feat(complete): Added completion for --profile (#15308)

### What does this PR try to resolve?

This attempts to complete the autocompleter for `cargo build --profile
<TAB>`, it loads the built in profiles and the custom profile present in
`Cargo.toml` and `.cargo/config.toml` if present when pressing TAB key,
in the completion value it also adds an description inspired by
[this](https://github.com/rust-lang/cargo/blob/master/src/cargo/core/compiler/job_queue/mod.rs#L805-L813)

![Screenshot from 2025-03-14
02-17-40](https://github.com/user-attachments/assets/6fc784a0-e3e7-4deb-9252-847d720894c1)

Related to #14520

Author: epage

src/cargo/core/profiles.rs

@@ -391,6 +391,11 @@ impl Profiles {
             .get(name)
             .ok_or_else(|| anyhow::format_err!("profile `{}` is not defined", name))
     }
+
+    /// Returns an iterator over all profile names known to Cargo.
+    pub fn profile_names(&self) -> impl Iterator<Item = InternedString> + '_ {
+        self.by_name.keys().copied()
+    }
 }
 
 /// An object used for handling the profile hierarchy.

src/cargo/util/command_prelude.rs

@@ -2,7 +2,7 @@ use crate::core::compiler::{
     BuildConfig, CompileKind, MessageFormat, RustcTargetData, TimingOutput,
 };
 use crate::core::resolver::{CliFeatures, ForceAllTargets, HasDevUnits};
-use crate::core::{shell, Edition, Package, Target, TargetKind, Workspace};
+use crate::core::{profiles::Profiles, shell, Edition, Package, Target, TargetKind, Workspace};
 use crate::ops::lockfile::LOCKFILE_NAME;
 use crate::ops::registry::RegistryOrIndex;
 use crate::ops::{self, CompileFilter, CompileOptions, NewOptions, Packages, VersionControl};
@@ -274,7 +274,11 @@ pub trait CommandExt: Sized {
         self._arg(
             opt("profile", profile)
                 .value_name("PROFILE-NAME")
-                .help_heading(heading::COMPILATION_OPTIONS),
+                .help_heading(heading::COMPILATION_OPTIONS)
+                .add(clap_complete::ArgValueCandidates::new(|| {
+                    let candidates = get_profile_candidates();
+                    candidates
+                })),
         )
     }
 
@@ -1118,6 +1122,53 @@ pub fn get_registry_candidates() -> CargoResult<Vec<clap_complete::CompletionCan
     }
 }
 
+fn get_profile_candidates() -> Vec<clap_complete::CompletionCandidate> {
+    match get_workspace_profile_candidates() {
+        Ok(candidates) if !candidates.is_empty() => candidates,
+        // fallback to default profile candidates
+        _ => default_profile_candidates(),
+    }
+}
+
+fn get_workspace_profile_candidates() -> CargoResult<Vec<clap_complete::CompletionCandidate>> {
+    let gctx = new_gctx_for_completions()?;
+    let ws = Workspace::new(&find_root_manifest_for_wd(gctx.cwd())?, &gctx)?;
+    let profiles = Profiles::new(&ws, InternedString::new("dev"))?;
+
+    let mut candidates = Vec::new();
+    for name in profiles.profile_names() {
+        let Ok(profile_instance) = Profiles::new(&ws, name) else {
+            continue;
+        };
+        let base_profile = profile_instance.base_profile();
+
+        let mut description = String::from(if base_profile.opt_level.as_str() == "0" {
+            "unoptimized"
+        } else {
+            "optimized"
+        });
+
+        if base_profile.debuginfo.is_turned_on() {
+            description.push_str(" + debuginfo");
+        }
+
+        candidates
+            .push(clap_complete::CompletionCandidate::new(&name).help(Some(description.into())));
+    }
+
+    Ok(candidates)
+}
+
+fn default_profile_candidates() -> Vec<clap_complete::CompletionCandidate> {
+    vec![
+        clap_complete::CompletionCandidate::new("dev").help(Some("unoptimized + debuginfo".into())),
+        clap_complete::CompletionCandidate::new("release").help(Some("optimized".into())),
+        clap_complete::CompletionCandidate::new("test")
+            .help(Some("unoptimized + debuginfo".into())),
+        clap_complete::CompletionCandidate::new("bench").help(Some("optimized".into())),
+    ]
+}
+
 fn get_example_candidates() -> Vec<clap_complete::CompletionCandidate> {
     get_targets_from_metadata()
         .unwrap_or_default()