emacs: replace cd with pushd/popd in buildPhase of melpaBuild

It is better to not change the working directory.

One example showing the benefit is the rewriting[1] of lspce, where
the Rust build hook assumes the working directory is unchanged.

[1]: https://github.com/NixOS/nixpkgs/pull/334476

pkgs/applications/editors/emacs/build-support/melpa.nix

@@ -111,7 +111,7 @@ genericBuild ({
   buildPhase = ''
     runHook preBuild
 
-    cd "$NIX_BUILD_TOP"
+    pushd "$NIX_BUILD_TOP"
 
     emacs --batch -Q \
         -L "$NIX_BUILD_TOP/package-build" \
@@ -119,6 +119,8 @@ genericBuild ({
         -f melpa2nix-build-package \
         $ename $melpaVersion $commit
 
+    popd
+
     runHook postBuild
     '';
 

pkgs/applications/editors/emacs/elisp-packages/manual-packages/lsp-bridge/default.nix

@@ -77,7 +77,6 @@ melpaBuild {
   checkPhase = ''
     runHook preCheck
 
-    cd "$sourceRoot"
     mkfifo test.log
     cat < test.log &
     HOME=$(mktemp -d) python -m test.test

pkgs/applications/editors/emacs/elisp-packages/melpa-packages.nix

@@ -186,13 +186,13 @@ let
           buildInputs = old.buildInputs ++ [ pkgs.sqlite ];
 
           postBuild = ''
-            cd source/sqlite
+            pushd sqlite
             make
-            cd -
+            popd
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
-            install -m=755 -D source/sqlite/emacsql-sqlite \
+            install -m=755 -D sqlite/emacsql-sqlite \
               $out/share/emacs/site-lisp/elpa/emacsql-${old.version}/sqlite/emacsql-sqlite
           '';
 
@@ -203,13 +203,13 @@ let
           buildInputs = old.buildInputs ++ [ pkgs.sqlite ];
 
           postBuild = ''
-            cd source/sqlite
+            pushd sqlite
             make
-            cd -
+            popd
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
-            install -m=755 -D source/sqlite/emacsql-sqlite \
+            install -m=755 -D sqlite/emacsql-sqlite \
               $out/share/emacs/site-lisp/elpa/emacsql-sqlite-${old.version}/sqlite/emacsql-sqlite
           '';
 
@@ -296,7 +296,7 @@ let
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
-            install source/hotfuzz-module.so $out/share/emacs/site-lisp/elpa/hotfuzz-*
+            install hotfuzz-module.so $out/share/emacs/site-lisp/elpa/hotfuzz-*
           '';
         });
 
@@ -304,17 +304,17 @@ let
           cmakeFlags = old.cmakeFlags or [ ] ++ [ "-DCMAKE_INSTALL_BINDIR=bin" ];
           env.NIX_CFLAGS_COMPILE = "-UCLANG_RESOURCE_DIR";
           preConfigure = ''
-            cd server
+            pushd server
           '';
           preBuild = ''
             make
             install -D bin/irony-server $out/bin/irony-server
-            cd ..
+            popd
           '';
           checkPhase = ''
-            cd source/server
+            pushd server
             make check
-            cd ../..
+            popd
           '';
           preFixup = ''
             rm -rf $out/share/emacs/site-lisp/elpa/*/server
@@ -343,18 +343,14 @@ let
           buildInputs = (old.buildInputs or [ ]) ++ [ pkgs.enchant2 ];
 
           postBuild = ''
-            pushd working/jinx
             NIX_CFLAGS_COMPILE="$($PKG_CONFIG --cflags enchant-2) $NIX_CFLAGS_COMPILE"
             $CC -shared -o jinx-mod${libExt} jinx-mod.c -lenchant-2
-            popd
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
-            pushd source
             outd=$(echo $out/share/emacs/site-lisp/elpa/jinx-*)
             install -m444 --target-directory=$outd jinx-mod${libExt}
             rm $outd/jinx-mod.c $outd/emacs-module.h
-            popd
           '';
 
           meta = old.meta // {
@@ -366,17 +362,13 @@ let
           buildInputs = (old.buildInputs or [ ]) ++ [ pkgs.sqlite ];
 
           postBuild = ''
-            pushd working/sqlite3
             make
-            popd
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
-            pushd source
             outd=$out/share/emacs/site-lisp/elpa/sqlite3-*
             install -m444 -t $outd sqlite3-api.so
             rm $outd/*.c $outd/*.h
-            popd
           '';
 
           meta = old.meta // {
@@ -539,14 +531,14 @@ let
           '';
 
           postBuild = ''
-            cd source/server
+            pushd server
             make
-            cd -
+            popd
           '';
 
           postInstall = (old.postInstall or "") + "\n" + ''
             mkdir -p $out/bin
-            install -m755 -Dt $out/bin ./source/server/telega-server
+            install -m755 -Dt $out/bin server/telega-server
           '';
         });
 
@@ -676,10 +668,8 @@ let
           # we need the proper out directory to exist, so we do this in the
           # postInstall instead of postBuild
           postInstall = (old.postInstall or "") + "\n" + ''
-            pushd source/build >/dev/null
             make
             install -m444 -t $out/share/emacs/site-lisp/elpa/vterm-** ../*.so
-            popd > /dev/null
             rm -rf $out/share/emacs/site-lisp/elpa/vterm-**/{CMake*,build,*.c,*.h}
           '';
         });
@@ -717,8 +707,7 @@ let
             buildInputs =
               old.buildInputs ++
               (with pkgs.darwin.apple_sdk.frameworks; [CoreServices Foundation]);
-            buildPhase = (old.buildPhase or "") + ''
-              cd source
+            postBuild = (old.postBuild or "") + ''
               $CXX -O3 -framework CoreServices -framework Foundation osx-dictionary.m -o osx-dictionary-cli
             '';
             postInstall = (old.postInstall or "") + "\n" + ''