xsl:template match="datatypes">
-    <h3>
-        <a name="data-types" href="#data-types"><xsl:text>Data Types</xsl:text></a>
-    </h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Data Types</xsl:with-param>
+    </xsl:call-template>
     <xsl:apply-templates/>
   </xsl:template>
 
-  <!-- Datatype Title-->
+  <!-- Datatype Title, is the really needed? not used by anything -->
   <xsl:template match="datatype_title">
-     <xsl:variable name="title" select="."/>
-     <h4>
-        <a name="{$title}" href="#{$title}"><xsl:apply-templates/></a>
+    <xsl:variable name="title" select="."/>
+    <h4>
+      <xsl:call-template name="title_link">
+        <xsl:with-param name="title"><xsl:apply-templates/></xsl:with-param>
+        <xsl:with-param name="link" select="$title"/>
+      </xsl:call-template>
     </h4>
   </xsl:template>
 
   <!-- Datatype -->
   <xsl:template match="datatype">
+    <xsl:variable name="id" select="concat('type-',name/@name)"/>
     <div class="data-types-body">
-      <div class="data-type-name"><xsl:apply-templates select="name"/></div>
+      <div class="data-type-name"
+           onMouseOver="document.getElementById('ghlink-{$id}').style.visibility = 'visible';"
+           onMouseOut="document.getElementById('ghlink-{$id}').style.visibility = 'hidden';">
+        <xsl:call-template name="ghlink">
+          <xsl:with-param name="id" select="$id"/>
+        </xsl:call-template>
+        <xsl:apply-templates select="name"/>
+      </div>
       <div class="data-type-desc"><xsl:apply-templates select="desc"/></div>
     </div>
   </xsl:template>
@@ -904,7 +937,7 @@
 
  <!-- Header -->
  <xsl:template match="header"/>
-  
+
  <!-- Section/Title -->
  <xsl:template match="section/title"/>
 
@@ -917,10 +950,13 @@
       <xsl:for-each select="marker">
 	<xsl:call-template name="marker-before-title"/>
       </xsl:for-each>
-      <a name="{generate-id(title)}">
-        <xsl:value-of select="$chapnum"/>.<xsl:number/>&#160;
-        <xsl:value-of select="title"/>
-      </a>
+      <xsl:call-template name="title_link">
+        <xsl:with-param name="link" select="generate-id(title)"/>
+        <xsl:with-param name="title">
+          <xsl:value-of select="$chapnum"/>.<xsl:number/>&#160;
+          <xsl:value-of select="title"/>
+        </xsl:with-param>
+      </xsl:call-template>
     </h3>
     <xsl:apply-templates>
       <xsl:with-param name="chapnum" select="$chapnum"/>
@@ -937,7 +973,9 @@
 	<xsl:call-template name="marker-before-title"/>
       </xsl:for-each>
       <!-- xsl:value-of select="$partnum"/>.<xsl:value-of select="$chapnum"/>.<xsl:value-of select="$sectnum"/>.<xsl:number/ -->
-      <xsl:value-of select="title"/>
+      <xsl:call-template name="title_link">
+        <xsl:with-param name="title" select="title"/>
+      </xsl:call-template>
     </h4>
     <xsl:apply-templates>
       <xsl:with-param name="chapnum" select="$chapnum"/>
@@ -967,9 +1005,9 @@
       <xsl:for-each select="marker">
 	<xsl:call-template name="marker-before-title"/>
       </xsl:for-each>
-      <a name="{generate-id(title)}">
-        <xsl:value-of select="title"/>
-      </a>
+      <xsl:call-template name="title_link">
+        <xsl:with-param name="title" select="title"/>
+      </xsl:call-template>
     </h3>
     <div class="REFBODY rb-3">
     <xsl:apply-templates>
@@ -1813,7 +1851,9 @@
   <!-- Module -->
   <xsl:template match="module">
     <xsl:param name="partnum"/>
-    <h3><a name="module" href="#module">Module</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Module</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY module-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1825,7 +1865,9 @@
   <!-- Modulesummary -->
   <xsl:template match="modulesummary">
     <xsl:param name="partnum"/>
-    <h3><a name="module-summary" href="#module-summary">Module Summary</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Module Summary</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY module-summary-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1836,7 +1878,9 @@
   <!-- Lib -->
   <xsl:template match="lib">
     <xsl:param name="partnum"/>
-    <h3><a name="c-library" href="#c-library">C Library</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">C Library</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY c-library-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1848,7 +1892,9 @@
   <!-- Libsummary -->
   <xsl:template match="libsummary">
     <xsl:param name="partnum"/>
-    <h3><a name="library-summary" href="#library-summary">Library Summary</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Library Summary</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY library-summary-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1859,7 +1905,9 @@
   <!-- Com -->
   <xsl:template match="com">
     <xsl:param name="partnum"/>
-    <h3><a name="command" href="#command">Command</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Command</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY command-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1871,7 +1919,9 @@
   <!-- Comsummary -->
   <xsl:template match="comsummary">
     <xsl:param name="partnum"/>
-    <h3><a name="command-summary" href="#command-summary">Command Summary</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Command Summary</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY command-summary-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1882,7 +1932,9 @@
   <!-- File -->
   <xsl:template match="file">
     <xsl:param name="partnum"/>
-    <h3><a name="file" href="#file">File</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">File</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY file-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1894,7 +1946,9 @@
   <!-- Filesummary -->
   <xsl:template match="filesummary">
     <xsl:param name="partnum"/>
-    <h3><a name="file-summary" href="#file-summary">File Summary</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">File Summary</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY file-summary-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1906,7 +1960,9 @@
   <!-- App -->
   <xsl:template match="app">
     <xsl:param name="partnum"/>
-    <h3><a name="application" href="#application">Application</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Application</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY application-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1918,7 +1974,9 @@
   <!-- Appsummary -->
   <xsl:template match="appsummary">
     <xsl:param name="partnum"/>
-    <h3><a name="application-summary" href="#application-summary">Application Summary</a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Application Summary</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY application-summary-body">
       <xsl:apply-templates>
         <xsl:with-param name="partnum" select="$partnum"/>
@@ -1929,7 +1987,9 @@
   <!-- Description -->
   <xsl:template match="description">
     <xsl:param name="partnum"/>
-    <h3><a name="description" href="#description">Description</a></h3>
+        <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Description</xsl:with-param>
+    </xsl:call-template>
     <div class="REFBODY description-body">
       <p>
         <xsl:apply-templates>
@@ -1943,7 +2003,9 @@
   <xsl:template match="funcs">
     <xsl:param name="partnum"/>
 
-    <h3><a name="exports" href="#exports"><xsl:text>Exports</xsl:text></a></h3>
+    <xsl:call-template name="h3_title_link">
+      <xsl:with-param name="title">Exports</xsl:with-param>
+    </xsl:call-template>
 
     <div class="exports-body">
         <xsl:apply-templates>
@@ -1960,7 +2022,8 @@
     <p><xsl:apply-templates select="name"/>
        <xsl:apply-templates
            select="name[string-length(@arity) > 0 and position()=last()]"
-           mode="types"/></p>
+           mode="types"/>
+    </p>
 
     <xsl:apply-templates select="fsummary|type|desc">
       <xsl:with-param name="partnum" select="$partnum"/>
@@ -2019,14 +2082,19 @@
 
     <xsl:choose>
       <xsl:when test="ancestor::cref">
-        <a name="{substring-before(nametext, '(')}">
-          <span class="bold_code bc-7">
-            <xsl:value-of select="ret"/>
-            <xsl:call-template name="maybe-space-after-ret">
-              <xsl:with-param name="s" select="ret"/>
-            </xsl:call-template>
-            <xsl:value-of select="nametext"/>
-          </span></a><br/>
+        <span class="bold_code bc-7">
+          <xsl:call-template name="title_link">
+            <xsl:with-param name="link" select="substring-before(nametext, '(')"/>
+            <xsl:with-param name="title">
+              <xsl:value-of select="ret"/>
+              <xsl:call-template name="maybe-space-after-ret">
+                <xsl:with-param name="s" select="ret"/>
+              </xsl:call-template>
+              <xsl:value-of select="nametext"/>
+            </xsl:with-param>
+          </xsl:call-template>
+        </span>
+        <br/>
       </xsl:when>
       <xsl:when test="ancestor::erlref">
         <xsl:variable name="fname">
@@ -2047,15 +2115,29 @@
         </xsl:variable>
 	<xsl:choose>
 	  <xsl:when test="ancestor::datatype">
-            <a name="type-{$fname}"></a><span class="bold_code bc-8"><xsl:apply-templates/></span><br/>
+            <div class="bold_code bc-8">
+              <xsl:call-template name="title_link">
+                <xsl:with-param name="link" select="concat('type-',$fname)"/>
+                <xsl:with-param name="title">
+                  <xsl:apply-templates/>
+                </xsl:with-param>
+              </xsl:call-template>
+            </div>
 	  </xsl:when>
           <xsl:otherwise>
-            <a name="{$fname}-{$arity}"></a><span class="bold_code fun-type"><xsl:apply-templates/></span><br/>
+            <div class="bold_code fun-type">
+              <xsl:call-template name="title_link">
+                <xsl:with-param name="link" select="concat(concat($fname,'-'),$arity)"/>
+                <xsl:with-param name="title">
+                  <xsl:apply-templates/>
+                </xsl:with-param>
+              </xsl:call-template>
+            </div>
           </xsl:otherwise>
 	</xsl:choose>
       </xsl:when>
       <xsl:otherwise>
-        <span class="bold_code bc-10"><xsl:value-of select="."/></span>
+        <div class="bold_code bc-10"><xsl:value-of select="."/></div>
       </xsl:otherwise>
     </xsl:choose>
 
@@ -2115,6 +2197,49 @@
     </div>
   </xsl:template>
 
+  <xsl:template name="h3_title_link">
+    <xsl:param name="title"/>
+    <h3>
+      <xsl:call-template name="title_link">
+        <xsl:with-param name="title" select="$title"/>
+        <xsl:with-param name="link" select="translate(erl:lower-case($title),' ','-')"/>
+      </xsl:call-template>
+    </h3>
+  </xsl:template>
+
+  <xsl:template name="title_link">
+    <xsl:param name="title"/>
+    <xsl:param name="link" select="generate-id(title)"/>
+    <xsl:param name="ghlink" select="ancestor-or-self::*[@ghlink][position() = 1]/@ghlink"/>
+    <xsl:variable name="id" select="concat(concat($link,'-'), generate-id(.))"/>
+    <span onMouseOver="document.getElementById('ghlink-{$id}').style.visibility = 'visible';"
+          onMouseOut="document.getElementById('ghlink-{$id}').style.visibility = 'hidden';">
+      <xsl:call-template name="ghlink">
+          <xsl:with-param name="id" select="$id"/>
+          <xsl:with-param name="ghlink" select="$ghlink"/>
+      </xsl:call-template>
+      <a class="title_link" name="{$link}" href="#{$link}"><xsl:value-of select="$title"/></a>
+    </span>
+  </xsl:template>
+
+  <xsl:template name="ghlink">
+    <xsl:param name="id"/>
+    <xsl:param name="ghlink" select="ancestor-or-self::*[@ghlink][position() = 1]/@ghlink"/>
+    <xsl:choose>
+      <xsl:when test="string-length($ghlink) > 0">
+        <span id="ghlink-{$id}" class="ghlink">
+          <a href="https://github.com/erlang/otp/edit/{$ghlink}"
+             title="Found an issue with the documentation? Fix it by clicking here!">
+            <span class="pencil"/>
+          </a>
+        </span>
+      </xsl:when>
+      <xsl:otherwise>
+        <span id="ghlink-{$id}"/>
+      </xsl:otherwise>
+    </xsl:choose>
+  </xsl:template>
+
   <!-- Desc -->
   <xsl:template match="desc">
     <xsl:param name="partnum"/>