[backport] fix #12528, fix #12525: incorrect generic type resolution for default values (#12538)

compiler/sigmatch.nim

@@ -134,11 +134,14 @@ proc initCandidate*(ctx: PContext, c: var TCandidate, callee: PType) =
   initIdTable(c.bindings)
 
 proc put(c: var TCandidate, key, val: PType) {.inline.} =
+  ## Given: proc foo[T](x: T); foo(4)
+  ## key: 'T'
+  ## val: 'int' (typeof(4))
   when false:
     let old = PType(idTableGet(c.bindings, key))
     if old != nil:
       echo "Putting ", typeToString(key), " ", typeToString(val), " and old is ", typeToString(old)
-      if typeToString(old) == "seq[string]":
+      if typeToString(old) == "float32":
         writeStackTrace()
     if c.c.module.name.s == "temp3":
       echo "binding ", key, " -> ", val
@@ -2551,13 +2554,18 @@ proc matches*(c: PContext, n, nOrig: PNode, m: var TCandidate) =
                       formal.name.s)
         if nfDefaultRefsParam in formal.ast.flags:
           m.call.flags.incl nfDefaultRefsParam
-        var def = copyTree(formal.ast)
-        if def.kind == nkNilLit:
-          def = implicitConv(nkHiddenStdConv, formal.typ, def, m, c)
+        var defaultValue = copyTree(formal.ast)
+        if defaultValue.kind == nkNilLit:
+          defaultValue = implicitConv(nkHiddenStdConv, formal.typ, defaultValue, m, c)
+        # proc foo(x: T = 0.0)
+        # foo()
         if {tfImplicitTypeParam, tfGenericTypeParam} * formal.typ.flags != {}:
-          put(m, formal.typ, def.typ)
-        def.flags.incl nfDefaultParam
-        setSon(m.call, formal.position + 1, def)
+          let existing = PType(idTableGet(m.bindings, formal.typ))
+          if existing == nil or existing.kind == tyTypeDesc:
+            # see bug #11600:
+            put(m, formal.typ, defaultValue.typ)
+        defaultValue.flags.incl nfDefaultParam
+        setSon(m.call, formal.position + 1, defaultValue)
     inc(f)
   # forget all inferred types if the overload matching failed
   if m.state == csNoMatch:

lib/pure/complex.nim

@@ -451,3 +451,6 @@ when isMainModule:
   doAssert(sizeof(a) == 16)
 
   doAssert 123.0.im + 456.0 == complex64(456, 123)
+
+  var localA = complex(0.1'f32)
+  doAssert localA.im is float32

tests/generics/tgeneric0.nim

@@ -2,6 +2,8 @@ discard """
   output: '''
 100
 0
+float32
+float32
 '''
 """
 
@@ -110,3 +112,15 @@ block tgeneric4:
       newSeq result.free, 0
 
   var x = newIDGen[int]()
+
+block tgeneric5:
+  # bug #12528
+  proc foo[T](a: T; b: T) =
+    echo T
+
+  foo(0.0'f32, 0.0)
+
+  proc bar[T](a: T; b: T = 0.0) =
+    echo T
+
+  bar(0.0'f32)