Build: Use meson_Cargo.toml.in for setting up the build

to make rust-analyzer work correctly.

When the paths in Cargo.toml have '@path@' in them,
rust-analyzer cannot find the correct paths.

Before this change, rust-analyzer was unable to offer information
about code (in files other than main.rs), and instead
showed an error-message:
"1:1 unused: This file is not included anywhere in the module tree,
so rust-analyzer can't offer IDE services.".

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/657>

Cargo.toml

@@ -5,21 +5,21 @@ edition = "2021"
 
 [lib]
 name = "rs"
-path = "@path@/src/lib.rs"
+path = "src/lib.rs"
 crate-type = ["staticlib", "rlib"]
 
 # Cargo can't do autodiscovery if Cargo.toml is not in the root.
 [[bin]]
 name = "test_layout"
-path = "@path@/src/bin/test_layout.rs"
+path = "src/bin/test_layout.rs"
 
 [[example]]
 name = "test_layout"
-path = "@path@/examples/test_layout.rs"
+path = "examples/test_layout.rs"
 
 [[example]]
 name = "find_orphan_layouts"
-path = "@path@/examples/find_orphan_layouts.rs"
+path = "examples/find_orphan_layouts.rs"
 
 [features]
 zbus_v1_5 = []

meson.build

@@ -85,10 +85,16 @@ summary = [
 ]
 message('\n'.join(summary))
 
+# 'rust-analyzer' does not work correctly, when the paths in 'Cargo.toml' have '@path@' in them.
+cp = find_program('cp')
+sed = find_program('sed')
+copy_cargo_toml = run_command('cp', 'Cargo.toml', 'meson_Cargo.toml.in')
+prepare_cargo_toml = run_command('sed', '-i', 's/path = "/path = "@path@\//', 'meson_Cargo.toml.in')
+
 path_data = configuration_data()
 path_data.set('path', meson.source_root())
 cargo_toml = configure_file(
-    input: 'Cargo.toml',
+    input: 'meson_Cargo.toml.in',
     output: 'Cargo.toml',
     configuration: path_data,
 )