13 files changed, 285 insertions(+), 2 deletions(-)

M pkg/parser/parser.go
M pkg/parser/testdata/invalid_interface.snow
M pkg/parser/testdata/invalid_interface.snow.err
M pkg/parser/testdata/invalid_interface.snow.want
A pkg/semantic/testdata/check/fn_generic_interface.snow.err
A pkg/semantic/testdata/check/fn_generic_interface.snow.want
A pkg/semantic/testdata/fn_generic_interface.snow
A pkg/semantic/testdata/scopes/fn_generic_interface.snow.err
A pkg/semantic/testdata/scopes/fn_generic_interface.snow.want
A pkg/semantic/testdata/static/fn_generic_interface.snow.err
A pkg/semantic/testdata/static/fn_generic_interface.snow.want
A pkg/semantic/testdata/types/fn_generic_interface.snow.err
A pkg/semantic/testdata/types/fn_generic_interface.snow.want

@@ 807,6 807,9 @@ func (p *parser) parseInterfaceDecl() *ast.InterfaceDecl {
 		if fn.Ref.IsValid() {
 			p.error(fn.Pos(), "interface method cannot be marked as ref")
 		}
+		if fn.GenericParams != nil {
+			p.error(fn.Pos(), "interface method cannot have a generic clause (the interface itself can)")
+		}
 		if fn.Body != nil {
 			p.error(fn.Pos(), "interface method cannot have a body")
 		}

@@ 5,4 5,6 @@ interface I {
   fn bar() {
     foo()
   }
+
+  fn quz[$T](t: $T)
 }

@@ 1,2 1,3 @@
 testdata/invalid_interface.snow:2:3: interface method cannot have attributes
 testdata/invalid_interface.snow:5:3: interface method cannot have a body
+testdata/invalid_interface.snow:9:3: interface method cannot have a generic clause (the interface itself can)

@@ 1,5 1,5 @@
-file [1, #0] [0:80]
-  interface [2] [0:80]
+file [1, #0] [0:101]
+  interface [3] [0:101]
     ident [I] [10:11]
     fn [16:50]
       @ [2] [16:39]


@@ 19,3 19,12 @@ file [1, #0] [0:80]
         expr [69:74]
           call [0] [69:74]
             ident [foo] [69:72]
+    fn [82:99]
+      ident [quz] [85:88]
+      generic [88:92]
+        param [89:91]
+          ident [$T] [89:91]
+      sig [1->0] [92:99]
+        param [93:98]
+          ident [t] [93:94]
+          ident [$T] [96:98]

@@ 0,0 1,1 @@
+testdata/fn_generic_interface.snow:23:14: cannot assign type struct G[bool] to variable of type interface I[int]

@@ 0,0 1,82 @@
+file testdata/fn_generic_interface.snow [0, 1, 2, 1]
+  fn main [let: () -> void]
+    block [10]
+      var:= ifaceInt [var: interface I[int]]
+        generic inst [1] [type: interface I[int]]
+          ident I [type: interface I]
+          ident int [type: int]
+        implicit conv [value: interface I[int]]
+          call [0] [value: struct S]
+            ident S [type: struct S]
+      var= res [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident ifaceInt [var: interface I[int]]
+            ident foo [let: (int) -> int]
+          int [1] [const: int]
+      var: gInt [var: struct G[int]]
+        generic inst [1] [type: struct G[int]]
+          ident G [type: struct G]
+          ident int [type: int]
+      var= gres [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident gInt [var: struct G[int]]
+            ident foo [let: (int) -> int]
+          int [1] [const: int]
+      assign
+        ident ifaceInt [var: interface I[int]]
+        implicit conv [value: interface I[int]]
+          call [0] [value: struct G[int]]
+            generic inst [1] [type: struct G[int]]
+              ident G [type: struct G]
+              ident int [type: int]
+      assign
+        ident res [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident ifaceInt [var: interface I[int]]
+            ident foo [let: (int) -> int]
+          int [2] [const: int]
+      assign
+        ident ifaceInt [var: interface I[int]]
+        call [0] [value: struct G[bool]]
+          generic inst [1] [type: struct G[bool]]
+            ident G [type: struct G]
+            ident bool [type: bool]
+      var: ifaceString [var: interface I[string]]
+        generic inst [1] [type: interface I[string]]
+          ident I [type: interface I]
+          ident string [type: string]
+      assign
+        ident ifaceString [var: interface I[string]]
+        implicit conv [value: interface I[string]]
+          call [0] [value: struct G[string]]
+            generic inst [1] [type: struct G[string]]
+              ident G [type: struct G]
+              ident string [type: string]
+      expr
+        call [1] [value: string]
+          select [let: (string) -> string]
+            ident ifaceString [var: interface I[string]]
+            ident foo [let: (string) -> string]
+          string ["a"] [const: string]
+  struct S [0, 1, 0, 0] [type: struct S]
+    fn foo [let: (int) -> int]
+      let: i [let: int]
+        ident int [type: int]
+      ident int [type: int]
+      block [0]
+  struct G [0, 1, 0, 0, $1] [type: struct G]
+    generic type $T [type: $T]
+    fn foo [let: ($T) -> $T]
+      let: t [let: $T]
+        ident $T [type: $T]
+      ident $T [type: $T]
+      block [0]
+  interface I [1, $1] [type: interface I]
+    generic type $T [type: $T]
+    fn foo [let: ($T) -> $T]
+      let: t [let: $T]
+        ident $T [type: $T]
+      ident $T [type: $T]

@@ 0,0 1,29 @@
+interface I[$T] {
+  fn foo(t: $T) -> $T
+}
+
+struct S {
+  fn foo(i: int) -> int {}
+}
+
+struct G[$T] {
+  fn foo(t: $T) -> $T {}
+}
+
+fn main() {
+  var ifaceInt: I[int] = S()
+  var res = ifaceInt.foo(1)
+  var gInt: G[int]
+  var gres = gInt.foo(1)
+
+  ifaceInt = G[int]()
+  res = ifaceInt.foo(2)
+
+  # this should fail
+  ifaceInt = G[bool]()
+
+  # this should work
+  var ifaceString: I[string]
+  ifaceString = G[string]()
+  ifaceString.foo("a")
+}

@@ 0,0 1,61 @@
+1 *semantic.Unit {
+.  bool
+.  extern
+.  f32
+.  f64
+.  false
+.  float
+.  i16
+.  i32
+.  i64
+.  i8
+.  int
+.  string
+.  true
+.  u16
+.  u32
+.  u64
+.  u8
+.  uint
+.  void
+.  2 *semantic.Struct {
+.  .  import
+.  .  pkg
+.  .  symbol
+.  }
+.  3 *semantic.File {
+.  .  G
+.  .  I
+.  .  S
+.  .  main
+.  .  4 *semantic.Interface {
+.  .  .  $T
+.  .  .  foo
+.  .  .  5 *semantic.Fn {
+.  .  .  .  t
+.  .  .  }
+.  .  }
+.  .  6 *semantic.Struct {
+.  .  .  foo
+.  .  .  7 *semantic.Fn {
+.  .  .  .  i
+.  .  .  .  self
+.  .  .  }
+.  .  }
+.  .  8 *semantic.Struct {
+.  .  .  $T
+.  .  .  foo
+.  .  .  9 *semantic.Fn {
+.  .  .  .  self
+.  .  .  .  t
+.  .  .  }
+.  .  }
+.  .  10 *semantic.Fn {
+.  .  .  gInt
+.  .  .  gres
+.  .  .  ifaceInt
+.  .  .  ifaceString
+.  .  .  res
+.  .  }
+.  }
+}

@@ 0,0 1,1 @@
+testdata/fn_generic_interface.snow:23:14: cannot assign type struct G[bool] to variable of type interface I[int]

@@ 0,0 1,15 @@
+testdata/fn_generic_interface.snow:14:26: S
+testdata/fn_generic_interface.snow:15:13: ifaceInt
+testdata/fn_generic_interface.snow:15:22: foo
+testdata/fn_generic_interface.snow:17:14: gInt
+testdata/fn_generic_interface.snow:17:19: foo
+testdata/fn_generic_interface.snow:19:14: G
+testdata/fn_generic_interface.snow:19:16: int
+testdata/fn_generic_interface.snow:20:9: ifaceInt
+testdata/fn_generic_interface.snow:20:18: foo
+testdata/fn_generic_interface.snow:23:14: G
+testdata/fn_generic_interface.snow:23:16: bool
+testdata/fn_generic_interface.snow:27:17: G
+testdata/fn_generic_interface.snow:27:19: string
+testdata/fn_generic_interface.snow:28:3: ifaceString
+testdata/fn_generic_interface.snow:28:15: foo

@@ 0,0 1,79 @@
+file testdata/fn_generic_interface.snow [0, 1, 2, 1]
+  fn main [let: () -> void]
+    block [10]
+      var:= ifaceInt [var: interface I[int]]
+        generic inst [1] [type: interface I[int]]
+          ident I [type: interface I]
+          ident int [type: int]
+        call [0] [value: struct S]
+          ident S [type: struct S]
+      var= res [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident ifaceInt [var: interface I[int]]
+            ident foo [let: (int) -> int]
+          int [1] [const: int]
+      var: gInt [var: struct G[int]]
+        generic inst [1] [type: struct G[int]]
+          ident G [type: struct G]
+          ident int [type: int]
+      var= gres [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident gInt [var: struct G[int]]
+            ident foo [let: (int) -> int]
+          int [1] [const: int]
+      assign
+        ident ifaceInt [var: interface I[int]]
+        call [0] [value: struct G[int]]
+          generic inst [1] [type: struct G[int]]
+            ident G [type: struct G]
+            ident int [type: int]
+      assign
+        ident res [var: int]
+        call [1] [value: int]
+          select [let: (int) -> int]
+            ident ifaceInt [var: interface I[int]]
+            ident foo [let: (int) -> int]
+          int [2] [const: int]
+      assign
+        ident ifaceInt [var: interface I[int]]
+        call [0] [value: struct G[bool]]
+          generic inst [1] [type: struct G[bool]]
+            ident G [type: struct G]
+            ident bool [type: bool]
+      var: ifaceString [var: interface I[string]]
+        generic inst [1] [type: interface I[string]]
+          ident I [type: interface I]
+          ident string [type: string]
+      assign
+        ident ifaceString [var: interface I[string]]
+        call [0] [value: struct G[string]]
+          generic inst [1] [type: struct G[string]]
+            ident G [type: struct G]
+            ident string [type: string]
+      expr
+        call [1] [value: string]
+          select [let: (string) -> string]
+            ident ifaceString [var: interface I[string]]
+            ident foo [let: (string) -> string]
+          string ["a"] [const: string]
+  struct S [0, 1, 0, 0] [type: struct S]
+    fn foo [let: (int) -> int]
+      let: i [let: int]
+        ident int [type: int]
+      ident int [type: int]
+      block [0]
+  struct G [0, 1, 0, 0, $1] [type: struct G]
+    generic type $T [type: $T]
+    fn foo [let: ($T) -> $T]
+      let: t [let: $T]
+        ident $T [type: $T]
+      ident $T [type: $T]
+      block [0]
+  interface I [1, $1] [type: interface I]
+    generic type $T [type: $T]
+    fn foo [let: ($T) -> $T]
+      let: t [let: $T]
+        ident $T [type: $T]
+      ident $T [type: $T]