From f6eb44cd9e2a27d2004386c71fb6c72f79ba83b3 Mon Sep 17 00:00:00 2001
From: Marcus Klaas de Vries <mail@marcusklaas.nl>
Date: Sat, 26 Jan 2019 19:25:57 +0100
Subject: Use type information from the turbofish

---
 crates/ra_hir/src/ty.rs                            | 34 ++++++++++++++++++----
 .../ra_hir/src/ty/snapshots/tests__generic_fn.snap |  7 +++--
 .../snapshots/tests__infer_function_generics.snap  |  8 ++---
 crates/ra_hir/src/ty/tests.rs                      |  3 ++
 4 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 9332aca9a..00a71a42f 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -1157,6 +1157,32 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         let typable = typable?;
         let ty = self.db.type_for_def(typable);
         let ty = self.insert_type_vars(ty);
+
+        // try to get generic parameters from the path and add them to the
+        // function type substitutions
+        if let Ty::FnDef { ref def, .. } = ty {
+            let last_seg_bindings = path
+                .segments
+                .last()
+                .and_then(|segment| segment.args_and_bindings.as_ref());
+            if let Some(generic_args) = last_seg_bindings {
+                let generic_params = def.generic_params(self.db);
+                if generic_args.args.len() == generic_params.params.len() {
+                    let substs = Ty::substs_from_path(
+                        self.db,
+                        &self.module,
+                        self.impl_block.as_ref(),
+                        &generic_params,
+                        path,
+                        (*def).into(),
+                    );
+                    return Some(ty.apply_substs(substs));
+                } else {
+                    // ERROR: incorrect number of type params
+                }
+            }
+        }
+
         Some(ty)
     }
 
@@ -1387,9 +1413,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
                 let (param_tys, ret_ty) = match &callee_ty {
                     Ty::FnPtr(sig) => (sig.input.clone(), sig.output.clone()),
-                    Ty::FnDef {
-                        def, substs, sig, ..
-                    } => {
+                    Ty::FnDef { substs, sig, .. } => {
                         let ret_ty = sig.output.clone().subst(&substs);
                         let param_tys = sig
                             .input
@@ -1437,9 +1461,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             (Ty::Unknown, Vec::new(), sig.output.clone())
                         }
                     }
-                    Ty::FnDef {
-                        def, substs, sig, ..
-                    } => {
+                    Ty::FnDef { substs, sig, .. } => {
                         let ret_ty = sig.output.clone().subst(&substs);
 
                         if sig.input.len() > 0 {
diff --git a/crates/ra_hir/src/ty/snapshots/tests__generic_fn.snap b/crates/ra_hir/src/ty/snapshots/tests__generic_fn.snap
index 84fbe6e4c..85aeefa0c 100644
--- a/crates/ra_hir/src/ty/snapshots/tests__generic_fn.snap
+++ b/crates/ra_hir/src/ty/snapshots/tests__generic_fn.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-01-26T17:46:03.963745056+00:00"
+created: "2019-01-26T18:16:16.568375+00:00"
 creator: insta@0.5.2
 expression: "&result"
 source: crates/ra_hir/src/ty/tests.rs
@@ -10,7 +10,7 @@ source: crates/ra_hir/src/ty/tests.rs
 [44; 45) 'x': &[unknown]
 [56; 65) '{     x }': &[unknown]
 [62; 63) 'x': &[unknown]
-[77; 138) '{     ...(z); }': ()
+[77; 197) '{     ...(1); }': ()
 [87; 88) 'y': u32
 [91; 96) '10u32': u32
 [102; 104) 'id': fn id<u32>(T) -> T
@@ -20,4 +20,7 @@ source: crates/ra_hir/src/ty/tests.rs
 [127; 132) 'clone': fn clone<bool>(&T) -> T
 [127; 135) 'clone(z)': bool
 [133; 134) 'z': &bool
+[173; 191) 'id::<i...tring>': fn id<i32>(T) -> T
+[173; 194) 'id::<i...ng>(1)': i32
+[192; 193) '1': i32
 
diff --git a/crates/ra_hir/src/ty/snapshots/tests__infer_function_generics.snap b/crates/ra_hir/src/ty/snapshots/tests__infer_function_generics.snap
index 369705f84..8ff6e55a6 100644
--- a/crates/ra_hir/src/ty/snapshots/tests__infer_function_generics.snap
+++ b/crates/ra_hir/src/ty/snapshots/tests__infer_function_generics.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-01-26T17:46:03.856278205+00:00"
+created: "2019-01-26T18:16:16.530712344+00:00"
 creator: insta@0.5.2
 expression: "&result"
 source: crates/ra_hir/src/ty/tests.rs
@@ -11,9 +11,9 @@ source: crates/ra_hir/src/ty/tests.rs
 [44; 46) 'id': fn id<u32>(T) -> T
 [44; 52) 'id(1u32)': u32
 [47; 51) '1u32': u32
-[58; 68) 'id::<i128>': fn id<i32>(T) -> T
-[58; 71) 'id::<i128>(1)': i32
-[69; 70) '1': i32
+[58; 68) 'id::<i128>': fn id<i128>(T) -> T
+[58; 71) 'id::<i128>(1)': i128
+[69; 70) '1': i128
 [81; 82) 'x': u64
 [90; 92) 'id': fn id<u64>(T) -> T
 [90; 95) 'id(1)': u64
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 40913b164..fac566626 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -611,6 +611,9 @@ fn test() {
     let y = 10u32;
     id(y);
     let x: bool = clone(z);
+
+    // bad turbofish - ignore!
+    id::<i128, String>(1);
 }
 "#,
     );
-- 
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