Implement warnings for unused imports

changelog/dmd.warnings-for-unused-imports.dd

@@ -0,0 +1,11 @@
+Warnings for unused imports
+
+The D frontend now issues warnings for unused imports if the source is compiled with -w or -wi.
+
+```d
+import std.stdio; // source.d(1): Warning: Import `std.stdio` is unused
+
+void main() {}
+```
+
+Imports that are added by default by the compiler are not flagged (i.e. object)

compiler/src/build.d

@@ -1574,7 +1574,7 @@ auto sourceFiles()
             parse.d parsetimevisitor.d permissivevisitor.d postordervisitor.d pragmasem.d printast.d rootobject.d safe.d
             semantic2.d semantic3.d sideeffect.d statement.d statement_rewrite_walker.d
             statementsem.d staticassert.d staticcond.d stmtstate.d target.d templatesem.d templateparamsem.d traits.d
-            transitivevisitor.d typesem.d typinf.d utils.d visitor.d foreachvar.d
+            transitivevisitor.d typesem.d typinf.d utils.d unused_import.d visitor.d foreachvar.d
             cparse.d
         "),
         backendHeaders: fileArray(env["C"], "

compiler/src/dmd/cparse.d

@@ -133,6 +133,7 @@ final class CParser(AST) : Parser!AST
                      * Import their definitions
                      */
                     auto s = new AST.Import(Loc.initial, null, Id.importc_builtins, null, false);
+                    s.used = true;
                     wrap.push(s);
                 }
 

compiler/src/dmd/dimport.d

@@ -41,6 +41,8 @@ extern (C++) final class Import : Dsymbol
     // corresponding AliasDeclarations for alias=name pairs
     AliasDeclarations aliasdecls;
 
+    bool used;
+
     extern (D) this(const ref Loc loc, Identifier[] packages, Identifier id, Identifier aliasId, int isstatic)
     {
         Identifier selectIdent()

compiler/src/dmd/dsymbol.d

@@ -1106,9 +1106,10 @@ extern (C++) class ScopeDsymbol : Dsymbol
     Dsymbols* members;          // all Dsymbol's in this scope
     DsymbolTable symtab;        // members[] sorted into table
     uint endlinnum;             // the linnumber of the statement after the scope (0 if unknown)
-    /// symbols whose members have been imported, i.e. imported modules and template mixins
-    Dsymbols* importedScopes;
-    Visibility.Kind* visibilities; // array of Visibility.Kind, one for each import
+    /// Hashtable of imported scopes:
+    // K = imported scopes i.e. the AST node for the imported modules or template mixins
+    // V = the import AST node or null in case of template mixins
+    Dsymbol[Dsymbol] importedScopes;
 
 private:
 
@@ -1186,57 +1187,21 @@ public:
         return os;
     }
 
-    void importScope(Dsymbol s, Visibility visibility) nothrow
+    void importScope(Dsymbol s, Visibility visibility, Import imp = null) nothrow
     {
         //printf("%s.ScopeDsymbol::importScope(%s, %d)\n", toChars(), s.toChars(), visibility);
         // No circular or redundant import's
         if (s != this)
         {
-            if (!importedScopes)
-                importedScopes = new Dsymbols();
-            else
+            if (s in importedScopes)
             {
-                for (size_t i = 0; i < importedScopes.length; i++)
-                {
-                    Dsymbol ss = (*importedScopes)[i];
-                    if (ss == s) // if already imported
-                    {
-                        if (visibility.kind > visibilities[i])
-                            visibilities[i] = visibility.kind; // upgrade access
-                        return;
-                    }
-                }
+                if (imp && visibility.kind > imp.visibility.kind)
+                    importedScopes[s] = imp;
+                return;
             }
-            importedScopes.push(s);
-            visibilities = cast(Visibility.Kind*)mem.xrealloc(visibilities, importedScopes.length * (visibilities[0]).sizeof);
-            visibilities[importedScopes.length - 1] = visibility.kind;
-        }
-    }
-
-
-    /*****************************************
-     * Returns: the symbols whose members have been imported, i.e. imported modules
-     * and template mixins.
-     *
-     * See_Also: importScope
-     */
-    extern (D) final Dsymbols* getImportedScopes() nothrow @nogc @safe pure
-    {
-        return importedScopes;
-    }
 
-    /*****************************************
-     * Returns: the array of visibilities associated with each imported scope. The
-     * length of the array matches the imported scopes array.
-     *
-     * See_Also: getImportedScopes
-     */
-    extern (D) final Visibility.Kind[] getImportVisibilities() nothrow @nogc @safe pure
-    {
-        if (!importedScopes)
-            return null;
-
-        return (() @trusted => visibilities[0 .. importedScopes.length])();
+            importedScopes[s] = imp ? imp : s;
+        }
     }
 
     extern (D) final void addAccessiblePackage(Package p, Visibility visibility) nothrow
@@ -1247,16 +1212,18 @@ public:
         (*pary)[p.tag] = true;
     }
 
-    bool isPackageAccessible(Package p, Visibility visibility, SearchOptFlags flags = SearchOpt.all) nothrow
+    bool isPackageAccessible(Package p, Visibility visibility, SearchOptFlags flags = SearchOpt.all)
     {
         if (p.tag < accessiblePackages.length && accessiblePackages[p.tag] ||
             visibility.kind == Visibility.Kind.private_ && p.tag < privateAccessiblePackages.length && privateAccessiblePackages[p.tag])
             return true;
-        foreach (i, ss; importedScopes ? (*importedScopes)[] : null)
+        foreach (sym, importer; importedScopes)
         {
+            auto imp = importer.isImport();
+
             // only search visible scopes && imported modules should ignore private imports
-            if (visibility.kind <= visibilities[i] &&
-                ss.isScopeDsymbol.isPackageAccessible(p, visibility, SearchOpt.ignorePrivateImports))
+            if ((!imp || visibility.kind <= imp.visibility.kind) &&
+                sym.isScopeDsymbol.isPackageAccessible(p, visibility, SearchOpt.ignorePrivateImports))
                 return true;
         }
         return false;
@@ -1536,11 +1503,11 @@ extern (C++) final class ForwardingScopeDsymbol : ScopeDsymbol
         return forward.symtabLookup(s,id);
     }
 
-    override void importScope(Dsymbol s, Visibility visibility)
+    override void importScope(Dsymbol s, Visibility visibility, Import imp = null)
     {
         auto forward = parent.isScopeDsymbol();
         assert(forward);
-        forward.importScope(s, visibility);
+        forward.importScope(s, visibility, imp);
     }
 
     override const(char)* kind()const{ return "local scope"; }

compiler/src/dmd/dsymbol.h

@@ -334,8 +334,7 @@ class ScopeDsymbol : public Dsymbol
     Dsymbols *members;          // all Dsymbol's in this scope
     DsymbolTable *symtab;       // members[] sorted into table
     unsigned endlinnum;         // the linnumber of the statement after the scope (0 if unknown)
-    Dsymbols *importedScopes;   // imported Dsymbol's
-    Visibility::Kind *visibilities;   // array of `Visibility.Kind`, one for each import
+    void *importedScopes;       // hashtable of imported scopes
 
 private:
     BitArray accessiblePackages, privateAccessiblePackages;

compiler/src/dmd/dsymbolsem.d

@@ -1670,7 +1670,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
 
                 if (!imp.isstatic)
                 {
-                    scopesym.importScope(imp.mod, imp.visibility);
+                    scopesym.importScope(imp.mod, imp.visibility, imp);
                 }
 
 
@@ -1689,6 +1689,8 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
 
             sc = sc.push(imp.mod);
             sc.visibility = imp.visibility;
+            if (imp.aliasdecls.length)
+                imp.used = true;
             for (size_t i = 0; i < imp.aliasdecls.length; i++)
             {
                 AliasDeclaration ad = imp.aliasdecls[i];
@@ -6149,14 +6151,16 @@ private extern(C++) class SearchVisitor : Visitor
         //printf(" look in imports\n");
         Dsymbol s = null;
         OverloadSet a = null;
+        Import importedFrom = null;
         // Look in imported modules
-        for (size_t i = 0; i < sds.importedScopes.length; i++)
+        foreach(sym, importer; sds.importedScopes)
         {
+            auto imp = importer.isImport();
             // If private import, don't search it
-            if ((flags & SearchOpt.ignorePrivateImports) && sds.visibilities[i] == Visibility.Kind.private_)
+            if ((flags & SearchOpt.ignorePrivateImports) && (imp && imp.visibility.kind == Visibility.Kind.private_))
                 continue;
             SearchOptFlags sflags = flags & (SearchOpt.ignoreErrors | SearchOpt.ignoreAmbiguous); // remember these in recursive searches
-            Dsymbol ss = (*sds.importedScopes)[i];
+            Dsymbol ss = sym;
             //printf("\tscanning import '%s', visibilities = %d, isModule = %p, isImport = %p\n", ss.toChars(), visibilities[i], ss.isModule(), ss.isImport());
 
             if (ss.isModule())
@@ -6181,6 +6185,7 @@ private extern(C++) class SearchVisitor : Visitor
             if (!s)
             {
                 s = s2;
+                importedFrom = imp;
                 if (s && s.isOverloadSet())
                     a = sds.mergeOverloadSet(ident, a, s);
             }
@@ -6194,7 +6199,10 @@ private extern(C++) class SearchVisitor : Visitor
                      * the other.
                      */
                     if (s.isDeprecated() || s.visible() < s2.visible() && s2.visible().kind != Visibility.Kind.none)
+                    {
                         s = s2;
+                        importedFrom = imp;
+                    }
                 }
                 else
                 {
@@ -6225,6 +6233,8 @@ private extern(C++) class SearchVisitor : Visitor
                             }
                             if (!symbolIsVisible(sds, s))
                                 s = s2;
+
+                            importedFrom = imp;
                             continue;
                         }
 
@@ -6272,6 +6282,13 @@ private extern(C++) class SearchVisitor : Visitor
                     a = sds.mergeOverloadSet(ident, a, s);
                 s = a;
             }
+            if (importedFrom)
+            {
+                importedFrom.used = true;
+                //if (sc.module_ && sc.module_.isRoot)
+                    //printf("import %s is used\n", importedFrom.toChars());
+            }
+
             //printf("\tfound in imports %s.%s\n", toChars(), s.toChars());
             return setResult(s);
         }
@@ -6897,7 +6914,7 @@ extern(C++) class ImportAllVisitor : Visitor
         if (sc.explicitVisibility)
             imp.visibility = sc.visibility;
         if (!imp.isstatic && !imp.aliasId && !imp.names.length)
-            sc.scopesym.importScope(imp.mod, imp.visibility);
+            sc.scopesym.importScope(imp.mod, imp.visibility, imp);
         // Enable access to pkgs/mod as soon as posible, because compiler
         // can traverse them before the import gets semantic (Issue: 21501)
         if (!imp.aliasId && !imp.names.length)
@@ -6935,6 +6952,8 @@ extern(C++) class ImportAllVisitor : Visitor
              (*m.members)[0].isImport() is null))
         {
             auto im = new Import(Loc.initial, null, Id.object, null, 0);
+            // consider it used;
+            im.used = true;
             m.members.shift(im);
         }
         if (!m.symtab)