use different hook with amsthm, issue #304

hyperref.dtx

@@ -10990,6 +10990,26 @@
        }%
      }%  
   } 
+%    \end{macrocode}
+% amsthm doesn't issue an item in the theorem, we delay the target into
+% \cs{deferred@thm@head} and hope that it always begins a paragraph.
+%    \begin{macrocode}
+\AddToHook{package/amsthm/after}
+ {
+  \renewcommand\Hy@theorem@refstepcounter[1]
+   {%
+    \H@refstepcounter{#1}%
+    \hyper@makecurrent{#1}%
+    \global\let\Hy@dth@currentHref\@currentHref
+    \AddToHookNext{cmd/deferred@thm@head/before}
+     {\AddToHookNext{para/begin}
+       {\let\Hy@tempa\@currentHref
+        \MakeLinkTarget*{\Hy@dth@currentHref}%
+        \global\let\@currentHref\Hy@tempa
+       }%
+     }%  
+   }
+ }  
 \@ifundefined{hyper@nopatch@thm}{%  
 \AtBeginDocument{%  
  \@ifpackageloaded{cleveref}

testfiles-pdftex/gh304-amsthm.lvt

@@ -0,0 +1,17 @@
+\documentclass{article}
+\input{regression-test}
+\usepackage{amsthm}
+\usepackage{hyperref}
+
+\newtheorem{theorem}{Theorem}
+
+\begin{document}
+\START \showoutput
+
+\begin{theorem} 
+bla \label{thm:lab}
+\end{theorem}
+
+\ref{thm:lab}
+
+\end{document}

testfiles-pdftex/gh304-amsthm.tlg

@@ -0,0 +1,85 @@
+This is a generated file for the l3build validation system.
+Don't change this file in any respect.
+Completed box being shipped out [1]
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+.....\glue 0.0 plus 1.0fil
+.\kern 0.0
+(gh304-amsthm.aux)
+Package rerunfilecheck Info: File `gh304-amsthm.out' has not changed.
+(rerunfilecheck)             Checksum: D41D8CD98F00B204E9800998ECF8427E;0.