Improve completion of cfg attributes

The completion of cfg will look at the enabled cfg keys when
performing completion.

It will also look crate features when completing a feature cfg
option. A fixed list of known values for some cfg options are
provided.

For unknown keys it will look at the enabled values for that cfg key,
which means that completion will only show enabled options for those.

crates/base_db/src/fixture.rs

@@ -131,6 +131,7 @@ impl ChangeFixture {
                     meta.cfg,
                     meta.env,
                     Default::default(),
+                    Default::default(),
                 );
                 let prev = crates.insert(crate_name.clone(), crate_id);
                 assert!(prev.is_none());
@@ -160,6 +161,7 @@ impl ChangeFixture {
                 default_cfg,
                 Env::default(),
                 Default::default(),
+                Default::default(),
             );
         } else {
             for (from, to) in crate_deps {

crates/base_db/src/input.rs

@@ -192,6 +192,7 @@ pub struct CrateData {
     pub env: Env,
     pub dependencies: Vec<Dependency>,
     pub proc_macro: Vec<ProcMacro>,
+    pub features: FxHashMap<String, Vec<String>>,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -221,6 +222,7 @@ impl CrateGraph {
         cfg_options: CfgOptions,
         env: Env,
         proc_macro: Vec<ProcMacro>,
+        features: FxHashMap<String, Vec<String>>,
     ) -> CrateId {
         let data = CrateData {
             root_file_id: file_id,
@@ -230,6 +232,7 @@ impl CrateGraph {
             env,
             proc_macro,
             dependencies: Vec::new(),
+            features,
         };
         let crate_id = CrateId(self.arena.len() as u32);
         let prev = self.arena.insert(crate_id, data);
@@ -506,6 +509,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate2 = graph.add_crate_root(
             FileId(2u32),
@@ -514,6 +518,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate3 = graph.add_crate_root(
             FileId(3u32),
@@ -522,6 +527,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
         assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
@@ -538,6 +544,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate2 = graph.add_crate_root(
             FileId(2u32),
@@ -546,6 +553,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
         assert!(graph.add_dep(crate2, CrateName::new("crate2").unwrap(), crate2).is_err());
@@ -561,6 +569,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate2 = graph.add_crate_root(
             FileId(2u32),
@@ -569,6 +578,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate3 = graph.add_crate_root(
             FileId(3u32),
@@ -577,6 +587,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
         assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
@@ -592,6 +603,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         let crate2 = graph.add_crate_root(
             FileId(2u32),
@@ -600,6 +612,7 @@ mod tests {
             CfgOptions::default(),
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         assert!(graph
             .add_dep(crate1, CrateName::normalize_dashes("crate-name-with-dashes"), crate2)

crates/cfg/src/lib.rs

@@ -50,6 +50,26 @@ impl CfgOptions {
             self.enabled.remove(&atom);
         }
     }
+
+    pub fn get_cfg_keys(&self) -> Vec<&SmolStr> {
+        self.enabled
+            .iter()
+            .map(|x| match x {
+                CfgAtom::Flag(key) => key,
+                CfgAtom::KeyValue { key, .. } => key,
+            })
+            .collect()
+    }
+
+    pub fn get_cfg_values(&self, cfg_key: &str) -> Vec<&SmolStr> {
+        self.enabled
+            .iter()
+            .filter_map(|x| match x {
+                CfgAtom::KeyValue { key, value } if cfg_key == key => Some(value),
+                _ => None,
+            })
+            .collect()
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]

crates/hir/src/lib.rs

@@ -233,6 +233,10 @@ impl Crate {
     pub fn cfg(&self, db: &dyn HirDatabase) -> CfgOptions {
         db.crate_graph()[self.id].cfg_options.clone()
     }
+
+    pub fn features(&self, db: &dyn HirDatabase) -> Vec<String> {
+        db.crate_graph()[self.id].features.iter().map(|(feat, _)| feat.clone()).collect()
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]

crates/ide/src/lib.rs

@@ -220,6 +220,7 @@ impl Analysis {
             cfg_options,
             Env::default(),
             Default::default(),
+            Default::default(),
         );
         change.change_file(file_id, Some(Arc::new(text)));
         change.set_crate_graph(crate_graph);

crates/ide_completion/src/completions/attribute.rs

@@ -15,6 +15,7 @@ use crate::{
     Completions,
 };
 
+mod cfg;
 mod derive;
 mod lint;
 mod repr;
@@ -30,6 +31,9 @@ pub(crate) fn complete_attribute(acc: &mut Completions, ctx: &CompletionContext)
                 lint::complete_lint(acc, ctx, token_tree.clone(), DEFAULT_LINTS);
                 lint::complete_lint(acc, ctx, token_tree, CLIPPY_LINTS);
             }
+            "cfg" => {
+                cfg::complete_cfg(acc, ctx);
+            }
             _ => (),
         },
         (None, Some(_)) => (),
@@ -852,4 +856,15 @@ mod tests {
             "#]],
         );
     }
+
+    #[test]
+    fn test_cfg() {
+        check(
+            r#"#[cfg(target_endian = $0"#,
+            expect![[r#"
+                at little
+                at big
+"#]],
+        );
+    }
 }

crates/ide_completion/src/completions/attribute/cfg.rs

@@ -0,0 +1,126 @@
+//! Completion for cfg
+
+use std::iter;
+
+use syntax::SyntaxKind;
+
+use crate::{
+    completions::Completions, context::CompletionContext, item::CompletionKind, CompletionItem,
+    CompletionItemKind,
+};
+
+pub(crate) fn complete_cfg(acc: &mut Completions, ctx: &CompletionContext) {
+    let add_completion = |item: &&str| {
+        let mut completion =
+            CompletionItem::new(CompletionKind::Attribute, ctx.source_range(), *item);
+        completion.insert_text(format!(r#""{}""#, item));
+        completion.kind(CompletionItemKind::Attribute);
+        acc.add(completion.build());
+    };
+
+    let previous = iter::successors(ctx.original_token.prev_token(), |t| {
+        (matches!(t.kind(), SyntaxKind::EQ) || t.kind().is_trivia())
+            .then(|| t.prev_token())
+            .flatten()
+    })
+    .find(|t| matches!(t.kind(), SyntaxKind::IDENT));
+
+    match previous.as_ref().map(|p| p.text()) {
+        Some("feature") => {
+            ctx.krate.map(|krate| {
+                krate.features(ctx.db).iter().for_each(|f| {
+                    let mut item = CompletionItem::new(
+                        CompletionKind::Attribute,
+                        ctx.source_range(),
+                        f.clone(),
+                    );
+                    item.insert_text(format!(r#""{}""#, f));
+
+                    acc.add(item.build())
+                })
+            });
+        }
+        Some("target_arch") => KNOWN_ARCH.iter().for_each(add_completion),
+        Some("target_env") => KNOWN_ENV.iter().for_each(add_completion),
+        Some("target_os") => KNOWN_OS.iter().for_each(add_completion),
+        Some("target_vendor") => KNOWN_VENDOR.iter().for_each(add_completion),
+        Some("target_endian") => ["little", "big"].iter().for_each(add_completion),
+        Some(name) => {
+            ctx.krate.map(|krate| {
+                krate.cfg(ctx.db).get_cfg_values(&name).iter().for_each(|s| {
+                    let mut item = CompletionItem::new(
+                        CompletionKind::Attribute,
+                        ctx.source_range(),
+                        s.as_str(),
+                    );
+                    item.insert_text(format!(r#""{}""#, s));
+
+                    acc.add(item.build());
+                })
+            });
+        }
+        None => {
+            ctx.krate.map(|krate| {
+                krate.cfg(ctx.db).get_cfg_keys().iter().for_each(|s| {
+                    let item = CompletionItem::new(
+                        CompletionKind::Attribute,
+                        ctx.source_range(),
+                        s.as_str(),
+                    );
+                    acc.add(item.build());
+                })
+            });
+        }
+    };
+}
+
+const KNOWN_ARCH: [&'static str; 19] = [
+    "aarch64",
+    "arm",
+    "avr",
+    "hexagon",
+    "mips",
+    "mips64",
+    "msp430",
+    "nvptx64",
+    "powerpc",
+    "powerpc64",
+    "riscv32",
+    "riscv64",
+    "s390x",
+    "sparc",
+    "sparc64",
+    "wasm32",
+    "wasm64",
+    "x86",
+    "x86_64",
+];
+
+const KNOWN_ENV: [&'static str; 7] =
+    ["eabihf", "gnu", "gnueabihf", "msvc", "relibc", "sgx", "uclibc"];
+
+const KNOWN_OS: [&'static str; 20] = [
+    "cuda",
+    "dragonfly",
+    "emscripten",
+    "freebsd",
+    "fuchsia",
+    "haiku",
+    "hermit",
+    "illumos",
+    "l4re",
+    "linux",
+    "netbsd",
+    "none",
+    "openbsd",
+    "psp",
+    "redox",
+    "solaris",
+    "uefi",
+    "unknown",
+    "vxworks",
+    "windows",
+];
+
+const KNOWN_VENDOR: [&'static str; 8] =
+    ["apple", "fortanix", "nvidia", "pc", "sony", "unknown", "wrs", "uwp"];

crates/project_model/src/workspace.rs

@@ -387,6 +387,7 @@ fn project_json_to_crate_graph(
                     cfg_options,
                     env,
                     proc_macro.unwrap_or_default(),
+                    Default::default(),
                 ),
             )
         })
@@ -582,6 +583,7 @@ fn detached_files_to_crate_graph(
             cfg_options.clone(),
             Env::default(),
             Vec::new(),
+            Default::default(),
         );
 
         for (name, krate) in public_deps.iter() {
@@ -726,6 +728,7 @@ fn add_target_crate_root(
         cfg_options,
         env,
         proc_macro,
+        pkg.features.clone(),
     );
 
     crate_id
@@ -755,6 +758,7 @@ fn sysroot_to_crate_graph(
                 cfg_options.clone(),
                 env,
                 proc_macro,
+                Default::default(),
             );
             Some((krate, crate_id))
         })