Use empty prelude for compiler tools specs (#15272)

Apply some tiny refactors to specs that rely on features from the stdlib prelude. These seem to be not particularly relevant for the test scenario because we're testing compiler features, not stdlib implementations.

These changes allow using the compiler with the empty prelude which results in significantly less compilation effort.

The spec runtime for these tests reduces from 3:06 minutes to 13.81 seconds (over 90% reduction! 🎉🚀)

spec/compiler/crystal/tools/context_spec.cr

@@ -3,6 +3,7 @@ require "../../../spec_helper"
 private def processed_context_visitor(code, cursor_location)
   compiler = Compiler.new
   compiler.no_codegen = true
+  compiler.prelude = "empty"
   result = compiler.compile(Compiler::Source.new(".", code), "fake-no-build")
 
   visitor = ContextVisitor.new(cursor_location)
@@ -118,15 +119,20 @@ describe "context" do
   it "includes last call" do
     assert_context_includes %(
       class Foo
-        property lorem
+        def lorem
+          @lorem
+        end
 
         def initialize(@lorem : Int64)
         end
       end
 
+      def foo(f)
+      end
+
       f = Foo.new(1i64)
 
-      puts f.lo‸rem
+      foo f.lo‸rem
       1
     ), "f.lorem", ["Int64"]
   end
@@ -141,9 +147,13 @@ describe "context" do
 
   it "does includes regex special variables" do
     assert_context_keys %(
+      def match
+        $~ = "match"
+      end
+
       def foo
-        s = "string"
-        s =~ /s/
+        s = "foo"
+        match
         ‸
         0
       end
@@ -185,23 +195,15 @@ describe "context" do
 
   it "can handle union types" do
     assert_context_includes %(
-    a = if rand() > 0
-      1i64
-    else
-      "foo"
-    end
+    a = 1_i64.as(Int64 | String)
     ‸
     0
     ), "a", ["(Int64 | String)"]
   end
 
   it "can display text output" do
     run_context_tool(%(
-    a = if rand() > 0
-      1i64
-    else
-      "foo"
-    end
+    a = 1_i64.as(Int64 | String)
     ‸
     0
     )) do |result|
@@ -218,11 +220,7 @@ describe "context" do
 
   it "can display json output" do
     run_context_tool(%(
-    a = if rand() > 0
-      1i64
-    else
-      "foo"
-    end
+    a = 1_i64.as(Int64 | String)
     ‸
     0
     )) do |result|

spec/compiler/crystal/tools/expand_spec.cr

@@ -5,6 +5,7 @@ private def processed_expand_visitor(code, cursor_location)
   compiler.no_codegen = true
   compiler.no_cleanup = true
   compiler.wants_doc = true
+  compiler.prelude = "empty"
   result = compiler.compile(Compiler::Source.new(".", code), "fake-no-build")
 
   visitor = ExpandVisitor.new(cursor_location)

spec/compiler/crystal/tools/implementations_spec.cr

@@ -3,6 +3,7 @@ require "../../../spec_helper"
 private def processed_implementation_visitor(code, cursor_location)
   compiler = Compiler.new
   compiler.no_codegen = true
+  compiler.prelude = "empty"
   result = compiler.compile(Compiler::Source.new(".", code), "fake-no-build")
 
   visitor = ImplementationsVisitor.new(cursor_location)
@@ -52,7 +53,7 @@ describe "implementations" do
         1
       end
 
-      puts f‸oo
+      f‸oo
     )
   end
 
@@ -117,7 +118,6 @@ describe "implementations" do
       end
 
       while f‸oo
-        puts 2
       end
     )
   end
@@ -129,7 +129,6 @@ describe "implementations" do
       end
 
       if f‸oo
-        puts 2
       end
     )
   end
@@ -140,7 +139,7 @@ describe "implementations" do
         1
       end
 
-      puts 2 if f‸oo
+      2 if f‸oo
     )
   end
 
@@ -151,7 +150,6 @@ describe "implementations" do
       end
 
       begin
-        puts 2
       rescue
         f‸oo
       end