tools: Shuffle go code into an idiomatic tree

main packages usually go under a `cmd` directory.
Hoist utility packages to the root `src` directroy so they can be shared.

Change-Id: I0c221f6cd39980f5c202c030cd5134d775533efa
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50901
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

tools/src/substr/substr.go

@@ -0,0 +1,52 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package substr
+
+import (
+	diff "github.com/sergi/go-diff/diffmatchpatch"
+)
+
+// Fix attempts to reconstruct substr by comparing it to body.
+// substr is a fuzzy substring of body.
+// Fix returns a new exact substring of body, by calculating a diff of the text.
+// If no match could be made, Fix() returns an empty string.
+func Fix(body, substr string) string {
+	dmp := diff.New()
+
+	diffs := dmp.DiffMain(body, substr, false)
+	if len(diffs) == 0 {
+		return ""
+	}
+
+	front := func() diff.Diff { return diffs[0] }
+	back := func() diff.Diff { return diffs[len(diffs)-1] }
+
+	start, end := 0, len(body)
+
+	// Trim edits that remove text from body start
+	for len(diffs) > 0 && front().Type == diff.DiffDelete {
+		start += len(front().Text)
+		diffs = diffs[1:]
+	}
+
+	// Trim edits that remove text from body end
+	for len(diffs) > 0 && back().Type == diff.DiffDelete {
+		end -= len(back().Text)
+		diffs = diffs[:len(diffs)-1]
+	}
+
+	// New substring is the span for the remainder of the edits
+	return body[start:end]
+}

tools/src/substr/substr_test.go

@@ -0,0 +1,275 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package substr
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestFixSubstr(t *testing.T) {
+	type test struct {
+		body   string
+		substr string
+		expect string
+	}
+
+	for _, test := range []test{
+		{
+			body:   "abc_def_ghi_jkl_mno",
+			substr: "def_XXX_jkl",
+			expect: "def_ghi_jkl",
+		},
+		{
+			body:   "abc\ndef\nghi\njkl\nmno",
+			substr: "def\nXXX\njkl",
+			expect: "def\nghi\njkl",
+		},
+		{
+			body:   "aaaaa12345ccccc",
+			substr: "1x345",
+			expect: "12345",
+		},
+		{
+			body:   "aaaaa12345ccccc",
+			substr: "12x45",
+			expect: "12345",
+		},
+		{
+			body:   "aaaaa12345ccccc",
+			substr: "123x5",
+			expect: "12345",
+		},
+		{
+			body:   "aaaaaaaaaaaaa",
+			substr: "bbbbbbbbbbbbb",
+			expect: "", // cannot produce a sensible diff
+		}, { ///////////////////////////////////////////////////////////////////
+			body: `Return{
+  {
+    ScalarConstructor[not set]{42u}
+  }
+}
+`,
+			substr: `Return{
+  {
+    ScalarConstructor[not set]{42}
+  }
+}`,
+			expect: `Return{
+  {
+    ScalarConstructor[not set]{42u}
+  }
+}`,
+		}, { ///////////////////////////////////////////////////////////////////
+			body: `VariableDeclStatement{
+  Variable{
+    x_1
+    function
+    __u32
+  }
+}
+Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{42u}
+}
+Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{0u}
+}
+Return{}
+`,
+			substr: `Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{42}
+}
+Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{0}
+}`,
+			expect: `Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{42u}
+}
+Assignment{
+  Identifier[not set]{x_1}
+  ScalarConstructor[not set]{0u}
+}`,
+		}, { ///////////////////////////////////////////////////////////////////
+			body: `VariableDeclStatement{
+  Variable{
+    a
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{true}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    b
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{false}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    c
+    function
+    __i32
+    {
+      ScalarConstructor[not set]{-1}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    d
+    function
+    __u32
+    {
+      ScalarConstructor[not set]{1u}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    e
+    function
+    __f32
+    {
+      ScalarConstructor[not set]{1.500000}
+    }
+  }
+}
+`,
+			substr: `VariableDeclStatement{
+  Variable{
+    a
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{true}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    b
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{false}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    c
+    function
+    __i32
+    {
+      ScalarConstructor[not set]{-1}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    d
+    function
+    __u32
+    {
+      ScalarConstructor[not set]{1}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    e
+    function
+    __f32
+    {
+      ScalarConstructor[not set]{1.500000}
+    }
+  }
+}
+`,
+			expect: `VariableDeclStatement{
+  Variable{
+    a
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{true}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    b
+    function
+    __bool
+    {
+      ScalarConstructor[not set]{false}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    c
+    function
+    __i32
+    {
+      ScalarConstructor[not set]{-1}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    d
+    function
+    __u32
+    {
+      ScalarConstructor[not set]{1u}
+    }
+  }
+}
+VariableDeclStatement{
+  Variable{
+    e
+    function
+    __f32
+    {
+      ScalarConstructor[not set]{1.500000}
+    }
+  }
+}
+`,
+		},
+	} {
+		body := strings.ReplaceAll(test.body, "\n", "␤")
+		substr := strings.ReplaceAll(test.substr, "\n", "␤")
+		expect := strings.ReplaceAll(test.expect, "\n", `␤`)
+		got := strings.ReplaceAll(Fix(test.body, test.substr), "\n", "␤")
+		if got != expect {
+			t.Errorf("Test failure:\nbody:   '%v'\nsubstr: '%v'\nexpect: '%v'\ngot:    '%v'\n\n", body, substr, expect, got)
+		}
+
+	}
+}