build: Place target in meson build dir

Instead of putting target/ and in the source
directory, we can tell our cargo script to put both target
and our cargo-home in meson's build directory. This means
that when triggering a rebuild through meson via tooling
like Builder, Fractal will actually rebuild.

.gitlab-ci.yml

@@ -16,7 +16,7 @@ variables:
         key: "flatpak"
         paths:
           - .flatpak-builder/cache/
-          - target/
+          - _build/target/
           - target_docs/
           - target_test/
 

fractal-gtk/src/meson.build

@@ -46,6 +46,7 @@ cargo_release = custom_target('cargo-build',
                         command: [cargo_script,
                                   '@SOURCE_ROOT@',
                                   '@OUTPUT@',
+                                  meson.build_root(),
                                   profile
                                  ])
 

scripts/cargo.sh

@@ -1,13 +1,15 @@
 #!/bin/sh
 
-export CARGO_HOME=$1/target/cargo-home
-export FRACTAL_PROFILE="$3"
+export OUTPUT="$2"
+export CARGO_TARGET_DIR="$3"/target
+export CARGO_HOME="$CARGO_TARGET_DIR"/cargo-home
+export FRACTAL_PROFILE="$4"
 
 if [ "$FRACTAL_PROFILE" = "Devel" ]
 then
     echo "DEBUG MODE"
-    cargo build --manifest-path $1/Cargo.toml -p fractal-gtk && cp $1/target/debug/fractal-gtk $2
+    cargo build --manifest-path $1/Cargo.toml -p fractal-gtk && cp "$CARGO_TARGET_DIR"/debug/fractal-gtk "$OUTPUT"
 else
     echo "RELEASE MODE"
-    cargo build --manifest-path $1/Cargo.toml --release -p fractal-gtk && cp $1/target/release/fractal-gtk $2
+    cargo build --manifest-path $1/Cargo.toml --release -p fractal-gtk && cp "$CARGO_TARGET_DIR"/release/fractal-gtk "$OUTPUT"
 fi