Extend cover.erl source search

Commit 29231033 made cover fall back to compile info if source was not
found in pwd or ../src. This isn't sufficient for source that lies in
subdirectories of ../src when beams and source have been moved since
compilation (eg. install of some OTP applications), so first try finding
source relative to the beam directory.

For example, given a beam path

  /installed/path/to/app-1.0/ebin/root.beam

and a source path

  /compiled/path/to/app/src/subdir/root.erl

then look for

  /installed/path/to/app-1.0/ebin/../src/subdir/root.erl

before the source path.

2 files changed, 57 insertions, 38 deletions

diff --git a/lib/tools/doc/src/cover.xml b/lib/tools/doc/src/cover.xml
index 477871d6c3..beefd4ee8d 100644
--- a/lib/tools/doc/src/cover.xml
+++ b/lib/tools/doc/src/cover.xml
@@ -316,8 +316,13 @@
           <c>compile_beam_directory/0,1</c>, it is assumed that the
           source code can be found in the same directory as the
           <c>.beam</c> file, in <c>../src</c> relative to that
-          directory, or at the source path in
-          <c>Module:module_info(compile)</c>. If no source code is found,
+          directory, or using the source path in
+          <c>Module:module_info(compile)</c>. When using the latter,
+          two paths are examined: first the one constructed by
+          joining <c>../src</c> and the tail of the compiled path
+          below a trailing <c>src</c> component, then the compiled
+          path itself.
+          If no source code is found,
           <c>{error,no_source_code_found}</c> is returned.</p>
 	<p>HINT: It is possible to issue multiple analyse_to_file commands at
 	  the same time. </p> 
diff --git a/lib/tools/src/cover.erl b/lib/tools/src/cover.erl
index 2579711dc7..dfcfc3675f 100644
--- a/lib/tools/src/cover.erl
+++ b/lib/tools/src/cover.erl
@@ -1951,47 +1951,61 @@ move_clauses([{M,F,A,C,_L}|Clauses]) ->
     move_clauses(Clauses);
 move_clauses([]) ->
     ok.
-			  
 
 %% Given a .beam file, find the .erl file. Look first in same directory as
-%% the .beam file, then in <beamdir>/../src
+%% the .beam file, then in ../src, then in compile info.
 find_source(Module, File0) ->
-    case filename:rootname(File0,".beam") of
-	File0 ->
-	    File0;
-	File ->
-	    InSameDir = File++".erl",
-	    case filelib:is_file(InSameDir) of
-		true -> 
-		    InSameDir;
-		false ->
-		    Dir = filename:dirname(File),
-		    Mod = filename:basename(File),
-		    InDotDotSrc = filename:join([Dir,"..","src",Mod++".erl"]),
-		    case filelib:is_file(InDotDotSrc) of
-			true ->
-			    InDotDotSrc;
-			false ->
-			    find_source_from_module(Module, File0)
-		    end
-	    end
+    try
+        Root = filename:rootname(File0, ".beam"),
+        Root == File0 andalso throw(File0),  %% not .beam
+        %% Look for .erl in pwd.
+        File = Root ++ ".erl",
+        throw_file(File),
+        %% Not in pwd: look in ../src.
+        BeamDir = filename:dirname(File),
+        Base = filename:basename(File),
+        throw_file(filename:join([BeamDir, "..", "src", Base])),
+        %% Not in ../src: look for source path in compile info, but
+        %% first look relative the beam directory.
+        Info = lists:keyfind(source, 1, Module:module_info(compile)),
+        false == Info andalso throw({beam, File0}),  %% stripped
+        {source, SrcFile} = Info,
+        throw_file(splice(BeamDir, SrcFile)),  %% below ../src
+        throw_file(SrcFile),                   %% or absolute
+        %% No success means that source is either not under ../src or
+        %% its relative path differs from that of compile info. (For
+        %% example, compiled under src/x but installed under src/y.)
+        %% An option to specify an arbitrary source path explicitly is
+        %% probably a better solution than either more heuristics or a
+        %% potentially slow filesystem search.
+        {beam, File0}
+    catch
+        Path -> Path
     end.
 
-%% In case we can't find the file from the given .beam,
-%% we try to get the information directly from the module source
-find_source_from_module(Module, File) ->
-    Compile = Module:module_info(compile),
-    case lists:keyfind(source, 1, Compile) of
-	{source, Path} ->
-	    case filelib:is_file(Path) of
-		true ->
-		    Path;
-		false ->
-		    {beam, File}
-	    end;
-	false ->
-		{beam, File}
-	end.
+throw_file(Path) ->
+    false /= Path andalso filelib:is_file(Path) andalso throw(Path).
+
+%% Splice the tail of a source path, starting from the last "src"
+%% component, onto the parent of a beam directory, or return false if
+%% no "src" component is found.
+%%
+%% Eg. splice("/path/to/app-1.0/ebin", "/compiled/path/to/app/src/x/y.erl")
+%%        --> "/path/to/app-1.0/ebin/../src/x/y.erl"
+%%
+%% This handles the case of source in subdirectories of ../src with
+%% beams that have moved since compilation.
+%%
+splice(BeamDir, SrcFile) ->
+    case lists:splitwith(fun(C) -> C /= "src" end, revsplit(SrcFile)) of
+        {T, [_|_]} ->  %% found src component
+            filename:join([BeamDir, "..", "src" | lists:reverse(T)]);
+        {_, []} ->     %% or not
+            false
+    end.
+
+revsplit(Path) ->
+    lists:reverse(filename:split(Path)).
 
 do_parallel_analysis(Module, Analysis, Level, Loaded, From, State) ->
     analyse_info(Module,State#main_state.imported),