Move the SWAY_GIT_TAG from forc into forc-pkg (FuelLabs#2448)

Move the SWAY_GIT_TAG from `forc` into `forc-pkg`

Closes FuelLabs#2447.

See this comment for context:
FuelLabs#2440 (comment)

forc-pkg/src/manifest.rs

@@ -105,11 +105,11 @@ impl ManifestFile {
     /// fields were used.
     ///
     /// If `core` and `std` are unspecified, `std` will be added to the `dependencies` table
-    /// implicitly. In this case, the `sway_git_tag` is used to specify the pinned commit at which
-    /// we fetch `std`.
-    pub fn from_file(path: PathBuf, sway_git_tag: &str) -> Result<Self> {
+    /// implicitly. In this case, the git tag associated with the version of this crate is used to
+    /// specify the pinned commit at which we fetch `std`.
+    pub fn from_file(path: PathBuf) -> Result<Self> {
         let path = path.canonicalize()?;
-        let manifest = Manifest::from_file(&path, sway_git_tag)?;
+        let manifest = Manifest::from_file(&path)?;
         Ok(Self { manifest, path })
     }
 
@@ -118,11 +118,11 @@ impl ManifestFile {
     ///
     /// This is short for `Manifest::from_file`, but takes care of constructing the path to the
     /// file.
-    pub fn from_dir(manifest_dir: &Path, sway_git_tag: &str) -> Result<Self> {
+    pub fn from_dir(manifest_dir: &Path) -> Result<Self> {
         let dir = forc_util::find_manifest_dir(manifest_dir)
             .ok_or_else(|| manifest_file_missing(manifest_dir))?;
         let path = dir.join(constants::MANIFEST_FILE_NAME);
-        Self::from_file(path, sway_git_tag)
+        Self::from_file(path)
     }
 
     /// Validate the `Manifest`.
@@ -232,9 +232,9 @@ impl Manifest {
     /// fields were used.
     ///
     /// If `core` and `std` are unspecified, `std` will be added to the `dependencies` table
-    /// implicitly. In this case, the `sway_git_tag` is used to specify the pinned commit at which
-    /// we fetch `std`.
-    pub fn from_file(path: &Path, sway_git_tag: &str) -> Result<Self> {
+    /// implicitly. In this case, the git tag associated with the version of this crate is used to
+    /// specify the pinned commit at which we fetch `std`.
+    pub fn from_file(path: &Path) -> Result<Self> {
         let manifest_str = std::fs::read_to_string(path)
             .map_err(|e| anyhow!("failed to read manifest at {:?}: {}", path, e))?;
         let toml_de = &mut toml::de::Deserializer::new(&manifest_str);
@@ -243,7 +243,7 @@ impl Manifest {
             println_yellow_err(&warning);
         })
         .map_err(|e| anyhow!("failed to parse manifest: {}.", e))?;
-        manifest.implicitly_include_std_if_missing(sway_git_tag);
+        manifest.implicitly_include_std_if_missing();
         manifest.implicitly_include_default_build_profiles_if_missing();
         manifest.validate()?;
         Ok(manifest)
@@ -265,10 +265,10 @@ impl Manifest {
     ///
     /// This is short for `Manifest::from_file`, but takes care of constructing the path to the
     /// file.
-    pub fn from_dir(dir: &Path, sway_git_tag: &str) -> Result<Self> {
+    pub fn from_dir(dir: &Path) -> Result<Self> {
         let manifest_dir = find_manifest_dir(dir).ok_or_else(|| manifest_file_missing(dir))?;
         let file_path = manifest_dir.join(constants::MANIFEST_FILE_NAME);
-        Self::from_file(&file_path, sway_git_tag)
+        Self::from_file(&file_path)
     }
 
     /// Produce an iterator yielding all listed dependencies.
@@ -311,7 +311,7 @@ impl Manifest {
     ///
     /// Note: If only `core` is specified, we are unable to implicitly add `std` as we cannot
     /// guarantee that the user's `core` is compatible with the implicit `std`.
-    fn implicitly_include_std_if_missing(&mut self, sway_git_tag: &str) {
+    fn implicitly_include_std_if_missing(&mut self) {
         use crate::{CORE, STD};
         // Don't include `std` if:
         // - this *is* `core` or `std`.
@@ -329,7 +329,7 @@ impl Manifest {
         // Add a `[dependencies]` table if there isn't one.
         let deps = self.dependencies.get_or_insert_with(Default::default);
         // Add the missing dependency.
-        let std_dep = implicit_std_dep(sway_git_tag.to_string());
+        let std_dep = implicit_std_dep();
         deps.insert(STD.to_string(), std_dep);
     }
 
@@ -425,11 +425,19 @@ impl Default for BuildProfile {
 }
 
 /// The definition for the implicit `std` dependency.
-fn implicit_std_dep(sway_git_tag: String) -> Dependency {
+fn implicit_std_dep() -> Dependency {
+    // The `forc-pkg` crate version formatted with the `v` prefix. E.g. "v1.2.3".
+    //
+    // This git tag is used during `Manifest` construction to pin the version of the implicit `std`
+    // dependency to the `forc-pkg` version.
+    //
+    // This is important to ensure that the version of `sway-core` that is baked into `forc-pkg` is
+    // compatible with the version of the `std` lib.
+    const SWAY_GIT_TAG: &str = concat!("v", env!("CARGO_PKG_VERSION"));
     const SWAY_GIT_REPO_URL: &str = "https://github.com/fuellabs/sway";
     let det = DependencyDetails {
         git: Some(SWAY_GIT_REPO_URL.to_string()),
-        tag: Some(sway_git_tag),
+        tag: Some(SWAY_GIT_TAG.to_string()),
         ..Default::default()
     };
     Dependency::Detailed(det)